Merge dev/mesh-tool: mesht v1

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MmdG9GqfSWCzts7AkDwRDh

.gitea/workflows/release.yml

@@ -0,0 +1,105 @@
+name: release-tools
+
+# På varje push till master/main: bygg de tools som fått ändringar
+# (linux x64 + arm64) och lägg binärerna på en rullande
+# "<tool>-latest"-release på släppsidan i Gitea.
+on:
+  push:
+    branches: [master, main]
+  workflow_dispatch: {} # manuell körning bygger ALLA tools
+
+jobs:
+  build-release:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0 # hela historiken behövs för diffen mot 'before'
+
+      - name: Detektera ändrade tools
+        id: changed
+        run: |
+          TOOLS="pixel-sprite-maker mesh-tool"
+          BEFORE="${{ github.event.before }}"
+          CHANGED=""
+          if [ "${{ github.event_name }}" = "workflow_dispatch" ] \
+             || [ -z "$BEFORE" ] \
+             || echo "$BEFORE" | grep -Eq '^0+$' \
+             || ! git cat-file -e "$BEFORE" 2>/dev/null; then
+            echo "första push / manuell körning -> bygger alla tools"
+            CHANGED="$TOOLS"
+          else
+            for t in $TOOLS; do
+              if ! git diff --quiet "$BEFORE" "${{ github.sha }}" -- "$t/"; then
+                CHANGED="$CHANGED $t"
+              fi
+            done
+          fi
+          CHANGED="$(echo $CHANGED)"   # trimma whitespace
+          echo "tools=$CHANGED" >> "$GITHUB_OUTPUT"
+          echo "bygger: ${CHANGED:-inget}"
+
+      - name: Installera Go
+        if: steps.changed.outputs.tools != ''
+        uses: actions/setup-go@v5
+        with:
+          go-version: "1.24"
+          cache: false
+
+      - name: Testa + bygg (x64 + arm64)
+        if: steps.changed.outputs.tools != ''
+        run: |
+          set -e
+          VERSION="latest-$(git rev-parse --short HEAD)"
+          for t in ${{ steps.changed.outputs.tools }}; do
+            case "$t" in
+              pixel-sprite-maker) BIN=spritec ;;
+              mesh-tool)          BIN=mesht ;;
+              *) echo "okänt tool $t"; exit 1 ;;
+            esac
+            echo "=== $t ($BIN) ==="
+            cd "$t"
+            go test ./...
+            mkdir -p build
+            GOOS=linux GOARCH=amd64 go build -trimpath \
+              -ldflags "-s -w -X main.version=$VERSION" -o "build/$BIN-linux-x64" .
+            GOOS=linux GOARCH=arm64 go build -trimpath \
+              -ldflags "-s -w -X main.version=$VERSION" -o "build/$BIN-linux-arm64" .
+            (cd build && sha256sum "$BIN"-linux-* > checksums.txt && ls -la)
+            cd ..
+          done
+
+      - name: Skapa/uppdatera releaser + ladda upp binärer
+        if: steps.changed.outputs.tools != ''
+        env:
+          API: http://gitea-d:3000/api/v1
+          REPO: ${{ github.repository }}
+          TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          set -e
+          for t in ${{ steps.changed.outputs.tools }}; do
+            case "$t" in
+              pixel-sprite-maker) BIN=spritec ;;
+              mesh-tool)          BIN=mesht ;;
+            esac
+            TAG="$t-latest"
+            BODY="$t (binär: $BIN) - rullande bygge från senaste master. Commit: ${{ github.sha }}. Arkitekturer: linux x64 + arm64 (Pi5)."
+            rid=$(curl -s -X POST "$API/repos/$REPO/releases" \
+              -H "Authorization: token $TOKEN" -H 'Content-Type: application/json' \
+              -d "{\"tag_name\":\"$TAG\",\"name\":\"$TAG\",\"body\":\"$BODY\"}" | jq -r '.id // empty')
+            [ -z "$rid" ] && rid=$(curl -s "$API/repos/$REPO/releases/tags/$TAG" \
+              -H "Authorization: token $TOKEN" | jq -r '.id')
+            echo "$t -> release id $rid"
+            for f in "$BIN-linux-x64" "$BIN-linux-arm64" checksums.txt; do
+              aid=$(curl -s "$API/repos/$REPO/releases/$rid/assets" \
+                -H "Authorization: token $TOKEN" | jq -r ".[] | select(.name==\"$f\") | .id")
+              if [ -n "$aid" ] && [ "$aid" != "null" ]; then
+                curl -s -X DELETE "$API/repos/$REPO/releases/$rid/assets/$aid" \
+                  -H "Authorization: token $TOKEN" -o /dev/null
+              fi
+              curl -s -X POST "$API/repos/$REPO/releases/$rid/assets?name=$f" \
+                -H "Authorization: token $TOKEN" \
+                -F "attachment=@$t/build/$f" -o /dev/null -w "  $f -> HTTP %{http_code}\n"
+            done
+          done

.gitignore

@@ -0,0 +1,3 @@
+build/
+*.exe
+mesh-tool/examples/downloads/

.vscode/tasks.json

@@ -0,0 +1,44 @@
+{
+  "version": "2.0.0",
+  "tasks": [
+    {
+      "label": "build pixel-sprite-maker",
+      "type": "shell",
+      "command": "go build -trimpath -ldflags '-s -w' -o build/spritec .",
+      "options": { "cwd": "${workspaceFolder}/pixel-sprite-maker" },
+      "group": "build",
+      "problemMatcher": ["$go"]
+    },
+    {
+      "label": "build mesh-tool",
+      "type": "shell",
+      "command": "go build -trimpath -ldflags '-s -w' -o build/mesht .",
+      "options": { "cwd": "${workspaceFolder}/mesh-tool" },
+      "group": "build",
+      "problemMatcher": ["$go"]
+    },
+    {
+      "label": "test pixel-sprite-maker",
+      "type": "shell",
+      "command": "go test ./...",
+      "options": { "cwd": "${workspaceFolder}/pixel-sprite-maker" },
+      "group": "test",
+      "problemMatcher": ["$go"]
+    },
+    {
+      "label": "test mesh-tool",
+      "type": "shell",
+      "command": "go test ./...",
+      "options": { "cwd": "${workspaceFolder}/mesh-tool" },
+      "group": "test",
+      "problemMatcher": ["$go"]
+    },
+    {
+      "label": "build",
+      "dependsOn": ["build pixel-sprite-maker", "build mesh-tool"],
+      "dependsOrder": "parallel",
+      "group": { "kind": "build", "isDefault": true },
+      "problemMatcher": []
+    }
+  ]
+}

README.md

@@ -1,3 +1,46 @@
 # agent-tools
 
-smal tools for ai agents
+Small, self-contained CLI tools built for **AI agents** to use during
+development work. Every tool is a single static Go binary with a
+text-first interface: input formats an agent can read and write
+directly, and output (names, errors, previews) explicit enough that the
+agent understands the result without opening an image viewer.
+
+| Tool | Binary | What it does |
+|------|--------|--------------|
+| [`pixel-sprite-maker/`](pixel-sprite-maker/) | `spritec` | Turns `.sprite` text files (palette + character grid) into PNG/JPG/SVG pixel art, up to 256x256 px per sprite. Combines several sprites into sprite sheets / animation strips whose **file names document the layout** (`walk_8x8_4x1.png` = 8x8 px frames, 4 columns, 1 row). |
+| [`mesh-tool/`](mesh-tool/) | `mesht` | Creates, inspects and edits 3D models (OBJ + STL). ASCII multi-view rendering + measurements (bbox, volume, watertightness) let an agent *see* a model, edit it (scale/rotate/mirror/merge/primitives) and verify the result. |
+
+Each tool has its own folder, its own README with the full format/CLI
+reference, its own tests and its own dev branch (`dev/<tool>`).
+
+## Building
+
+```bash
+# Arch/Garuda prerequisite:
+sudo pacman -S go
+
+cd <tool>/ && go build -o build/<binary> .    # per tool
+go test ./...                                 # per tool
+```
+
+VS Code: **Terminal → Run Build Task** — `build` builds every tool into
+its own `<tool>/build/` folder; per-tool `build <tool>` and
+`test <tool>` tasks also exist.
+
+## CI / releases
+
+`.gitea/workflows/release.yml` runs on every push to `master`/`main` on
+the self-hosted runner: tools whose folders changed are tested, built
+for **linux x64 + arm64** (the Pi5), and published to a rolling
+release per tool on the repo's release page:
+
+- tag `pixel-sprite-maker-latest` → assets `spritec-linux-x64`, `spritec-linux-arm64`, `checksums.txt`
+- tag `mesh-tool-latest` → assets `mesht-linux-x64`, `mesht-linux-arm64`, `checksums.txt`
+
+A manual `workflow_dispatch` run builds all tools regardless of diffs.
+
+## Branch layout
+
+- `main` — stable, releases are built from here
+- `dev/pixel-sprite-maker`, `dev/mesh-tool` — per-tool development branches

doc/plan.md

@@ -0,0 +1,43 @@
+# agent-tools — plan
+
+## Goal
+
+A collection of small, agent-friendly CLI tools. The common thread:
+**text in, verifiable artifacts out**. An agent should be able to author
+the input format directly, predict what the output will look like, and
+verify results without a GUI.
+
+## Stack
+
+- Go (single static binaries, zero deps, trivial cross-compile to the
+  Pi5's arm64 runner), one Go module per tool.
+- Targets: linux x64 + linux arm64.
+
+## Deploy target
+
+Pattern A (distributable binaries): rolling `<tool>-latest` release per
+tool on Gitea, built by `.gitea/workflows/release.yml` on push to
+master/main. Only tools whose folders changed get rebuilt.
+
+## Milestones
+
+1. ✅ `pixel-sprite-maker` (`spritec`): .sprite text format → PNG/JPG/SVG,
+   sprite sheets with self-documenting file names, terminal preview.
+2. ✅ `mesh-tool` (`mesht`): OBJ/STL create/inspect/edit with ASCII
+   multi-view rendering, measurements and watertightness checks.
+3. ✅ Per-tool VS Code build tasks → `<tool>/build/`.
+4. ✅ CI: changed-tool detection + per-tool rolling releases.
+
+## Roadmap / expansion ideas (not agreed yet)
+
+- spritec: palette import from image files, GIF export for animations,
+  tile-map composer (map file referencing sprite tiles).
+- mesht: OBJ vertex-color support, simple boolean ops (union via
+  voxelization), PNG snapshot rendering, glTF export.
+- New tools: bitmap-font maker, sound-effect generator (sfxr-style text
+  presets), tiled-map (.tmx) writer.
+
+## Open questions
+
+- Versioned releases (`vX.Y.Z` tags per tool) on top of the rolling
+  `latest` — add when something depends on a pinned version.

mesh-tool/.gitignore

@@ -0,0 +1,2 @@
+build/
+examples/downloads/

mesh-tool/README.md

@@ -0,0 +1,101 @@
+# mesh-tool (`mesht`)
+
+Create, inspect and edit **3D models** from the command line — built so an
+agent can *see* a model (ASCII multi-view rendering + measurements),
+reason about it, and edit it step by step. Written in Go, zero
+dependencies, single static binary.
+
+## Formats
+
+| Format | Read | Write | Notes |
+|--------|------|-------|-------|
+| OBJ    | ✔    | ✔     | multiple named objects, quads/ngons triangulated |
+| STL    | ✔    | ✔     | binary + ASCII, auto-detected; vertices re-welded on load |
+
+OBJ and STL cover the vast majority of simple editing/printing/game
+pipelines and are plain enough to survive round-trips. glTF/GLB is out of
+scope for now (a full JSON+buffer+material model; use Blender for that).
+
+Normals, UVs and materials are ignored on read — this tool edits
+*geometry*. Viewers recompute normals; STL export writes correct face
+normals from the winding.
+
+## Build
+
+```bash
+# Arch/Garuda: sudo pacman -S go
+cd mesh-tool
+go build -o build/mesht .        # or the VS Code task "build mesh-tool"
+go test ./...
+```
+
+## Commands
+
+```bash
+mesht info model.obj           # verts/tris, bbox, size, area, volume, watertight?
+mesht view model.obj           # ASCII render: front, side, top (default)
+mesht view model.obj --views iso --width 100 --object wheel
+
+# creation — box|sphere|cylinder|cone|plane|torus
+mesht create box --size 2,1,1 --name crate -o crate.obj
+mesht create sphere --radius 1 --segments 32 --rings 16 -o ball.stl
+
+# editing (applied in the listed order)
+mesht transform m.obj --center                    # bbox center -> origin
+mesht transform m.obj --mirror x                  # winding auto-corrected
+mesht transform m.obj --scale 2                   # or --scale 1,2,1
+mesht transform m.obj --rotate 0,45,0             # degrees, X then Y then Z
+mesht transform m.obj --translate 0,2,0
+mesht transform m.obj --fit 10                    # largest dimension -> 10 units
+mesht transform m.obj --object wheel --scale 1.2 -o out.obj   # edit one part
+
+mesht merge body.obj wheels.obj -o car.obj        # keeps objects, renames dups
+mesht merge a.stl b.stl --flatten -o one.obj      # single combined object
+mesht convert model.obj -o model.stl              # --ascii for text STL
+```
+
+`-o` picks the output format from the extension. `transform` overwrites
+the input when `-o` is omitted.
+
+## Conventions
+
+- **Axes:** right-handed, **+Y up**, +X right, +Z toward the "front" viewer.
+- Primitives are centered on the origin.
+- Mirroring / negative scaling automatically flips triangle winding so
+  surfaces keep facing outward.
+- `info` reports **volume only for watertight meshes** — otherwise it
+  tells you how many boundary/non-manifold edges the mesh has.
+
+## How an agent should edit a model
+
+1. `mesht info m.obj` — learn size, orientation and object names.
+2. `mesht view m.obj` — see the shape (front/side/top; add `iso` for depth).
+3. Apply **one small transform**, write to a new file.
+4. `mesht view` again and compare — verify before continuing.
+
+The ASCII views are z-buffered orthographic renders; brightness = how
+much the surface faces the light over the viewer's shoulder, so shape
+and curvature read directly from the text. Each view header repeats the
+axis legend and model dimensions.
+
+Example (a 32-segment sphere, front view, width 48):
+
+```
+front view — X→right Y↑up (seen from +Z)
+model 2 x 2 x 2 (XYZ)
+           ==++**####%%%%%%%%%%%%###*
+        -==++**######%%%%%%%%%%%%%%####*
+      :-=+++**#######%%%%%%%%%%%%%%%%%%#**
+     -==++***#######%%%%%%%%%%%%%%%%%%%%##*
+  .:--+++***########%%%%%%%%%%%%%%%%%%%%%%##*+
+```
+
+## Viewing the results as a human
+
+Any of these (Arch/Garuda):
+
+```bash
+sudo pacman -S f3d        # fast minimal viewer:  f3d model.obj
+sudo pacman -S blender    # full editor
+flatpak install org.prusa3d.PrusaSlicer   # if you also want to print
+```

mesh-tool/go.mod

@@ -0,0 +1,3 @@
+module gitea.brasse-pc.eu/brasse/agent-tools/mesh-tool
+
+go 1.24

mesh-tool/main.go

@@ -0,0 +1,406 @@
+// mesht creates, inspects and edits 3D models (OBJ and STL) from the
+// command line, with ASCII multi-view rendering so agents can "see"
+// a model before and after editing it.
+package main
+
+import (
+	"flag"
+	"fmt"
+	"math"
+	"os"
+	"strconv"
+	"strings"
+
+	"gitea.brasse-pc.eu/brasse/agent-tools/mesh-tool/mesh"
+)
+
+var version = "dev"
+
+const usage = `mesht - 3D model tool for agents (OBJ + STL)
+
+Usage:
+  mesht info <file>                     stats: size, volume, watertightness
+  mesht view <file> [flags]             ASCII render from several angles
+  mesht create <primitive> [flags]      box|sphere|cylinder|cone|plane|torus
+  mesht transform <file> [flags]        scale/rotate/translate/mirror/center/fit
+  mesht merge <a> <b> ... -o <out>      combine several files into one
+  mesht convert <in> -o <out>           obj <-> stl
+  mesht version
+
+View flags:
+  --views front,side,top,iso,back       which views to draw (default front,side,top)
+  --width <n>                           characters per view (default 64)
+  --object <name>                       only draw one object from the file
+
+Create flags (always with -o <out.obj|out.stl>):
+  box:      --size x,y,z          (default 1,1,1)
+  sphere:   --radius r --segments n --rings n     (default 1, 24, 12)
+  cylinder: --radius r --height h --segments n    (default 0.5, 1, 24)
+  cone:     --radius r --height h --segments n    (default 0.5, 1, 24)
+  plane:    --size w,d            (default 1,1)
+  torus:    --radius R --tube r --segments n --rings n (default 1, 0.25, 24, 12)
+  --name <s>                      object name in the output
+
+Transform flags (applied in this order):
+  --center                 move bounding-box center to the origin
+  --mirror x|y|z           mirror across that axis' plane
+  --scale s | x,y,z        uniform or per-axis scale
+  --rotate x,y,z           degrees around X, then Y, then Z
+  --translate x,y,z        move
+  --fit n                  uniformly scale so the largest dimension = n
+  --object <name>          only transform the named object (obj files)
+  -o <out>                 output file (default: overwrite input)
+
+Common:
+  --ascii                  write text STL instead of binary
+  Formats are picked from file extensions (.obj, .stl).
+
+Axes: +Y is up, +X right, +Z toward the front viewer (right-handed).
+`
+
+func main() {
+	if len(os.Args) < 2 {
+		fmt.Print(usage)
+		os.Exit(2)
+	}
+	switch os.Args[1] {
+	case "info":
+		cmdInfo(os.Args[2:])
+	case "view":
+		cmdView(os.Args[2:])
+	case "create":
+		cmdCreate(os.Args[2:])
+	case "transform":
+		cmdTransform(os.Args[2:])
+	case "merge":
+		cmdMerge(os.Args[2:])
+	case "convert":
+		cmdConvert(os.Args[2:])
+	case "version", "--version", "-v":
+		fmt.Println("mesht", version)
+	case "help", "--help", "-h":
+		fmt.Print(usage)
+	default:
+		die("unknown command %q — run 'mesht help'", os.Args[1])
+	}
+}
+
+// parseInterspersed lets flags appear before or after positional args.
+func parseInterspersed(fs *flag.FlagSet, args []string) {
+	var flags, pos []string
+	for i := 0; i < len(args); i++ {
+		a := args[i]
+		if len(a) > 1 && a[0] == '-' {
+			flags = append(flags, a)
+			name := strings.TrimLeft(a, "-")
+			if !strings.Contains(name, "=") {
+				f := fs.Lookup(name)
+				isBool := false
+				if f != nil {
+					if bv, ok := f.Value.(interface{ IsBoolFlag() bool }); ok && bv.IsBoolFlag() {
+						isBool = true
+					}
+				}
+				if !isBool && i+1 < len(args) {
+					i++
+					flags = append(flags, args[i])
+				}
+			}
+		} else {
+			pos = append(pos, a)
+		}
+	}
+	fs.Parse(append(flags, pos...))
+}
+
+func parseVec(s string, uniformOK bool) (mesh.Vec3, error) {
+	parts := strings.Split(s, ",")
+	switch len(parts) {
+	case 1:
+		if !uniformOK {
+			return mesh.Vec3{}, fmt.Errorf("%q: want x,y,z", s)
+		}
+		v, err := strconv.ParseFloat(strings.TrimSpace(parts[0]), 64)
+		return mesh.Vec3{X: v, Y: v, Z: v}, err
+	case 3:
+		var v [3]float64
+		for i, p := range parts {
+			f, err := strconv.ParseFloat(strings.TrimSpace(p), 64)
+			if err != nil {
+				return mesh.Vec3{}, fmt.Errorf("%q: bad number %q", s, p)
+			}
+			v[i] = f
+		}
+		return mesh.Vec3{X: v[0], Y: v[1], Z: v[2]}, nil
+	}
+	return mesh.Vec3{}, fmt.Errorf("%q: want one value or x,y,z", s)
+}
+
+func cmdInfo(args []string) {
+	if len(args) != 1 {
+		die("info takes exactly one file")
+	}
+	scene, err := mesh.ReadFile(args[0])
+	if err != nil {
+		die("%v", err)
+	}
+	merged := scene.Merged()
+	mn, mx := merged.BBox()
+	size := mx.Sub(mn)
+	center := mn.Add(size.Mul(0.5))
+	fmt.Printf("file:     %s\n", args[0])
+	fmt.Printf("objects:  %d\n", len(scene.Meshes))
+	fmt.Printf("verts:    %d\n", scene.TotalVerts())
+	fmt.Printf("tris:     %d\n", scene.TotalTris())
+	fmt.Printf("bbox min: (%.4g, %.4g, %.4g)\n", mn.X, mn.Y, mn.Z)
+	fmt.Printf("bbox max: (%.4g, %.4g, %.4g)\n", mx.X, mx.Y, mx.Z)
+	fmt.Printf("size:     %.4g x %.4g x %.4g (X Y Z)\n", size.X, size.Y, size.Z)
+	fmt.Printf("center:   (%.4g, %.4g, %.4g)\n", center.X, center.Y, center.Z)
+	fmt.Printf("area:     %.6g\n", merged.SurfaceArea())
+	if b, nm := merged.EdgeStats(); b == 0 && nm == 0 {
+		fmt.Printf("volume:   %.6g (closed mesh)\n", merged.Volume())
+	} else {
+		fmt.Printf("volume:   n/a (open mesh: %d boundary edges, %d non-manifold edges)\n", b, nm)
+	}
+	if len(scene.Meshes) > 1 {
+		fmt.Println("per object:")
+		for _, m := range scene.Meshes {
+			closed := "open"
+			if m.Closed() {
+				closed = "closed"
+			}
+			fmt.Printf("  %-24s %7d verts %7d tris  %s\n", m.Name, len(m.Verts), len(m.Tris), closed)
+		}
+	}
+}
+
+func cmdView(args []string) {
+	fs := flag.NewFlagSet("view", flag.ExitOnError)
+	views := fs.String("views", "front,side,top", "comma-separated view list")
+	width := fs.Int("width", 64, "characters per view")
+	object := fs.String("object", "", "only draw this object")
+	parseInterspersed(fs, args)
+	if fs.NArg() != 1 {
+		die("view takes exactly one file")
+	}
+	scene, err := mesh.ReadFile(fs.Arg(0))
+	if err != nil {
+		die("%v", err)
+	}
+	m := scene.Merged()
+	if *object != "" {
+		if m = scene.Mesh(*object); m == nil {
+			die("no object named %q in %s (use 'mesht info' to list)", *object, fs.Arg(0))
+		}
+	}
+	for _, name := range strings.Split(*views, ",") {
+		name = strings.TrimSpace(strings.ToLower(name))
+		v, ok := mesh.Views[name]
+		if !ok {
+			die("unknown view %q (available: %s)", name, strings.Join(mesh.ViewOrder, ", "))
+		}
+		fmt.Println(mesh.RenderASCII(m, v, *width))
+	}
+}
+
+func cmdCreate(args []string) {
+	if len(args) < 1 {
+		die("create needs a primitive: box, sphere, cylinder, cone, plane, torus")
+	}
+	prim := args[0]
+	fs := flag.NewFlagSet("create", flag.ExitOnError)
+	size := fs.String("size", "1,1,1", "box/plane size")
+	radius := fs.Float64("radius", 0, "radius")
+	tube := fs.Float64("tube", 0.25, "torus tube radius")
+	height := fs.Float64("height", 1, "height")
+	segments := fs.Int("segments", 24, "segments around")
+	rings := fs.Int("rings", 12, "rings (sphere/torus)")
+	name := fs.String("name", "", "object name")
+	out := fs.String("o", "", "output file (.obj or .stl)")
+	ascii := fs.Bool("ascii", false, "write text STL")
+	parseInterspersed(fs, args[1:])
+	if *out == "" {
+		die("create needs -o <out.obj|out.stl>")
+	}
+	var m *mesh.Mesh
+	switch prim {
+	case "box":
+		sz, err := parseVec(*size, true)
+		if err != nil {
+			die("--size: %v", err)
+		}
+		m = mesh.Box(sz)
+	case "sphere":
+		m = mesh.Sphere(defRadius(*radius, 1), *segments, *rings)
+	case "cylinder":
+		m = mesh.Cylinder(defRadius(*radius, 0.5), *height, *segments)
+	case "cone":
+		m = mesh.Cone(defRadius(*radius, 0.5), *height, *segments)
+	case "plane":
+		sz, err := parseVec(*size, true)
+		if err != nil {
+			die("--size: %v", err)
+		}
+		m = mesh.Plane(sz.X, sz.Z)
+	case "torus":
+		m = mesh.Torus(defRadius(*radius, 1), *tube, *segments, *rings)
+	default:
+		die("unknown primitive %q", prim)
+	}
+	if *name != "" {
+		m.Name = *name
+	}
+	scene := &mesh.Scene{Meshes: []*mesh.Mesh{m}}
+	if err := mesh.WriteFile(*out, scene, *ascii); err != nil {
+		die("%v", err)
+	}
+	fmt.Printf("%s  (%s: %d verts, %d tris)\n", *out, m.Name, len(m.Verts), len(m.Tris))
+}
+
+func defRadius(r, def float64) float64 {
+	if r <= 0 {
+		return def
+	}
+	return r
+}
+
+func cmdTransform(args []string) {
+	fs := flag.NewFlagSet("transform", flag.ExitOnError)
+	center := fs.Bool("center", false, "move bbox center to origin")
+	mirror := fs.String("mirror", "", "x|y|z")
+	scale := fs.String("scale", "", "s or x,y,z")
+	rotate := fs.String("rotate", "", "degrees x,y,z")
+	translate := fs.String("translate", "", "x,y,z")
+	fit := fs.Float64("fit", 0, "scale so the largest dimension equals this")
+	object := fs.String("object", "", "only transform this object")
+	out := fs.String("o", "", "output file (default: overwrite input)")
+	ascii := fs.Bool("ascii", false, "write text STL")
+	parseInterspersed(fs, args)
+	if fs.NArg() != 1 {
+		die("transform takes exactly one file")
+	}
+	in := fs.Arg(0)
+	scene, err := mesh.ReadFile(in)
+	if err != nil {
+		die("%v", err)
+	}
+	targets := scene.Meshes
+	if *object != "" {
+		m := scene.Mesh(*object)
+		if m == nil {
+			die("no object named %q in %s (use 'mesht info' to list)", *object, in)
+		}
+		targets = []*mesh.Mesh{m}
+	}
+
+	if *center {
+		mn, mx := mesh.SceneBBox(targets)
+		c := mn.Add(mx.Sub(mn).Mul(0.5))
+		mesh.ApplyAll(targets, mesh.Translate(c.Mul(-1)))
+	}
+	if *mirror != "" {
+		s := mesh.Vec3{X: 1, Y: 1, Z: 1}
+		switch strings.ToLower(*mirror) {
+		case "x":
+			s.X = -1
+		case "y":
+			s.Y = -1
+		case "z":
+			s.Z = -1
+		default:
+			die("--mirror must be x, y or z")
+		}
+		mesh.ApplyAll(targets, mesh.ScaleXYZ(s))
+	}
+	if *scale != "" {
+		v, err := parseVec(*scale, true)
+		if err != nil {
+			die("--scale: %v", err)
+		}
+		mesh.ApplyAll(targets, mesh.ScaleXYZ(v))
+	}
+	if *rotate != "" {
+		v, err := parseVec(*rotate, false)
+		if err != nil {
+			die("--rotate: %v", err)
+		}
+		rot := mesh.RotateZ(v.Z).Mul(mesh.RotateY(v.Y)).Mul(mesh.RotateX(v.X))
+		mesh.ApplyAll(targets, rot)
+	}
+	if *translate != "" {
+		v, err := parseVec(*translate, false)
+		if err != nil {
+			die("--translate: %v", err)
+		}
+		mesh.ApplyAll(targets, mesh.Translate(v))
+	}
+	if *fit > 0 {
+		mn, mx := mesh.SceneBBox(targets)
+		size := mx.Sub(mn)
+		longest := math.Max(size.X, math.Max(size.Y, size.Z))
+		if longest > 0 {
+			f := *fit / longest
+			mesh.ApplyAll(targets, mesh.ScaleXYZ(mesh.Vec3{X: f, Y: f, Z: f}))
+		}
+	}
+
+	if *out == "" {
+		*out = in
+	}
+	if err := mesh.WriteFile(*out, scene, *ascii); err != nil {
+		die("%v", err)
+	}
+	fmt.Printf("%s  (%d objects, %d verts, %d tris)\n", *out, len(scene.Meshes), scene.TotalVerts(), scene.TotalTris())
+}
+
+func cmdMerge(args []string) {
+	fs := flag.NewFlagSet("merge", flag.ExitOnError)
+	out := fs.String("o", "", "output file")
+	flatten := fs.Bool("flatten", false, "merge everything into a single object")
+	ascii := fs.Bool("ascii", false, "write text STL")
+	parseInterspersed(fs, args)
+	if fs.NArg() < 2 {
+		die("merge needs at least two input files")
+	}
+	if *out == "" {
+		die("merge needs -o <out>")
+	}
+	scene := &mesh.Scene{}
+	for _, path := range fs.Args() {
+		s, err := mesh.ReadFile(path)
+		if err != nil {
+			die("%v", err)
+		}
+		scene.Append(s)
+	}
+	if *flatten {
+		scene = &mesh.Scene{Meshes: []*mesh.Mesh{scene.Merged()}}
+	}
+	if err := mesh.WriteFile(*out, scene, *ascii); err != nil {
+		die("%v", err)
+	}
+	fmt.Printf("%s  (%d objects, %d verts, %d tris)\n", *out, len(scene.Meshes), scene.TotalVerts(), scene.TotalTris())
+}
+
+func cmdConvert(args []string) {
+	fs := flag.NewFlagSet("convert", flag.ExitOnError)
+	out := fs.String("o", "", "output file")
+	ascii := fs.Bool("ascii", false, "write text STL")
+	parseInterspersed(fs, args)
+	if fs.NArg() != 1 || *out == "" {
+		die("convert takes one input file and -o <out>")
+	}
+	scene, err := mesh.ReadFile(fs.Arg(0))
+	if err != nil {
+		die("%v", err)
+	}
+	if err := mesh.WriteFile(*out, scene, *ascii); err != nil {
+		die("%v", err)
+	}
+	fmt.Printf("%s  (%d objects, %d verts, %d tris)\n", *out, len(scene.Meshes), scene.TotalVerts(), scene.TotalTris())
+}
+
+func die(format string, a ...any) {
+	fmt.Fprintf(os.Stderr, "mesht: "+format+"\n", a...)
+	os.Exit(1)
+}

mesh-tool/mesh/ascii.go

@@ -0,0 +1,169 @@
+package mesh
+
+import (
+	"fmt"
+	"math"
+	"strings"
+)
+
+// View is an orthographic camera basis: Right/Up span the screen plane,
+// Toward points from the scene toward the viewer (bigger depth = closer).
+type View struct {
+	Name              string
+	Axes              string // human-readable axis legend
+	Right, Up, Toward Vec3
+}
+
+var Views = map[string]View{
+	"front": {"front", "X→right Y↑up (seen from +Z)", Vec3{1, 0, 0}, Vec3{0, 1, 0}, Vec3{0, 0, 1}},
+	"back":  {"back", "-X→right Y↑up (seen from -Z)", Vec3{-1, 0, 0}, Vec3{0, 1, 0}, Vec3{0, 0, -1}},
+	"side":  {"side", "-Z→right Y↑up (seen from +X)", Vec3{0, 0, -1}, Vec3{0, 1, 0}, Vec3{1, 0, 0}},
+	"top":   {"top", "X→right Z↓down-screen (seen from above, +Y)", Vec3{1, 0, 0}, Vec3{0, 0, -1}, Vec3{0, 1, 0}},
+	"iso": {"iso", "isometric from (+X +Y +Z)",
+		Vec3{1, 0, -1}.Norm(), Vec3{-1, 2, -1}.Norm(), Vec3{1, 1, 1}.Norm()},
+}
+
+// ViewOrder is the canonical ordering for multi-view output.
+var ViewOrder = []string{"front", "side", "top", "iso", "back"}
+
+const shadeRamp = " .:-=+*#%@"
+
+// charAspect compensates terminal cells being ~2x taller than wide.
+const charAspect = 0.5
+
+// RenderASCII draws the mesh from the given view into a text block of
+// the given character width. Triangles are z-buffer rasterized and
+// shaded by how much each face points toward the light (over the
+// viewer's shoulder), so curvature and depth read as brightness.
+func RenderASCII(m *Mesh, v View, width int) string {
+	if width < 8 {
+		width = 8
+	}
+	if len(m.Tris) == 0 {
+		return "(empty mesh)\n"
+	}
+
+	// project all vertices into view space
+	type pv struct{ x, y, z float64 }
+	pts := make([]pv, len(m.Verts))
+	minX, minY := math.Inf(1), math.Inf(1)
+	maxX, maxY := math.Inf(-1), math.Inf(-1)
+	for i, w := range m.Verts {
+		p := pv{w.Dot(v.Right), w.Dot(v.Up), w.Dot(v.Toward)}
+		pts[i] = p
+		minX, maxX = math.Min(minX, p.x), math.Max(maxX, p.x)
+		minY, maxY = math.Min(minY, p.y), math.Max(maxY, p.y)
+	}
+	spanX, spanY := maxX-minX, maxY-minY
+	if spanX == 0 {
+		spanX = 1e-9
+	}
+	if spanY == 0 {
+		spanY = 1e-9
+	}
+	height := int(float64(width) * (spanY / spanX) * charAspect)
+	if height < 1 {
+		height = 1
+	}
+	if height > 4*width {
+		height = 4 * width
+	}
+	sx := float64(width-1) / spanX
+	sy := float64(height-1) / spanY
+
+	depth := make([]float64, width*height)
+	for i := range depth {
+		depth[i] = math.Inf(-1)
+	}
+	shade := make([]float64, width*height)
+	for i := range shade {
+		shade[i] = -1
+	}
+
+	light := v.Toward.Mul(0.8).Add(v.Up.Mul(0.5)).Add(v.Right.Mul(0.3)).Norm()
+
+	for ti, t := range m.Tris {
+		n := m.FaceNormal(ti)
+		// abs: downloaded models often have mixed winding; treat both
+		// sides as lit so the silhouette never goes black
+		lum := 0.15 + 0.85*math.Abs(n.Dot(light))
+
+		a, b, c := pts[t[0]], pts[t[1]], pts[t[2]]
+		ax, ay := (a.x-minX)*sx, (maxY-a.y)*sy
+		bx, by := (b.x-minX)*sx, (maxY-b.y)*sy
+		cx, cy := (c.x-minX)*sx, (maxY-c.y)*sy
+
+		x0 := int(math.Floor(math.Min(ax, math.Min(bx, cx))))
+		x1 := int(math.Ceil(math.Max(ax, math.Max(bx, cx))))
+		y0 := int(math.Floor(math.Min(ay, math.Min(by, cy))))
+		y1 := int(math.Ceil(math.Max(ay, math.Max(by, cy))))
+		if x0 < 0 {
+			x0 = 0
+		}
+		if y0 < 0 {
+			y0 = 0
+		}
+		if x1 >= width {
+			x1 = width - 1
+		}
+		if y1 >= height {
+			y1 = height - 1
+		}
+
+		area := (bx-ax)*(cy-ay) - (by-ay)*(cx-ax)
+		if area == 0 {
+			continue
+		}
+		for py := y0; py <= y1; py++ {
+			for px := x0; px <= x1; px++ {
+				fx, fy := float64(px), float64(py)
+				w0 := (bx-ax)*(fy-ay) - (by-ay)*(fx-ax)
+				w1 := (cx-bx)*(fy-by) - (cy-by)*(fx-bx)
+				w2 := (ax-cx)*(fy-cy) - (ay-cy)*(fx-cx)
+				if !sameSide(w0, w1, w2, area) {
+					continue
+				}
+				// barycentric depth: w2 tracks b, w0 tracks c
+				l1 := w2 / area
+				l2 := w0 / area
+				l0 := 1 - l1 - l2
+				z := l0*a.z + l1*b.z + l2*c.z
+				idx := py*width + px
+				if z > depth[idx] {
+					depth[idx] = z
+					shade[idx] = lum
+				}
+			}
+		}
+	}
+
+	var sb strings.Builder
+	mn, mx := m.BBox()
+	size := mx.Sub(mn)
+	fmt.Fprintf(&sb, "%s view — %s\nmodel %.3g x %.3g x %.3g (XYZ)\n",
+		v.Name, v.Axes, size.X, size.Y, size.Z)
+	ramp := []rune(shadeRamp)
+	for py := 0; py < height; py++ {
+		for px := 0; px < width; px++ {
+			s := shade[py*width+px]
+			if s < 0 {
+				sb.WriteByte(' ')
+				continue
+			}
+			i := int(s * float64(len(ramp)-1))
+			if i >= len(ramp) {
+				i = len(ramp) - 1
+			}
+			sb.WriteRune(ramp[i])
+		}
+		sb.WriteByte('\n')
+	}
+	return sb.String()
+}
+
+func sameSide(w0, w1, w2, area float64) bool {
+	if area > 0 {
+		return w0 >= 0 && w1 >= 0 && w2 >= 0
+	}
+	return w0 <= 0 && w1 <= 0 && w2 <= 0
+}

mesh-tool/mesh/measure.go

@@ -0,0 +1,59 @@
+package mesh
+
+import "math"
+
+// BBox returns the axis-aligned bounding box of the mesh.
+func (m *Mesh) BBox() (min, max Vec3) {
+	if len(m.Verts) == 0 {
+		return Vec3{}, Vec3{}
+	}
+	min, max = m.Verts[0], m.Verts[0]
+	for _, v := range m.Verts[1:] {
+		min = min.Min(v)
+		max = max.Max(v)
+	}
+	return
+}
+
+// SurfaceArea sums the area of all triangles.
+func (m *Mesh) SurfaceArea() float64 {
+	sum := 0.0
+	for _, t := range m.Tris {
+		a, b, c := m.Verts[t[0]], m.Verts[t[1]], m.Verts[t[2]]
+		sum += b.Sub(a).Cross(c.Sub(a)).Len() / 2
+	}
+	return sum
+}
+
+// SignedVolume computes the enclosed volume via the divergence theorem.
+// Only meaningful for closed meshes; positive when windings face outward.
+func (m *Mesh) SignedVolume() float64 {
+	sum := 0.0
+	for _, t := range m.Tris {
+		a, b, c := m.Verts[t[0]], m.Verts[t[1]], m.Verts[t[2]]
+		sum += a.Dot(b.Cross(c))
+	}
+	return sum / 6
+}
+
+// Volume is the absolute enclosed volume.
+func (m *Mesh) Volume() float64 { return math.Abs(m.SignedVolume()) }
+
+// SceneBBox returns the bounding box over the given meshes.
+func SceneBBox(meshes []*Mesh) (min, max Vec3) {
+	first := true
+	for _, m := range meshes {
+		if len(m.Verts) == 0 {
+			continue
+		}
+		mn, mx := m.BBox()
+		if first {
+			min, max = mn, mx
+			first = false
+		} else {
+			min = min.Min(mn)
+			max = max.Max(mx)
+		}
+	}
+	return
+}

mesh-tool/mesh/mesh.go

@@ -0,0 +1,129 @@
+package mesh
+
+import "fmt"
+
+// Triangle indexes three vertices, counter-clockwise seen from outside.
+type Triangle [3]int
+
+// Mesh is one named object: a triangle soup over a shared vertex list.
+type Mesh struct {
+	Name  string
+	Verts []Vec3
+	Tris  []Triangle
+}
+
+// Scene is an ordered list of meshes, matching OBJ objects. STL files
+// load as a single-mesh scene.
+type Scene struct {
+	Meshes []*Mesh
+}
+
+func (s *Scene) TotalVerts() int {
+	n := 0
+	for _, m := range s.Meshes {
+		n += len(m.Verts)
+	}
+	return n
+}
+
+func (s *Scene) TotalTris() int {
+	n := 0
+	for _, m := range s.Meshes {
+		n += len(m.Tris)
+	}
+	return n
+}
+
+// Mesh returns the named mesh, or nil.
+func (s *Scene) Mesh(name string) *Mesh {
+	for _, m := range s.Meshes {
+		if m.Name == name {
+			return m
+		}
+	}
+	return nil
+}
+
+// Merged flattens the scene into a single mesh (copies data).
+func (s *Scene) Merged() *Mesh {
+	out := &Mesh{Name: "merged"}
+	for _, m := range s.Meshes {
+		off := len(out.Verts)
+		out.Verts = append(out.Verts, m.Verts...)
+		for _, t := range m.Tris {
+			out.Tris = append(out.Tris, Triangle{t[0] + off, t[1] + off, t[2] + off})
+		}
+	}
+	if len(s.Meshes) == 1 {
+		out.Name = s.Meshes[0].Name
+	}
+	return out
+}
+
+// Append adds meshes from another scene, de-duplicating names by
+// appending _2, _3, ...
+func (s *Scene) Append(other *Scene) {
+	taken := map[string]bool{}
+	for _, m := range s.Meshes {
+		taken[m.Name] = true
+	}
+	for _, m := range other.Meshes {
+		name := m.Name
+		for i := 2; taken[name]; i++ {
+			name = fmt.Sprintf("%s_%d", m.Name, i)
+		}
+		m.Name = name
+		taken[name] = true
+		s.Meshes = append(s.Meshes, m)
+	}
+}
+
+// FaceNormal returns the (unit) normal of triangle i.
+func (m *Mesh) FaceNormal(i int) Vec3 {
+	t := m.Tris[i]
+	a, b, c := m.Verts[t[0]], m.Verts[t[1]], m.Verts[t[2]]
+	return b.Sub(a).Cross(c.Sub(a)).Norm()
+}
+
+// FlipWinding reverses the orientation of every triangle.
+func (m *Mesh) FlipWinding() {
+	for i, t := range m.Tris {
+		m.Tris[i] = Triangle{t[0], t[2], t[1]}
+	}
+}
+
+type edge struct{ a, b int }
+
+func normEdge(a, b int) edge {
+	if a > b {
+		a, b = b, a
+	}
+	return edge{a, b}
+}
+
+// EdgeStats classifies the mesh topology: boundary edges belong to one
+// triangle, manifold edges to two, anything more is non-manifold. A
+// closed (watertight) mesh has zero boundary and zero non-manifold edges.
+func (m *Mesh) EdgeStats() (boundary, nonManifold int) {
+	count := map[edge]int{}
+	for _, t := range m.Tris {
+		count[normEdge(t[0], t[1])]++
+		count[normEdge(t[1], t[2])]++
+		count[normEdge(t[2], t[0])]++
+	}
+	for _, n := range count {
+		switch {
+		case n == 1:
+			boundary++
+		case n > 2:
+			nonManifold++
+		}
+	}
+	return
+}
+
+// Closed reports whether the mesh is watertight.
+func (m *Mesh) Closed() bool {
+	b, nm := m.EdgeStats()
+	return b == 0 && nm == 0
+}

mesh-tool/mesh/mesh_test.go

@@ -0,0 +1,184 @@
+package mesh
+
+import (
+	"bytes"
+	"math"
+	"strings"
+	"testing"
+)
+
+func almost(t *testing.T, name string, got, want, tol float64) {
+	t.Helper()
+	if math.Abs(got-want) > tol {
+		t.Errorf("%s = %g, want %g (±%g)", name, got, want, tol)
+	}
+}
+
+func TestPrimitiveVolumes(t *testing.T) {
+	box := Box(Vec3{1, 2, 3})
+	almost(t, "box volume", box.SignedVolume(), 6, 1e-9)
+	almost(t, "box area", box.SurfaceArea(), 22, 1e-9)
+	if !box.Closed() {
+		t.Error("box should be watertight")
+	}
+
+	sph := Sphere(1, 64, 32)
+	almost(t, "sphere volume", sph.SignedVolume(), 4*math.Pi/3, 0.07)
+	almost(t, "sphere area", sph.SurfaceArea(), 4*math.Pi, 0.15)
+	if !sph.Closed() {
+		t.Error("sphere should be watertight")
+	}
+
+	cyl := Cylinder(0.5, 2, 64)
+	almost(t, "cylinder volume", cyl.SignedVolume(), math.Pi*0.25*2, 0.01)
+	if !cyl.Closed() {
+		t.Error("cylinder should be watertight")
+	}
+
+	cone := Cone(1, 3, 64)
+	almost(t, "cone volume", cone.SignedVolume(), math.Pi/3*3, 0.02)
+	if !cone.Closed() {
+		t.Error("cone should be watertight")
+	}
+
+	tor := Torus(2, 0.5, 64, 32)
+	almost(t, "torus volume", tor.SignedVolume(), 2*math.Pi*math.Pi*2*0.25, 0.25)
+	if !tor.Closed() {
+		t.Error("torus should be watertight")
+	}
+}
+
+func TestBBoxAndMeasure(t *testing.T) {
+	box := Box(Vec3{2, 4, 6})
+	mn, mx := box.BBox()
+	if mn != (Vec3{-1, -2, -3}) || mx != (Vec3{1, 2, 3}) {
+		t.Errorf("bbox = %v..%v", mn, mx)
+	}
+}
+
+func TestTransformMirrorKeepsVolumePositive(t *testing.T) {
+	box := Box(Vec3{1, 1, 1})
+	box.Apply(ScaleXYZ(Vec3{-1, 1, 1}))
+	almost(t, "mirrored box volume", box.SignedVolume(), 1, 1e-9)
+	box.Apply(RotateY(45).Mul(RotateX(30)))
+	almost(t, "rotated box volume", box.SignedVolume(), 1, 1e-9)
+	box.Apply(Translate(Vec3{10, -5, 3}))
+	almost(t, "translated box volume", box.SignedVolume(), 1, 1e-6)
+}
+
+func TestOBJRoundTrip(t *testing.T) {
+	scene := &Scene{Meshes: []*Mesh{Box(Vec3{1, 2, 3}), Sphere(1, 8, 4)}}
+	scene.Meshes[0].Name = "crate"
+	scene.Meshes[1].Name = "ball"
+	var buf bytes.Buffer
+	if err := WriteOBJ(&buf, scene); err != nil {
+		t.Fatal(err)
+	}
+	back, err := ReadOBJ(&buf)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(back.Meshes) != 2 {
+		t.Fatalf("got %d meshes, want 2", len(back.Meshes))
+	}
+	if back.Meshes[0].Name != "crate" || back.Meshes[1].Name != "ball" {
+		t.Errorf("names = %q, %q", back.Meshes[0].Name, back.Meshes[1].Name)
+	}
+	almost(t, "roundtrip crate volume", back.Meshes[0].SignedVolume(), 6, 1e-9)
+	if !back.Meshes[1].Closed() {
+		t.Error("roundtripped sphere should stay watertight")
+	}
+}
+
+func TestOBJQuadsAndNegativeIndices(t *testing.T) {
+	src := `
+v 0 0 0
+v 1 0 0
+v 1 1 0
+v 0 1 0
+f 1 2 3 4
+f -4 -3 -2
+`
+	s, err := ReadOBJ(strings.NewReader(src))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := s.TotalTris(); got != 3 {
+		t.Errorf("tris = %d, want 3 (quad fan + one negative-index tri)", got)
+	}
+}
+
+func TestSTLRoundTrips(t *testing.T) {
+	box := Box(Vec3{1, 2, 3})
+	scene := &Scene{Meshes: []*Mesh{box}}
+
+	var bin bytes.Buffer
+	if err := WriteSTLBinary(&bin, scene); err != nil {
+		t.Fatal(err)
+	}
+	back, err := ReadSTL(bytes.NewReader(bin.Bytes()))
+	if err != nil {
+		t.Fatal(err)
+	}
+	m := back.Meshes[0]
+	if len(m.Verts) != 8 {
+		t.Errorf("binary stl weld: %d verts, want 8", len(m.Verts))
+	}
+	almost(t, "binary stl volume", m.SignedVolume(), 6, 1e-6)
+
+	var asc bytes.Buffer
+	if err := WriteSTLAscii(&asc, scene); err != nil {
+		t.Fatal(err)
+	}
+	back2, err := ReadSTL(bytes.NewReader(asc.Bytes()))
+	if err != nil {
+		t.Fatal(err)
+	}
+	almost(t, "ascii stl volume", back2.Meshes[0].SignedVolume(), 6, 1e-6)
+	if !back2.Meshes[0].Closed() {
+		t.Error("ascii stl roundtrip should stay watertight")
+	}
+}
+
+func TestSceneAppendRenames(t *testing.T) {
+	a := &Scene{Meshes: []*Mesh{Box(Vec3{1, 1, 1})}}
+	b := &Scene{Meshes: []*Mesh{Box(Vec3{2, 2, 2})}}
+	a.Append(b)
+	if a.Meshes[0].Name == a.Meshes[1].Name {
+		t.Errorf("duplicate names after append: %q", a.Meshes[0].Name)
+	}
+}
+
+func TestRenderASCII(t *testing.T) {
+	sph := Sphere(1, 32, 16)
+	out := RenderASCII(sph, Views["front"], 40)
+	if !strings.Contains(out, "front view") {
+		t.Errorf("missing header:\n%s", out)
+	}
+	ink := 0
+	for _, r := range out {
+		if strings.ContainsRune(shadeRamp[1:], r) {
+			ink++
+		}
+	}
+	if ink < 100 {
+		t.Errorf("sphere render suspiciously empty (%d shaded cells):\n%s", ink, out)
+	}
+	// a sphere should be roughly as tall as wide after aspect correction
+	lines := strings.Split(strings.TrimRight(out, "\n"), "\n")
+	rows := len(lines) - 2 // minus the two header lines
+	if rows < 15 || rows > 25 {
+		t.Errorf("40-wide sphere should be ~20 rows, got %d", rows)
+	}
+}
+
+func TestEdgeStatsOpenMesh(t *testing.T) {
+	p := Plane(1, 1)
+	if p.Closed() {
+		t.Error("plane must not be watertight")
+	}
+	b, nm := p.EdgeStats()
+	if b != 4 || nm != 0 {
+		t.Errorf("plane edge stats = %d boundary, %d non-manifold; want 4, 0", b, nm)
+	}
+}

mesh-tool/mesh/obj.go

@@ -0,0 +1,203 @@
+package mesh
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"os"
+	"strconv"
+	"strings"
+)
+
+// ReadOBJ parses a Wavefront OBJ file. Vertices (v), objects/groups
+// (o/g) and faces (f) are honored; polygons are fan-triangulated;
+// normals, texture coords and materials are ignored (they are
+// recomputed or irrelevant for geometry editing).
+func ReadOBJ(r io.Reader) (*Scene, error) {
+	var verts []Vec3
+	type objFaces struct {
+		name string
+		tris []Triangle // indices into the global vert list
+	}
+	objs := []*objFaces{}
+	current := func() *objFaces {
+		if len(objs) == 0 {
+			objs = append(objs, &objFaces{name: "default"})
+		}
+		return objs[len(objs)-1]
+	}
+
+	sc := bufio.NewScanner(r)
+	sc.Buffer(make([]byte, 0, 64*1024), 16*1024*1024)
+	lineNo := 0
+	for sc.Scan() {
+		lineNo++
+		line := strings.TrimSpace(sc.Text())
+		if line == "" || strings.HasPrefix(line, "#") {
+			continue
+		}
+		fields := strings.Fields(line)
+		switch fields[0] {
+		case "v":
+			if len(fields) < 4 {
+				return nil, fmt.Errorf("obj line %d: vertex needs x y z", lineNo)
+			}
+			var v Vec3
+			var err error
+			if v.X, err = strconv.ParseFloat(fields[1], 64); err == nil {
+				if v.Y, err = strconv.ParseFloat(fields[2], 64); err == nil {
+					v.Z, err = strconv.ParseFloat(fields[3], 64)
+				}
+			}
+			if err != nil {
+				return nil, fmt.Errorf("obj line %d: bad vertex: %v", lineNo, err)
+			}
+			verts = append(verts, v)
+		case "o", "g":
+			name := "unnamed"
+			if len(fields) > 1 {
+				name = strings.Join(fields[1:], " ")
+			}
+			// only open a new object if the current one has faces
+			if len(objs) > 0 && len(objs[len(objs)-1].tris) == 0 {
+				objs[len(objs)-1].name = name
+			} else {
+				objs = append(objs, &objFaces{name: name})
+			}
+		case "f":
+			if len(fields) < 4 {
+				return nil, fmt.Errorf("obj line %d: face needs at least 3 vertices", lineNo)
+			}
+			idx := make([]int, 0, len(fields)-1)
+			for _, f := range fields[1:] {
+				// "v", "v/vt", "v//vn", "v/vt/vn" — we only need v
+				vs := strings.SplitN(f, "/", 2)[0]
+				i, err := strconv.Atoi(vs)
+				if err != nil {
+					return nil, fmt.Errorf("obj line %d: bad face index %q", lineNo, f)
+				}
+				if i < 0 {
+					i = len(verts) + i // negative = relative to current count
+				} else {
+					i-- // obj is 1-based
+				}
+				if i < 0 || i >= len(verts) {
+					return nil, fmt.Errorf("obj line %d: face index %q out of range (have %d vertices)", lineNo, f, len(verts))
+				}
+				idx = append(idx, i)
+			}
+			o := current()
+			for k := 1; k+1 < len(idx); k++ { // fan triangulation
+				o.tris = append(o.tris, Triangle{idx[0], idx[k], idx[k+1]})
+			}
+		}
+	}
+	if err := sc.Err(); err != nil {
+		return nil, err
+	}
+
+	// Compact the global vertex list into per-mesh local lists.
+	scene := &Scene{}
+	for _, o := range objs {
+		if len(o.tris) == 0 {
+			continue
+		}
+		m := &Mesh{Name: o.name}
+		remap := map[int]int{}
+		for _, t := range o.tris {
+			var lt Triangle
+			for k, gi := range t {
+				li, ok := remap[gi]
+				if !ok {
+					li = len(m.Verts)
+					m.Verts = append(m.Verts, verts[gi])
+					remap[gi] = li
+				}
+				lt[k] = li
+			}
+			m.Tris = append(m.Tris, lt)
+		}
+		scene.Meshes = append(scene.Meshes, m)
+	}
+	if len(scene.Meshes) == 0 {
+		return nil, fmt.Errorf("obj contains no faces")
+	}
+	return scene, nil
+}
+
+// WriteOBJ writes the scene as OBJ, one "o" object per mesh.
+func WriteOBJ(w io.Writer, s *Scene) error {
+	bw := bufio.NewWriter(w)
+	fmt.Fprintln(bw, "# exported by mesht (agent-tools)")
+	offset := 1 // obj indices are global and 1-based
+	for _, m := range s.Meshes {
+		fmt.Fprintf(bw, "o %s\n", m.Name)
+		for _, v := range m.Verts {
+			fmt.Fprintf(bw, "v %g %g %g\n", v.X, v.Y, v.Z)
+		}
+		for _, t := range m.Tris {
+			fmt.Fprintf(bw, "f %d %d %d\n", t[0]+offset, t[1]+offset, t[2]+offset)
+		}
+		offset += len(m.Verts)
+	}
+	return bw.Flush()
+}
+
+// ReadFile loads a scene, picking the format from the file extension
+// (.obj, .stl).
+func ReadFile(path string) (*Scene, error) {
+	f, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+	switch ext(path) {
+	case "obj":
+		s, err := ReadOBJ(f)
+		if err != nil {
+			return nil, fmt.Errorf("%s: %w", path, err)
+		}
+		return s, nil
+	case "stl":
+		s, err := ReadSTL(f)
+		if err != nil {
+			return nil, fmt.Errorf("%s: %w", path, err)
+		}
+		return s, nil
+	}
+	return nil, fmt.Errorf("%s: unsupported format (use .obj or .stl)", path)
+}
+
+// WriteFile saves a scene, picking the format from the file extension.
+// asciiSTL selects text STL instead of the default binary.
+func WriteFile(path string, s *Scene, asciiSTL bool) error {
+	f, err := os.Create(path)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+	switch ext(path) {
+	case "obj":
+		err = WriteOBJ(f, s)
+	case "stl":
+		if asciiSTL {
+			err = WriteSTLAscii(f, s)
+		} else {
+			err = WriteSTLBinary(f, s)
+		}
+	default:
+		err = fmt.Errorf("unsupported output format (use .obj or .stl)")
+	}
+	if err != nil {
+		return fmt.Errorf("%s: %w", path, err)
+	}
+	return f.Close()
+}
+
+func ext(path string) string {
+	i := strings.LastIndex(path, ".")
+	if i < 0 {
+		return ""
+	}
+	return strings.ToLower(path[i+1:])
+}

mesh-tool/mesh/primitives.go

@@ -0,0 +1,179 @@
+package mesh
+
+import "math"
+
+// All primitives are centered at the origin with +Y up and get outward
+// (counter-clockwise) winding; ensureOutward fixes the global
+// orientation via the signed volume as a safety net.
+
+func ensureOutward(m *Mesh) *Mesh {
+	if m.SignedVolume() < 0 {
+		m.FlipWinding()
+	}
+	return m
+}
+
+// Box builds an axis-aligned box of the given size.
+func Box(size Vec3) *Mesh {
+	x, y, z := size.X/2, size.Y/2, size.Z/2
+	m := &Mesh{
+		Name: "box",
+		Verts: []Vec3{
+			{-x, -y, -z}, {x, -y, -z}, {x, y, -z}, {-x, y, -z}, // back  (z-)
+			{-x, -y, z}, {x, -y, z}, {x, y, z}, {-x, y, z}, // front (z+)
+		},
+	}
+	quads := [][4]int{
+		{0, 3, 2, 1}, // back
+		{4, 5, 6, 7}, // front
+		{0, 1, 5, 4}, // bottom
+		{2, 3, 7, 6}, // top
+		{1, 2, 6, 5}, // right
+		{0, 4, 7, 3}, // left
+	}
+	for _, q := range quads {
+		m.Tris = append(m.Tris, Triangle{q[0], q[1], q[2]}, Triangle{q[0], q[2], q[3]})
+	}
+	return ensureOutward(m)
+}
+
+// Plane builds a flat rectangle in the XZ plane (an open mesh).
+func Plane(w, d float64) *Mesh {
+	x, z := w/2, d/2
+	return &Mesh{
+		Name:  "plane",
+		Verts: []Vec3{{-x, 0, -z}, {x, 0, -z}, {x, 0, z}, {-x, 0, z}},
+		Tris:  []Triangle{{0, 2, 1}, {0, 3, 2}}, // +Y facing
+	}
+}
+
+// Sphere builds a UV sphere. segments = around the equator (>= 3),
+// rings = from pole to pole (>= 2).
+func Sphere(r float64, segments, rings int) *Mesh {
+	if segments < 3 {
+		segments = 3
+	}
+	if rings < 2 {
+		rings = 2
+	}
+	m := &Mesh{Name: "sphere"}
+	top := len(m.Verts)
+	m.Verts = append(m.Verts, Vec3{0, r, 0})
+	// interior rings, top to bottom
+	ringStart := make([]int, rings)
+	for i := 1; i < rings; i++ {
+		theta := math.Pi * float64(i) / float64(rings)
+		y := r * math.Cos(theta)
+		rad := r * math.Sin(theta)
+		ringStart[i] = len(m.Verts)
+		for j := 0; j < segments; j++ {
+			phi := 2 * math.Pi * float64(j) / float64(segments)
+			m.Verts = append(m.Verts, Vec3{rad * math.Cos(phi), y, rad * math.Sin(phi)})
+		}
+	}
+	bottom := len(m.Verts)
+	m.Verts = append(m.Verts, Vec3{0, -r, 0})
+
+	at := func(ring, seg int) int { return ringStart[ring] + seg%segments }
+	for j := 0; j < segments; j++ {
+		m.Tris = append(m.Tris, Triangle{top, at(1, j), at(1, j+1)}) // top cap
+		m.Tris = append(m.Tris, Triangle{bottom, at(rings-1, j+1), at(rings-1, j)})
+	}
+	for i := 1; i < rings-1; i++ {
+		for j := 0; j < segments; j++ {
+			a, b := at(i, j), at(i, j+1)
+			c, d := at(i+1, j+1), at(i+1, j)
+			m.Tris = append(m.Tris, Triangle{a, b, c}, Triangle{a, c, d})
+		}
+	}
+	return ensureOutward(m)
+}
+
+// Cylinder builds a closed cylinder of height h around the Y axis.
+func Cylinder(r, h float64, segments int) *Mesh {
+	if segments < 3 {
+		segments = 3
+	}
+	m := &Mesh{Name: "cylinder"}
+	y := h / 2
+	topC := len(m.Verts)
+	m.Verts = append(m.Verts, Vec3{0, y, 0})
+	botC := len(m.Verts)
+	m.Verts = append(m.Verts, Vec3{0, -y, 0})
+	topStart := len(m.Verts)
+	for j := 0; j < segments; j++ {
+		phi := 2 * math.Pi * float64(j) / float64(segments)
+		m.Verts = append(m.Verts, Vec3{r * math.Cos(phi), y, r * math.Sin(phi)})
+	}
+	botStart := len(m.Verts)
+	for j := 0; j < segments; j++ {
+		phi := 2 * math.Pi * float64(j) / float64(segments)
+		m.Verts = append(m.Verts, Vec3{r * math.Cos(phi), -y, r * math.Sin(phi)})
+	}
+	t := func(j int) int { return topStart + j%segments }
+	b := func(j int) int { return botStart + j%segments }
+	for j := 0; j < segments; j++ {
+		m.Tris = append(m.Tris,
+			Triangle{topC, t(j + 1), t(j)},     // top cap
+			Triangle{botC, b(j), b(j + 1)},     // bottom cap
+			Triangle{t(j), t(j + 1), b(j + 1)}, // side
+			Triangle{t(j), b(j + 1), b(j)},     // side
+		)
+	}
+	return ensureOutward(m)
+}
+
+// Cone builds a closed cone with its base at -h/2 and apex at +h/2.
+func Cone(r, h float64, segments int) *Mesh {
+	if segments < 3 {
+		segments = 3
+	}
+	m := &Mesh{Name: "cone"}
+	apex := len(m.Verts)
+	m.Verts = append(m.Verts, Vec3{0, h / 2, 0})
+	baseC := len(m.Verts)
+	m.Verts = append(m.Verts, Vec3{0, -h / 2, 0})
+	start := len(m.Verts)
+	for j := 0; j < segments; j++ {
+		phi := 2 * math.Pi * float64(j) / float64(segments)
+		m.Verts = append(m.Verts, Vec3{r * math.Cos(phi), -h / 2, r * math.Sin(phi)})
+	}
+	at := func(j int) int { return start + j%segments }
+	for j := 0; j < segments; j++ {
+		m.Tris = append(m.Tris,
+			Triangle{apex, at(j + 1), at(j)},
+			Triangle{baseC, at(j), at(j + 1)},
+		)
+	}
+	return ensureOutward(m)
+}
+
+// Torus builds a torus around the Y axis: ring radius R (center of tube
+// to center of torus) and tube radius r.
+func Torus(R, r float64, segments, rings int) *Mesh {
+	if segments < 3 {
+		segments = 3
+	}
+	if rings < 3 {
+		rings = 3
+	}
+	m := &Mesh{Name: "torus"}
+	for i := 0; i < segments; i++ { // around the main ring
+		phi := 2 * math.Pi * float64(i) / float64(segments)
+		cx, cz := math.Cos(phi), math.Sin(phi)
+		for j := 0; j < rings; j++ { // around the tube
+			theta := 2 * math.Pi * float64(j) / float64(rings)
+			rad := R + r*math.Cos(theta)
+			m.Verts = append(m.Verts, Vec3{rad * cx, r * math.Sin(theta), rad * cz})
+		}
+	}
+	at := func(i, j int) int { return (i%segments)*rings + j%rings }
+	for i := 0; i < segments; i++ {
+		for j := 0; j < rings; j++ {
+			a, b := at(i, j), at(i+1, j)
+			c, d := at(i+1, j+1), at(i, j+1)
+			m.Tris = append(m.Tris, Triangle{a, b, c}, Triangle{a, c, d})
+		}
+	}
+	return ensureOutward(m)
+}

mesh-tool/mesh/stl.go

@@ -0,0 +1,182 @@
+package mesh
+
+import (
+	"bufio"
+	"bytes"
+	"encoding/binary"
+	"fmt"
+	"io"
+	"math"
+	"strconv"
+	"strings"
+)
+
+// ReadSTL reads binary or ASCII STL (auto-detected). STL stores loose
+// triangles, so identical vertices are welded back together to recover
+// connectivity (needed for watertight checks and sane OBJ export).
+func ReadSTL(r io.Reader) (*Scene, error) {
+	data, err := io.ReadAll(r)
+	if err != nil {
+		return nil, err
+	}
+	if len(data) >= 84 {
+		n := binary.LittleEndian.Uint32(data[80:84])
+		if int(84+50*n) == len(data) {
+			return readSTLBinary(data)
+		}
+	}
+	if bytes.HasPrefix(bytes.TrimLeft(data, " \t\r\n"), []byte("solid")) {
+		return readSTLAscii(data)
+	}
+	return nil, fmt.Errorf("not a valid STL file (neither binary layout nor 'solid ...' text)")
+}
+
+type welder struct {
+	mesh  *Mesh
+	index map[Vec3]int
+}
+
+func newWelder(name string) *welder {
+	return &welder{mesh: &Mesh{Name: name}, index: map[Vec3]int{}}
+}
+
+func (w *welder) add(a, b, c Vec3) {
+	var t Triangle
+	for i, v := range [3]Vec3{a, b, c} {
+		idx, ok := w.index[v]
+		if !ok {
+			idx = len(w.mesh.Verts)
+			w.mesh.Verts = append(w.mesh.Verts, v)
+			w.index[v] = idx
+		}
+		t[i] = idx
+	}
+	if t[0] == t[1] || t[1] == t[2] || t[2] == t[0] {
+		return // degenerate
+	}
+	w.mesh.Tris = append(w.mesh.Tris, t)
+}
+
+func readSTLBinary(data []byte) (*Scene, error) {
+	n := int(binary.LittleEndian.Uint32(data[80:84]))
+	w := newWelder("stl")
+	off := 84
+	f32 := func(o int) float64 {
+		return float64(math.Float32frombits(binary.LittleEndian.Uint32(data[o : o+4])))
+	}
+	for i := 0; i < n; i++ {
+		// 12 bytes normal (ignored), 3 * 12 bytes vertices, 2 bytes attrs
+		var v [3]Vec3
+		for k := 0; k < 3; k++ {
+			base := off + 12 + k*12
+			v[k] = Vec3{f32(base), f32(base + 4), f32(base + 8)}
+		}
+		w.add(v[0], v[1], v[2])
+		off += 50
+	}
+	return &Scene{Meshes: []*Mesh{w.mesh}}, nil
+}
+
+func readSTLAscii(data []byte) (*Scene, error) {
+	name := "stl"
+	w := newWelder(name)
+	var cur []Vec3
+	sc := bufio.NewScanner(bytes.NewReader(data))
+	sc.Buffer(make([]byte, 0, 64*1024), 16*1024*1024)
+	lineNo := 0
+	for sc.Scan() {
+		lineNo++
+		fields := strings.Fields(sc.Text())
+		if len(fields) == 0 {
+			continue
+		}
+		switch fields[0] {
+		case "solid":
+			if len(fields) > 1 {
+				w.mesh.Name = fields[1]
+			}
+		case "vertex":
+			if len(fields) < 4 {
+				return nil, fmt.Errorf("stl line %d: vertex needs x y z", lineNo)
+			}
+			var v Vec3
+			var err error
+			if v.X, err = strconv.ParseFloat(fields[1], 64); err == nil {
+				if v.Y, err = strconv.ParseFloat(fields[2], 64); err == nil {
+					v.Z, err = strconv.ParseFloat(fields[3], 64)
+				}
+			}
+			if err != nil {
+				return nil, fmt.Errorf("stl line %d: bad vertex: %v", lineNo, err)
+			}
+			cur = append(cur, v)
+		case "endfacet":
+			if len(cur) != 3 {
+				return nil, fmt.Errorf("stl line %d: facet has %d vertices, want 3", lineNo, len(cur))
+			}
+			w.add(cur[0], cur[1], cur[2])
+			cur = cur[:0]
+		}
+	}
+	if err := sc.Err(); err != nil {
+		return nil, err
+	}
+	if len(w.mesh.Tris) == 0 {
+		return nil, fmt.Errorf("stl contains no triangles")
+	}
+	return &Scene{Meshes: []*Mesh{w.mesh}}, nil
+}
+
+// WriteSTLBinary writes the whole scene as one binary STL solid
+// (STL has no concept of multiple named objects).
+func WriteSTLBinary(w io.Writer, s *Scene) error {
+	m := s.Merged()
+	bw := bufio.NewWriter(w)
+	header := make([]byte, 80)
+	copy(header, []byte("exported by mesht (agent-tools)"))
+	bw.Write(header)
+	binary.Write(bw, binary.LittleEndian, uint32(len(m.Tris)))
+	buf := make([]byte, 50)
+	for i, t := range m.Tris {
+		n := m.FaceNormal(i)
+		le := binary.LittleEndian
+		le.PutUint32(buf[0:], math.Float32bits(float32(n.X)))
+		le.PutUint32(buf[4:], math.Float32bits(float32(n.Y)))
+		le.PutUint32(buf[8:], math.Float32bits(float32(n.Z)))
+		for k := 0; k < 3; k++ {
+			v := m.Verts[t[k]]
+			le.PutUint32(buf[12+k*12:], math.Float32bits(float32(v.X)))
+			le.PutUint32(buf[16+k*12:], math.Float32bits(float32(v.Y)))
+			le.PutUint32(buf[20+k*12:], math.Float32bits(float32(v.Z)))
+		}
+		buf[48], buf[49] = 0, 0
+		bw.Write(buf)
+	}
+	return bw.Flush()
+}
+
+// WriteSTLAscii writes the scene as a text STL solid.
+func WriteSTLAscii(w io.Writer, s *Scene) error {
+	m := s.Merged()
+	bw := bufio.NewWriter(w)
+	fmt.Fprintf(bw, "solid %s\n", sanitizeToken(m.Name))
+	for i, t := range m.Tris {
+		n := m.FaceNormal(i)
+		fmt.Fprintf(bw, "  facet normal %g %g %g\n    outer loop\n", n.X, n.Y, n.Z)
+		for k := 0; k < 3; k++ {
+			v := m.Verts[t[k]]
+			fmt.Fprintf(bw, "      vertex %g %g %g\n", v.X, v.Y, v.Z)
+		}
+		fmt.Fprintf(bw, "    endloop\n  endfacet\n")
+	}
+	fmt.Fprintf(bw, "endsolid %s\n", sanitizeToken(m.Name))
+	return bw.Flush()
+}
+
+func sanitizeToken(s string) string {
+	s = strings.ReplaceAll(strings.TrimSpace(s), " ", "_")
+	if s == "" {
+		return "mesh"
+	}
+	return s
+}

mesh-tool/mesh/transform.go

@@ -0,0 +1,20 @@
+package mesh
+
+// Apply transforms every vertex by mat. Mirroring transforms (negative
+// determinant) flip triangle winding, so it is corrected here to keep
+// normals pointing the same way relative to the surface.
+func (m *Mesh) Apply(mat Mat4) {
+	for i := range m.Verts {
+		m.Verts[i] = mat.Apply(m.Verts[i])
+	}
+	if mat.Det3() < 0 {
+		m.FlipWinding()
+	}
+}
+
+// ApplyAll transforms a set of meshes.
+func ApplyAll(meshes []*Mesh, mat Mat4) {
+	for _, m := range meshes {
+		m.Apply(mat)
+	}
+}

mesh-tool/mesh/vec.go

@@ -0,0 +1,122 @@
+package mesh
+
+import "math"
+
+// Vec3 is a point or direction in 3D space.
+type Vec3 struct{ X, Y, Z float64 }
+
+func (a Vec3) Add(b Vec3) Vec3    { return Vec3{a.X + b.X, a.Y + b.Y, a.Z + b.Z} }
+func (a Vec3) Sub(b Vec3) Vec3    { return Vec3{a.X - b.X, a.Y - b.Y, a.Z - b.Z} }
+func (a Vec3) Mul(s float64) Vec3 { return Vec3{a.X * s, a.Y * s, a.Z * s} }
+func (a Vec3) Dot(b Vec3) float64 { return a.X*b.X + a.Y*b.Y + a.Z*b.Z }
+func (a Vec3) Len() float64       { return math.Sqrt(a.Dot(a)) }
+func (a Vec3) Cross(b Vec3) Vec3 {
+	return Vec3{
+		a.Y*b.Z - a.Z*b.Y,
+		a.Z*b.X - a.X*b.Z,
+		a.X*b.Y - a.Y*b.X,
+	}
+}
+
+// Norm returns the unit vector, or the zero vector for zero-length input.
+func (a Vec3) Norm() Vec3 {
+	l := a.Len()
+	if l == 0 {
+		return Vec3{}
+	}
+	return a.Mul(1 / l)
+}
+
+// Min/Max return the component-wise minimum/maximum.
+func (a Vec3) Min(b Vec3) Vec3 {
+	return Vec3{math.Min(a.X, b.X), math.Min(a.Y, b.Y), math.Min(a.Z, b.Z)}
+}
+func (a Vec3) Max(b Vec3) Vec3 {
+	return Vec3{math.Max(a.X, b.X), math.Max(a.Y, b.Y), math.Max(a.Z, b.Z)}
+}
+
+// Mat4 is a row-major 4x4 transform matrix.
+type Mat4 [16]float64
+
+func Identity() Mat4 {
+	return Mat4{
+		1, 0, 0, 0,
+		0, 1, 0, 0,
+		0, 0, 1, 0,
+		0, 0, 0, 1,
+	}
+}
+
+// Mul returns m * n (n is applied first when transforming points).
+func (m Mat4) Mul(n Mat4) Mat4 {
+	var r Mat4
+	for row := 0; row < 4; row++ {
+		for col := 0; col < 4; col++ {
+			sum := 0.0
+			for k := 0; k < 4; k++ {
+				sum += m[row*4+k] * n[k*4+col]
+			}
+			r[row*4+col] = sum
+		}
+	}
+	return r
+}
+
+// Apply transforms a point (w = 1).
+func (m Mat4) Apply(v Vec3) Vec3 {
+	return Vec3{
+		m[0]*v.X + m[1]*v.Y + m[2]*v.Z + m[3],
+		m[4]*v.X + m[5]*v.Y + m[6]*v.Z + m[7],
+		m[8]*v.X + m[9]*v.Y + m[10]*v.Z + m[11],
+	}
+}
+
+// Det3 is the determinant of the upper-left 3x3. Negative means the
+// transform mirrors space, which flips triangle winding.
+func (m Mat4) Det3() float64 {
+	return m[0]*(m[5]*m[10]-m[6]*m[9]) -
+		m[1]*(m[4]*m[10]-m[6]*m[8]) +
+		m[2]*(m[4]*m[9]-m[5]*m[8])
+}
+
+func Translate(t Vec3) Mat4 {
+	m := Identity()
+	m[3], m[7], m[11] = t.X, t.Y, t.Z
+	return m
+}
+
+func ScaleXYZ(s Vec3) Mat4 {
+	m := Identity()
+	m[0], m[5], m[10] = s.X, s.Y, s.Z
+	return m
+}
+
+func RotateX(deg float64) Mat4 {
+	s, c := math.Sincos(deg * math.Pi / 180)
+	return Mat4{
+		1, 0, 0, 0,
+		0, c, -s, 0,
+		0, s, c, 0,
+		0, 0, 0, 1,
+	}
+}
+
+func RotateY(deg float64) Mat4 {
+	s, c := math.Sincos(deg * math.Pi / 180)
+	return Mat4{
+		c, 0, s, 0,
+		0, 1, 0, 0,
+		-s, 0, c, 0,
+		0, 0, 0, 1,
+	}
+}
+
+func RotateZ(deg float64) Mat4 {
+	s, c := math.Sincos(deg * math.Pi / 180)
+	return Mat4{
+		c, -s, 0, 0,
+		s, c, 0, 0,
+		0, 0, 1, 0,
+		0, 0, 0, 1,
+	}
+}

pixel-sprite-maker/README.md

@@ -0,0 +1,86 @@
+# pixel-sprite-maker (`spritec`)
+
+Turns human/agent-readable `.sprite` text files into pixel art (**PNG, JPG, SVG**)
+and combines several sprites into **sprite sheets / animation strips**.
+Written in Go, zero dependencies, single static binary.
+
+## Build
+
+```bash
+# Arch/Garuda: sudo pacman -S go
+cd pixel-sprite-maker
+go build -o build/spritec .        # or run the VS Code task "build pixel-sprite-maker"
+go test ./...
+```
+
+## The `.sprite` format
+
+One file = one sprite. Designed so an agent can *see* the result in the text:
+
+```
+# comment lines start with '#'
+sprite: coin           # optional name
+palette:
+  k = #1A1205    dark outline
+  y = #FFD700    gold
+  Y = gold       CSS names work too — text after the color is a comment
+grid:
+  ..kkkk..
+  .kyyyYk.
+  kyyyYYyk
+  ..kkkk..
+```
+
+Rules:
+
+- **One character = one pixel.** Every grid row must be the same width.
+- Palette keys are exactly one character (any unicode). `#`, `=`, `:` and
+  whitespace are not allowed as keys — so the number of colors is
+  practically unlimited (a-z, A-Z, 0-9, `!@%&*`, unicode…).
+- `.` is **transparent by default**; override it in the palette if you want.
+- Colors: `#RGB`, `#RGBA`, `#RRGGBB`, `#RRGGBBAA`, `rgb(r,g,b)`,
+  `rgba(r,g,b,a)` (alpha 0-255 or 0.0-1.0), all CSS named colors, `none`.
+- Max **256x256** pixels per sprite. Sheets may exceed this; single frames may not.
+
+## Commands
+
+```bash
+spritec render coin.sprite -o coin.png --scale 8      # png/jpg/svg from extension
+spritec render coin.sprite --format svg               # -> coin.svg
+spritec render heart.sprite -o heart.jpg --bg '#222034'  # jpg has no alpha: pick bg
+spritec info coin.sprite                              # validate + palette stats
+spritec preview coin.sprite                           # draw in the terminal (truecolor)
+
+# Sprite sheets / animations — row-major (left→right, then top→bottom):
+spritec sheet walk_1.sprite walk_2.sprite walk_3.sprite walk_4.sprite -o walk           # 1 row
+spritec sheet walk_*.sprite --cols 2 -o walkgrid      # 2D: 2 columns x 2 rows
+```
+
+Flags: `-o` output, `--format png|jpg|svg`, `--scale n` (integer nearest-neighbour
+upscale), `--bg color` + `--quality 1-100` (jpg only), `--cols n` (sheet only).
+
+## Sheet output naming — read the layout from the file name
+
+```
+<name>_<cellW>x<cellH>_<cols>x<rows>.<ext>
+
+walk_8x8_4x1.png   = 8x8 px per frame, 4 columns, 1 row (animation strip)
+tiles_16x16_4x2.png = 16x16 px per frame, 4 columns, 2 rows
+```
+
+Frame order is always **row-major**: index = `row * cols + col`, frame 0 is
+top-left. If the frame count doesn't fill the grid, trailing cells are
+transparent. In game code:
+
+```
+frameX = (index % cols) * cellW
+frameY = (index / cols) * cellH
+```
+
+## Exit codes & errors
+
+`0` on success, `1` on any error, `2` on missing command. Parse errors name
+the exact line/row/column and what was expected, so an agent can fix the
+file without guessing.
+
+Examples live in [`examples/`](examples/); generated output in `examples/out/`.

pixel-sprite-maker/examples/coin.sprite

@@ -0,0 +1,17 @@
+# A small gold coin, 8x8.
+# '.' is transparent by default and never needs a palette entry.
+sprite: coin
+palette:
+  k = #1A1205    dark outline
+  y = #FFD700    gold
+  Y = #FFF3A0    highlight
+  s = #B8860B    shadow
+grid:
+  ..kkkk..
+  .kyyyYk.
+  kyyyYYsk
+  kyyYyysk
+  kyYyyysk
+  kYyyyssk
+  .kysssk.
+  ..kkkk..

pixel-sprite-maker/examples/heart.sprite

@@ -0,0 +1,25 @@
+# A 16x16 heart with shading, shows named colors and rgb().
+sprite: heart
+palette:
+  k = #2B0A10          outline
+  r = crimson          main red
+  R = rgb(255, 90, 110) light red
+  d = #8B1A2B          dark red
+  w = #FFFFFFCC        semi-transparent shine
+grid:
+  ................
+  ..kkk....kkk....
+  .krrRk..kRrrk...
+  krrRRrkkrRrrrk..
+  krRwRrrrrrrrdk..
+  krRwwRrrrrrrdk..
+  krRwRrrrrrrddk..
+  krrRrrrrrrrddk..
+  .krrrrrrrrrdk...
+  ..krrrrrrrdk....
+  ...krrrrrdk.....
+  ....krrrdk......
+  .....krdk.......
+  ......kk........
+  ................
+  ................

pixel-sprite-maker/examples/out/coin.svg

@@ -0,0 +1,34 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="64" height="64" viewBox="0 0 8 8" shape-rendering="crispEdges">
+<rect x="2" y="0" width="4" height="1" fill="#1a1205"/>
+<rect x="1" y="1" width="1" height="1" fill="#1a1205"/>
+<rect x="2" y="1" width="3" height="1" fill="#ffd700"/>
+<rect x="5" y="1" width="1" height="1" fill="#fff3a0"/>
+<rect x="6" y="1" width="1" height="1" fill="#1a1205"/>
+<rect x="0" y="2" width="1" height="1" fill="#1a1205"/>
+<rect x="1" y="2" width="3" height="1" fill="#ffd700"/>
+<rect x="4" y="2" width="2" height="1" fill="#fff3a0"/>
+<rect x="6" y="2" width="1" height="1" fill="#b8860b"/>
+<rect x="7" y="2" width="1" height="1" fill="#1a1205"/>
+<rect x="0" y="3" width="1" height="1" fill="#1a1205"/>
+<rect x="1" y="3" width="2" height="1" fill="#ffd700"/>
+<rect x="3" y="3" width="1" height="1" fill="#fff3a0"/>
+<rect x="4" y="3" width="2" height="1" fill="#ffd700"/>
+<rect x="6" y="3" width="1" height="1" fill="#b8860b"/>
+<rect x="7" y="3" width="1" height="1" fill="#1a1205"/>
+<rect x="0" y="4" width="1" height="1" fill="#1a1205"/>
+<rect x="1" y="4" width="1" height="1" fill="#ffd700"/>
+<rect x="2" y="4" width="1" height="1" fill="#fff3a0"/>
+<rect x="3" y="4" width="3" height="1" fill="#ffd700"/>
+<rect x="6" y="4" width="1" height="1" fill="#b8860b"/>
+<rect x="7" y="4" width="1" height="1" fill="#1a1205"/>
+<rect x="0" y="5" width="1" height="1" fill="#1a1205"/>
+<rect x="1" y="5" width="1" height="1" fill="#fff3a0"/>
+<rect x="2" y="5" width="3" height="1" fill="#ffd700"/>
+<rect x="5" y="5" width="2" height="1" fill="#b8860b"/>
+<rect x="7" y="5" width="1" height="1" fill="#1a1205"/>
+<rect x="1" y="6" width="1" height="1" fill="#1a1205"/>
+<rect x="2" y="6" width="1" height="1" fill="#ffd700"/>
+<rect x="3" y="6" width="3" height="1" fill="#b8860b"/>
+<rect x="6" y="6" width="1" height="1" fill="#1a1205"/>
+<rect x="2" y="7" width="4" height="1" fill="#1a1205"/>
+</svg>

pixel-sprite-maker/examples/out/walkgrid_8x8_2x2.svg

@@ -0,0 +1,57 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" viewBox="0 0 16 16" shape-rendering="crispEdges">
+<rect x="2" y="0" width="3" height="1" fill="#101018"/>
+<rect x="10" y="0" width="3" height="1" fill="#101018"/>
+<rect x="2" y="1" width="1" height="1" fill="#101018"/>
+<rect x="3" y="1" width="2" height="1" fill="#f2c09a"/>
+<rect x="10" y="1" width="1" height="1" fill="#101018"/>
+<rect x="11" y="1" width="2" height="1" fill="#f2c09a"/>
+<rect x="2" y="2" width="1" height="1" fill="#101018"/>
+<rect x="3" y="2" width="2" height="1" fill="#f2c09a"/>
+<rect x="10" y="2" width="1" height="1" fill="#101018"/>
+<rect x="11" y="2" width="2" height="1" fill="#f2c09a"/>
+<rect x="1" y="3" width="1" height="1" fill="#101018"/>
+<rect x="2" y="3" width="3" height="1" fill="#2e5fb7"/>
+<rect x="5" y="3" width="1" height="1" fill="#101018"/>
+<rect x="9" y="3" width="1" height="1" fill="#101018"/>
+<rect x="10" y="3" width="3" height="1" fill="#2e5fb7"/>
+<rect x="13" y="3" width="1" height="1" fill="#101018"/>
+<rect x="2" y="4" width="3" height="1" fill="#2e5fb7"/>
+<rect x="10" y="4" width="3" height="1" fill="#2e5fb7"/>
+<rect x="2" y="5" width="3" height="1" fill="#22406e"/>
+<rect x="10" y="5" width="3" height="1" fill="#22406e"/>
+<rect x="2" y="6" width="1" height="1" fill="#22406e"/>
+<rect x="4" y="6" width="1" height="1" fill="#22406e"/>
+<rect x="9" y="6" width="1" height="1" fill="#22406e"/>
+<rect x="13" y="6" width="1" height="1" fill="#22406e"/>
+<rect x="2" y="7" width="1" height="1" fill="#101018"/>
+<rect x="4" y="7" width="1" height="1" fill="#101018"/>
+<rect x="9" y="7" width="1" height="1" fill="#101018"/>
+<rect x="13" y="7" width="1" height="1" fill="#101018"/>
+<rect x="2" y="8" width="3" height="1" fill="#101018"/>
+<rect x="10" y="8" width="3" height="1" fill="#101018"/>
+<rect x="2" y="9" width="1" height="1" fill="#101018"/>
+<rect x="3" y="9" width="2" height="1" fill="#f2c09a"/>
+<rect x="10" y="9" width="1" height="1" fill="#101018"/>
+<rect x="11" y="9" width="2" height="1" fill="#f2c09a"/>
+<rect x="2" y="10" width="1" height="1" fill="#101018"/>
+<rect x="3" y="10" width="2" height="1" fill="#f2c09a"/>
+<rect x="10" y="10" width="1" height="1" fill="#101018"/>
+<rect x="11" y="10" width="2" height="1" fill="#f2c09a"/>
+<rect x="2" y="11" width="3" height="1" fill="#2e5fb7"/>
+<rect x="5" y="11" width="1" height="1" fill="#101018"/>
+<rect x="9" y="11" width="1" height="1" fill="#101018"/>
+<rect x="10" y="11" width="3" height="1" fill="#2e5fb7"/>
+<rect x="13" y="11" width="1" height="1" fill="#101018"/>
+<rect x="1" y="12" width="1" height="1" fill="#101018"/>
+<rect x="2" y="12" width="3" height="1" fill="#2e5fb7"/>
+<rect x="10" y="12" width="3" height="1" fill="#2e5fb7"/>
+<rect x="2" y="13" width="3" height="1" fill="#22406e"/>
+<rect x="10" y="13" width="3" height="1" fill="#22406e"/>
+<rect x="2" y="14" width="1" height="1" fill="#22406e"/>
+<rect x="4" y="14" width="1" height="1" fill="#22406e"/>
+<rect x="10" y="14" width="2" height="1" fill="#22406e"/>
+<rect x="2" y="15" width="1" height="1" fill="#101018"/>
+<rect x="4" y="15" width="1" height="1" fill="#101018"/>
+<rect x="9" y="15" width="1" height="1" fill="#101018"/>
+<rect x="12" y="15" width="1" height="1" fill="#101018"/>
+</svg>

pixel-sprite-maker/examples/walk_1.sprite

@@ -0,0 +1,16 @@
+# Frame 1/4 of a tiny walking guy, 8x8. Legs together.
+sprite: walk_1
+palette:
+  k = #101018    outline / hair
+  s = #F2C09A    skin
+  b = #2E5FB7    shirt
+  d = #22406E    pants
+grid:
+  ..kkk...
+  ..kss...
+  ..kss...
+  .kbbbk..
+  ..bbb...
+  ..ddd...
+  ..d.d...
+  ..k.k...

pixel-sprite-maker/examples/walk_2.sprite

@@ -0,0 +1,16 @@
+# Frame 2/4 - right leg forward.
+sprite: walk_2
+palette:
+  k = #101018    outline / hair
+  s = #F2C09A    skin
+  b = #2E5FB7    shirt
+  d = #22406E    pants
+grid:
+  ..kkk...
+  ..kss...
+  ..kss...
+  .kbbbk..
+  ..bbb...
+  ..ddd...
+  .d...d..
+  .k...k..

pixel-sprite-maker/examples/walk_3.sprite

@@ -0,0 +1,16 @@
+# Frame 3/4 - legs together again (same pose as 1, arms swung).
+sprite: walk_3
+palette:
+  k = #101018    outline / hair
+  s = #F2C09A    skin
+  b = #2E5FB7    shirt
+  d = #22406E    pants
+grid:
+  ..kkk...
+  ..kss...
+  ..kss...
+  ..bbbk..
+  .kbbb...
+  ..ddd...
+  ..d.d...
+  ..k.k...

pixel-sprite-maker/examples/walk_4.sprite

@@ -0,0 +1,16 @@
+# Frame 4/4 - left leg forward.
+sprite: walk_4
+palette:
+  k = #101018    outline / hair
+  s = #F2C09A    skin
+  b = #2E5FB7    shirt
+  d = #22406E    pants
+grid:
+  ..kkk...
+  ..kss...
+  ..kss...
+  .kbbbk..
+  ..bbb...
+  ..ddd...
+  ..dd....
+  .k..k...

pixel-sprite-maker/go.mod

@@ -0,0 +1,3 @@
+module gitea.brasse-pc.eu/brasse/agent-tools/pixel-sprite-maker
+
+go 1.24

pixel-sprite-maker/main.go

@@ -0,0 +1,313 @@
+// spritec turns agent-friendly .sprite text files into PNG/JPG/SVG pixel
+// art, and combines several sprites into sprite sheets / animation strips.
+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"gitea.brasse-pc.eu/brasse/agent-tools/pixel-sprite-maker/sprite"
+)
+
+var version = "dev"
+
+const usage = `spritec - pixel sprite maker for agents
+
+Usage:
+  spritec render <file.sprite> [flags]   render one sprite to png/jpg/svg
+  spritec sheet <a.sprite> <b.sprite> ... [flags]
+                                          combine sprites into one sheet image
+  spritec info <file.sprite>              validate a file and print its stats
+  spritec preview <file.sprite>           draw the sprite in the terminal
+  spritec version                         print version
+
+Render flags:
+  -o <path>        output file; its extension picks the format (.png .jpg .svg)
+  --format <f>     png | jpg | svg (default: from -o, else png)
+  --scale <n>      integer upscale factor, default 1
+  --bg <color>     jpg background color (jpg has no alpha), default #FFFFFF
+  --quality <n>    jpg quality 1-100, default 90
+
+Sheet flags (in addition to the render flags):
+  -o <name>        output base name; layout is appended automatically
+  --cols <n>       number of columns, row-major order (default: one row)
+
+Sheet output naming:
+  <name>_<cellW>x<cellH>_<cols>x<rows>.<ext>
+  e.g. walk_16x16_4x2.png = 16x16 px per frame, 4 columns, 2 rows,
+  frames are read left-to-right then top-to-bottom (row-major).
+
+The .sprite format:
+  # comment
+  sprite: coin           optional name
+  palette:
+    . = none             '.' is transparent by default
+    k = #000000          hex, rgb(...), CSS names ('gold') and 'none' work
+    y = gold             anything after the color is a comment
+  grid:
+    ..kk..
+    .kyyk.
+    .kyyk.
+    ..kk..
+
+Each grid character is one pixel; every row must be the same width.
+Max sprite size: 256x256. Sheets may be bigger, single frames may not.
+`
+
+func main() {
+	if len(os.Args) < 2 {
+		fmt.Print(usage)
+		os.Exit(2)
+	}
+	switch os.Args[1] {
+	case "render":
+		cmdRender(os.Args[2:])
+	case "sheet":
+		cmdSheet(os.Args[2:])
+	case "info":
+		cmdInfo(os.Args[2:])
+	case "preview":
+		cmdPreview(os.Args[2:])
+	case "version", "--version", "-v":
+		fmt.Println("spritec", version)
+	case "help", "--help", "-h":
+		fmt.Print(usage)
+	default:
+		die("unknown command %q — run 'spritec help'", os.Args[1])
+	}
+}
+
+// parseInterspersed lets flags appear before or after positional args
+// (stdlib flag stops at the first positional otherwise).
+func parseInterspersed(fs *flag.FlagSet, args []string) {
+	var flags, pos []string
+	for i := 0; i < len(args); i++ {
+		a := args[i]
+		if len(a) > 1 && a[0] == '-' {
+			flags = append(flags, a)
+			name := strings.TrimLeft(a, "-")
+			if !strings.Contains(name, "=") {
+				f := fs.Lookup(name)
+				isBool := false
+				if f != nil {
+					if bv, ok := f.Value.(interface{ IsBoolFlag() bool }); ok && bv.IsBoolFlag() {
+						isBool = true
+					}
+				}
+				if !isBool && i+1 < len(args) {
+					i++
+					flags = append(flags, args[i])
+				}
+			}
+		} else {
+			pos = append(pos, a)
+		}
+	}
+	fs.Parse(append(flags, pos...))
+}
+
+type renderFlags struct {
+	out     string
+	format  string
+	scale   int
+	bg      string
+	quality int
+}
+
+func addRenderFlags(fs *flag.FlagSet) *renderFlags {
+	rf := &renderFlags{}
+	fs.StringVar(&rf.out, "o", "", "output path")
+	fs.StringVar(&rf.format, "format", "", "png|jpg|svg")
+	fs.IntVar(&rf.scale, "scale", 1, "integer upscale factor")
+	fs.StringVar(&rf.bg, "bg", "#FFFFFF", "jpg background color")
+	fs.IntVar(&rf.quality, "quality", 90, "jpg quality 1-100")
+	return rf
+}
+
+// resolveFormat picks the output format from --format or the -o extension.
+func (rf *renderFlags) resolveFormat() (string, error) {
+	ext := strings.ToLower(strings.TrimPrefix(filepath.Ext(rf.out), "."))
+	if ext == "jpeg" {
+		ext = "jpg"
+	}
+	f := strings.ToLower(rf.format)
+	switch {
+	case f == "" && ext == "":
+		return "png", nil
+	case f == "":
+		f = ext
+	case ext != "" && ext != f:
+		return "", fmt.Errorf("--format %s conflicts with output extension .%s", f, ext)
+	}
+	switch f {
+	case "png", "jpg", "svg":
+		return f, nil
+	}
+	return "", fmt.Errorf("unsupported format %q (png, jpg or svg)", f)
+}
+
+func writeGrid(path, format string, g sprite.PixelGrid, rf *renderFlags) error {
+	bg, err := sprite.ParseColor(rf.bg)
+	if err != nil {
+		return fmt.Errorf("--bg: %w", err)
+	}
+	f, err := os.Create(path)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+	switch format {
+	case "png":
+		err = sprite.WritePNG(f, g, rf.scale)
+	case "jpg":
+		err = sprite.WriteJPG(f, g, rf.scale, bg, rf.quality)
+	case "svg":
+		err = sprite.WriteSVG(f, g, rf.scale)
+	}
+	if err != nil {
+		return err
+	}
+	return f.Close()
+}
+
+func cmdRender(args []string) {
+	fs := flag.NewFlagSet("render", flag.ExitOnError)
+	rf := addRenderFlags(fs)
+	parseInterspersed(fs, args)
+	if fs.NArg() != 1 {
+		die("render takes exactly one .sprite file")
+	}
+	in := fs.Arg(0)
+	s, err := sprite.ParseFile(in)
+	if err != nil {
+		die("%v", err)
+	}
+	format, err := rf.resolveFormat()
+	if err != nil {
+		die("%v", err)
+	}
+	out := rf.out
+	if out == "" {
+		out = strings.TrimSuffix(in, filepath.Ext(in)) + "." + format
+	}
+	if err := writeGrid(out, format, s, rf); err != nil {
+		die("%v", err)
+	}
+	w, h := s.Bounds()
+	fmt.Printf("%s  (%dx%d px, scale %d -> %dx%d)\n", out, w, h, rf.scale, w*rf.scale, h*rf.scale)
+}
+
+func cmdSheet(args []string) {
+	fs := flag.NewFlagSet("sheet", flag.ExitOnError)
+	rf := addRenderFlags(fs)
+	cols := fs.Int("cols", 0, "columns in the sheet (default: all sprites in one row)")
+	parseInterspersed(fs, args)
+	if fs.NArg() < 1 {
+		die("sheet needs at least one .sprite file")
+	}
+	var sprites []*sprite.Sprite
+	for _, path := range fs.Args() {
+		s, err := sprite.ParseFile(path)
+		if err != nil {
+			die("%v", err)
+		}
+		sprites = append(sprites, s)
+	}
+	sh, err := sprite.NewSheet(sprites, *cols)
+	if err != nil {
+		die("%v", err)
+	}
+	format, err := rf.resolveFormat()
+	if err != nil {
+		die("%v", err)
+	}
+	base := rf.out
+	if base == "" {
+		base = "sheet"
+	}
+	base = strings.TrimSuffix(base, filepath.Ext(base))
+	out := sh.FileBase(base) + "." + format
+	if err := writeGrid(out, format, sh, rf); err != nil {
+		die("%v", err)
+	}
+	w, h := sh.Bounds()
+	fmt.Printf("%s  (%d frames of %dx%d px in %dx%d grid, total %dx%d px)\n",
+		out, len(sprites), sh.CellW, sh.CellH, sh.Cols, sh.Rows, w*rf.scale, h*rf.scale)
+}
+
+func cmdInfo(args []string) {
+	if len(args) != 1 {
+		die("info takes exactly one .sprite file")
+	}
+	s, err := sprite.ParseFile(args[0])
+	if err != nil {
+		die("%v", err)
+	}
+	fmt.Printf("sprite:  %s\n", s.Name)
+	fmt.Printf("size:    %dx%d px\n", s.W, s.H)
+	fmt.Printf("palette: %d colors\n", len(s.Keys))
+	usage := s.UsageCount()
+	for _, k := range s.Keys {
+		note := ""
+		if usage[k] == 0 {
+			note = "   (unused)"
+		}
+		fmt.Printf("  %s = %-9s  %5d px%s\n", string(k), sprite.FormatColor(s.Palette[k]), usage[k], note)
+	}
+	if _, defined := usage['.']; defined && !contains(s.Keys, '.') {
+		fmt.Printf("  . = none       %5d px   (implicit transparent)\n", usage['.'])
+	}
+	fmt.Println("valid:   yes")
+}
+
+func contains(keys []rune, k rune) bool {
+	for _, x := range keys {
+		if x == k {
+			return true
+		}
+	}
+	return false
+}
+
+// cmdPreview draws the sprite with truecolor half-blocks, two pixel rows
+// per terminal line. Transparent pixels show the terminal background.
+func cmdPreview(args []string) {
+	if len(args) != 1 {
+		die("preview takes exactly one .sprite file")
+	}
+	s, err := sprite.ParseFile(args[0])
+	if err != nil {
+		die("%v", err)
+	}
+	const reset = "\x1b[0m"
+	var b strings.Builder
+	for y := 0; y < s.H; y += 2 {
+		for x := 0; x < s.W; x++ {
+			top, bot := s.At(x, y), sprite.Transparent
+			if y+1 < s.H {
+				bot = s.At(x, y+1)
+			}
+			topOn, botOn := top.A >= 128, bot.A >= 128
+			switch {
+			case topOn && botOn:
+				fmt.Fprintf(&b, "\x1b[38;2;%d;%d;%dm\x1b[48;2;%d;%d;%dm▀%s", top.R, top.G, top.B, bot.R, bot.G, bot.B, reset)
+			case topOn:
+				fmt.Fprintf(&b, "\x1b[38;2;%d;%d;%dm▀%s", top.R, top.G, top.B, reset)
+			case botOn:
+				fmt.Fprintf(&b, "\x1b[38;2;%d;%d;%dm▄%s", bot.R, bot.G, bot.B, reset)
+			default:
+				b.WriteByte(' ')
+			}
+		}
+		b.WriteByte('\n')
+	}
+	fmt.Printf("%s  %dx%d px\n%s", s.Name, s.W, s.H, b.String())
+}
+
+func die(format string, a ...any) {
+	fmt.Fprintf(os.Stderr, "spritec: "+format+"\n", a...)
+	os.Exit(1)
+}

pixel-sprite-maker/sprite/color.go

@@ -0,0 +1,270 @@
+package sprite
+
+import (
+	"fmt"
+	"image/color"
+	"strconv"
+	"strings"
+)
+
+// Transparent is the color used for pixels that should not be drawn.
+var Transparent = color.NRGBA{0, 0, 0, 0}
+
+// ParseColor accepts:
+//
+//	none | transparent | -           -> fully transparent
+//	#RGB #RGBA #RRGGBB #RRGGBBAA     -> hex
+//	rgb(r,g,b) rgba(r,g,b,a)         -> 0-255 channels, alpha 0-255 or 0.0-1.0
+//	CSS named colors                 -> "red", "rebeccapurple", ...
+func ParseColor(s string) (color.NRGBA, error) {
+	t := strings.ToLower(strings.TrimSpace(s))
+	if t == "" {
+		return Transparent, fmt.Errorf("empty color value")
+	}
+	switch t {
+	case "none", "transparent", "-":
+		return Transparent, nil
+	}
+	if strings.HasPrefix(t, "#") {
+		return parseHex(t)
+	}
+	if strings.HasPrefix(t, "rgb(") || strings.HasPrefix(t, "rgba(") {
+		return parseRGBFunc(t)
+	}
+	if c, ok := cssColors[t]; ok {
+		return c, nil
+	}
+	return Transparent, fmt.Errorf("unknown color %q (use #RRGGBB, rgb(r,g,b), a CSS color name, or 'none')", s)
+}
+
+func parseHex(t string) (color.NRGBA, error) {
+	h := t[1:]
+	var r, g, b, a uint64
+	var err error
+	dup := func(s string) (uint64, error) {
+		v, err := strconv.ParseUint(s, 16, 8)
+		return v*16 + v, err
+	}
+	a = 255
+	switch len(h) {
+	case 3, 4:
+		if r, err = dup(h[0:1]); err == nil {
+			if g, err = dup(h[1:2]); err == nil {
+				b, err = dup(h[2:3])
+			}
+		}
+		if err == nil && len(h) == 4 {
+			a, err = dup(h[3:4])
+		}
+	case 6, 8:
+		if r, err = strconv.ParseUint(h[0:2], 16, 8); err == nil {
+			if g, err = strconv.ParseUint(h[2:4], 16, 8); err == nil {
+				b, err = strconv.ParseUint(h[4:6], 16, 8)
+			}
+		}
+		if err == nil && len(h) == 8 {
+			a, err = strconv.ParseUint(h[6:8], 16, 8)
+		}
+	default:
+		return Transparent, fmt.Errorf("hex color %q must be #RGB, #RGBA, #RRGGBB or #RRGGBBAA", t)
+	}
+	if err != nil {
+		return Transparent, fmt.Errorf("invalid hex color %q", t)
+	}
+	return color.NRGBA{uint8(r), uint8(g), uint8(b), uint8(a)}, nil
+}
+
+func parseRGBFunc(t string) (color.NRGBA, error) {
+	open := strings.Index(t, "(")
+	close := strings.Index(t, ")")
+	if close < open {
+		return Transparent, fmt.Errorf("invalid color %q: missing ')'", t)
+	}
+	parts := strings.Split(t[open+1:close], ",")
+	if len(parts) != 3 && len(parts) != 4 {
+		return Transparent, fmt.Errorf("invalid color %q: want rgb(r,g,b) or rgba(r,g,b,a)", t)
+	}
+	var ch [4]uint8
+	ch[3] = 255
+	for i, p := range parts {
+		p = strings.TrimSpace(p)
+		if i == 3 && strings.Contains(p, ".") {
+			// CSS-style fractional alpha 0.0 - 1.0
+			f, err := strconv.ParseFloat(p, 64)
+			if err != nil || f < 0 || f > 1 {
+				return Transparent, fmt.Errorf("invalid alpha %q in %q (want 0.0-1.0 or 0-255)", p, t)
+			}
+			ch[3] = uint8(f*255 + 0.5)
+			continue
+		}
+		v, err := strconv.ParseUint(p, 10, 8)
+		if err != nil {
+			return Transparent, fmt.Errorf("invalid channel %q in %q (want 0-255)", p, t)
+		}
+		ch[i] = uint8(v)
+	}
+	return color.NRGBA{ch[0], ch[1], ch[2], ch[3]}, nil
+}
+
+// FormatColor renders a color the way it should appear in a .sprite file.
+func FormatColor(c color.NRGBA) string {
+	if c.A == 0 {
+		return "none"
+	}
+	if c.A == 255 {
+		return fmt.Sprintf("#%02X%02X%02X", c.R, c.G, c.B)
+	}
+	return fmt.Sprintf("#%02X%02X%02X%02X", c.R, c.G, c.B, c.A)
+}
+
+// cssColors is the full CSS Color Module Level 4 named-color list.
+var cssColors = map[string]color.NRGBA{
+	"aliceblue":            {240, 248, 255, 255},
+	"antiquewhite":         {250, 235, 215, 255},
+	"aqua":                 {0, 255, 255, 255},
+	"aquamarine":           {127, 255, 212, 255},
+	"azure":                {240, 255, 255, 255},
+	"beige":                {245, 245, 220, 255},
+	"bisque":               {255, 228, 196, 255},
+	"black":                {0, 0, 0, 255},
+	"blanchedalmond":       {255, 235, 205, 255},
+	"blue":                 {0, 0, 255, 255},
+	"blueviolet":           {138, 43, 226, 255},
+	"brown":                {165, 42, 42, 255},
+	"burlywood":            {222, 184, 135, 255},
+	"cadetblue":            {95, 158, 160, 255},
+	"chartreuse":           {127, 255, 0, 255},
+	"chocolate":            {210, 105, 30, 255},
+	"coral":                {255, 127, 80, 255},
+	"cornflowerblue":       {100, 149, 237, 255},
+	"cornsilk":             {255, 248, 220, 255},
+	"crimson":              {220, 20, 60, 255},
+	"cyan":                 {0, 255, 255, 255},
+	"darkblue":             {0, 0, 139, 255},
+	"darkcyan":             {0, 139, 139, 255},
+	"darkgoldenrod":        {184, 134, 11, 255},
+	"darkgray":             {169, 169, 169, 255},
+	"darkgreen":            {0, 100, 0, 255},
+	"darkgrey":             {169, 169, 169, 255},
+	"darkkhaki":            {189, 183, 107, 255},
+	"darkmagenta":          {139, 0, 139, 255},
+	"darkolivegreen":       {85, 107, 47, 255},
+	"darkorange":           {255, 140, 0, 255},
+	"darkorchid":           {153, 50, 204, 255},
+	"darkred":              {139, 0, 0, 255},
+	"darksalmon":           {233, 150, 122, 255},
+	"darkseagreen":         {143, 188, 143, 255},
+	"darkslateblue":        {72, 61, 139, 255},
+	"darkslategray":        {47, 79, 79, 255},
+	"darkslategrey":        {47, 79, 79, 255},
+	"darkturquoise":        {0, 206, 209, 255},
+	"darkviolet":           {148, 0, 211, 255},
+	"deeppink":             {255, 20, 147, 255},
+	"deepskyblue":          {0, 191, 255, 255},
+	"dimgray":              {105, 105, 105, 255},
+	"dimgrey":              {105, 105, 105, 255},
+	"dodgerblue":           {30, 144, 255, 255},
+	"firebrick":            {178, 34, 34, 255},
+	"floralwhite":          {255, 250, 240, 255},
+	"forestgreen":          {34, 139, 34, 255},
+	"fuchsia":              {255, 0, 255, 255},
+	"gainsboro":            {220, 220, 220, 255},
+	"ghostwhite":           {248, 248, 255, 255},
+	"gold":                 {255, 215, 0, 255},
+	"goldenrod":            {218, 165, 32, 255},
+	"gray":                 {128, 128, 128, 255},
+	"green":                {0, 128, 0, 255},
+	"greenyellow":          {173, 255, 47, 255},
+	"grey":                 {128, 128, 128, 255},
+	"honeydew":             {240, 255, 240, 255},
+	"hotpink":              {255, 105, 180, 255},
+	"indianred":            {205, 92, 92, 255},
+	"indigo":               {75, 0, 130, 255},
+	"ivory":                {255, 255, 240, 255},
+	"khaki":                {240, 230, 140, 255},
+	"lavender":             {230, 230, 250, 255},
+	"lavenderblush":        {255, 240, 245, 255},
+	"lawngreen":            {124, 252, 0, 255},
+	"lemonchiffon":         {255, 250, 205, 255},
+	"lightblue":            {173, 216, 230, 255},
+	"lightcoral":           {240, 128, 128, 255},
+	"lightcyan":            {224, 255, 255, 255},
+	"lightgoldenrodyellow": {250, 250, 210, 255},
+	"lightgray":            {211, 211, 211, 255},
+	"lightgreen":           {144, 238, 144, 255},
+	"lightgrey":            {211, 211, 211, 255},
+	"lightpink":            {255, 182, 193, 255},
+	"lightsalmon":          {255, 160, 122, 255},
+	"lightseagreen":        {32, 178, 170, 255},
+	"lightskyblue":         {135, 206, 250, 255},
+	"lightslategray":       {119, 136, 153, 255},
+	"lightslategrey":       {119, 136, 153, 255},
+	"lightsteelblue":       {176, 196, 222, 255},
+	"lightyellow":          {255, 255, 224, 255},
+	"lime":                 {0, 255, 0, 255},
+	"limegreen":            {50, 205, 50, 255},
+	"linen":                {250, 240, 230, 255},
+	"magenta":              {255, 0, 255, 255},
+	"maroon":               {128, 0, 0, 255},
+	"mediumaquamarine":     {102, 205, 170, 255},
+	"mediumblue":           {0, 0, 205, 255},
+	"mediumorchid":         {186, 85, 211, 255},
+	"mediumpurple":         {147, 112, 219, 255},
+	"mediumseagreen":       {60, 179, 113, 255},
+	"mediumslateblue":      {123, 104, 238, 255},
+	"mediumspringgreen":    {0, 250, 154, 255},
+	"mediumturquoise":      {72, 209, 204, 255},
+	"mediumvioletred":      {199, 21, 133, 255},
+	"midnightblue":         {25, 25, 112, 255},
+	"mintcream":            {245, 255, 250, 255},
+	"mistyrose":            {255, 228, 225, 255},
+	"moccasin":             {255, 228, 181, 255},
+	"navajowhite":          {255, 222, 173, 255},
+	"navy":                 {0, 0, 128, 255},
+	"oldlace":              {253, 245, 230, 255},
+	"olive":                {128, 128, 0, 255},
+	"olivedrab":            {107, 142, 35, 255},
+	"orange":               {255, 165, 0, 255},
+	"orangered":            {255, 69, 0, 255},
+	"orchid":               {218, 112, 214, 255},
+	"palegoldenrod":        {238, 232, 170, 255},
+	"palegreen":            {152, 251, 152, 255},
+	"paleturquoise":        {175, 238, 238, 255},
+	"palevioletred":        {219, 112, 147, 255},
+	"papayawhip":           {255, 239, 213, 255},
+	"peachpuff":            {255, 218, 185, 255},
+	"peru":                 {205, 133, 63, 255},
+	"pink":                 {255, 192, 203, 255},
+	"plum":                 {221, 160, 221, 255},
+	"powderblue":           {176, 224, 230, 255},
+	"purple":               {128, 0, 128, 255},
+	"rebeccapurple":        {102, 51, 153, 255},
+	"red":                  {255, 0, 0, 255},
+	"rosybrown":            {188, 143, 143, 255},
+	"royalblue":            {65, 105, 225, 255},
+	"saddlebrown":          {139, 69, 19, 255},
+	"salmon":               {250, 128, 114, 255},
+	"sandybrown":           {244, 164, 96, 255},
+	"seagreen":             {46, 139, 87, 255},
+	"seashell":             {255, 245, 238, 255},
+	"sienna":               {160, 82, 45, 255},
+	"silver":               {192, 192, 192, 255},
+	"skyblue":              {135, 206, 235, 255},
+	"slateblue":            {106, 90, 205, 255},
+	"slategray":            {112, 128, 144, 255},
+	"slategrey":            {112, 128, 144, 255},
+	"snow":                 {255, 250, 250, 255},
+	"springgreen":          {0, 255, 127, 255},
+	"steelblue":            {70, 130, 180, 255},
+	"tan":                  {210, 180, 140, 255},
+	"teal":                 {0, 128, 128, 255},
+	"thistle":              {216, 191, 216, 255},
+	"tomato":               {255, 99, 71, 255},
+	"turquoise":            {64, 224, 208, 255},
+	"violet":               {238, 130, 238, 255},
+	"wheat":                {245, 222, 179, 255},
+	"white":                {255, 255, 255, 255},
+	"whitesmoke":           {245, 245, 245, 255},
+	"yellow":               {255, 255, 0, 255},
+	"yellowgreen":          {154, 205, 50, 255},
+}

pixel-sprite-maker/sprite/parse.go

@@ -0,0 +1,186 @@
+package sprite
+
+import (
+	"bufio"
+	"fmt"
+	"image/color"
+	"io"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+// MaxSize is the maximum width/height of a single sprite in pixels.
+const MaxSize = 256
+
+// Sprite is a parsed .sprite file: a palette of single-rune keys and a
+// rectangular grid of those keys.
+type Sprite struct {
+	Name    string
+	W, H    int
+	Palette map[rune]color.NRGBA
+	Keys    []rune   // palette keys in file order
+	Rows    [][]rune // H rows of exactly W palette keys
+}
+
+// At returns the color of pixel (x, y). Out-of-range pixels are transparent.
+func (s *Sprite) At(x, y int) color.NRGBA {
+	if x < 0 || y < 0 || x >= s.W || y >= s.H {
+		return Transparent
+	}
+	return s.Palette[s.Rows[y][x]]
+}
+
+// Bounds returns the sprite size in pixels.
+func (s *Sprite) Bounds() (w, h int) { return s.W, s.H }
+
+// ParseFile reads a .sprite file from disk. The sprite name defaults to the
+// file name without extension when the file has no "sprite:" line.
+func ParseFile(path string) (*Sprite, error) {
+	f, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+	s, err := Parse(f)
+	if err != nil {
+		return nil, fmt.Errorf("%s: %w", path, err)
+	}
+	if s.Name == "" {
+		s.Name = strings.TrimSuffix(filepath.Base(path), filepath.Ext(path))
+	}
+	return s, nil
+}
+
+// Parse reads the .sprite text format:
+//
+//	# comment lines start with '#'
+//	sprite: coin              (optional name)
+//	palette:
+//	  . = none                (key '.' is transparent by default)
+//	  k = #000000             text after the color is ignored
+//	  y = gold
+//	grid:
+//	  ..kk..
+//	  .kyyk.
+//
+// Palette keys are exactly one character and may not be '#', '=', ':' or
+// whitespace. Every grid row must be the same width; max size is 256x256.
+func Parse(r io.Reader) (*Sprite, error) {
+	s := &Sprite{Palette: map[rune]color.NRGBA{}}
+	const (
+		secNone = iota
+		secPalette
+		secGrid
+	)
+	section := secNone
+	sc := bufio.NewScanner(r)
+	sc.Buffer(make([]byte, 0, 64*1024), 1024*1024)
+	lineNo := 0
+	for sc.Scan() {
+		lineNo++
+		line := strings.TrimSpace(sc.Text())
+		if line == "" || strings.HasPrefix(line, "#") {
+			continue // comment or blank ('#' is not a legal palette key)
+		}
+		lower := strings.ToLower(line)
+		switch {
+		case lower == "palette:":
+			section = secPalette
+			continue
+		case lower == "grid:":
+			section = secGrid
+			continue
+		case strings.HasPrefix(lower, "sprite:"):
+			s.Name = strings.TrimSpace(line[len("sprite:"):])
+			continue
+		}
+		switch section {
+		case secPalette:
+			if err := s.parsePaletteLine(line, lineNo); err != nil {
+				return nil, err
+			}
+		case secGrid:
+			row := []rune(line)
+			s.Rows = append(s.Rows, row)
+		default:
+			return nil, fmt.Errorf("line %d: unexpected %q before a 'palette:' or 'grid:' section", lineNo, line)
+		}
+	}
+	if err := sc.Err(); err != nil {
+		return nil, err
+	}
+	return s, s.validate()
+}
+
+func (s *Sprite) parsePaletteLine(line string, lineNo int) error {
+	eq := strings.Index(line, "=")
+	if eq < 0 {
+		return fmt.Errorf("line %d: palette entry %q must look like '<key> = <color>'", lineNo, line)
+	}
+	keyPart := []rune(strings.TrimSpace(line[:eq]))
+	if len(keyPart) != 1 {
+		return fmt.Errorf("line %d: palette key %q must be exactly one character", lineNo, strings.TrimSpace(line[:eq]))
+	}
+	key := keyPart[0]
+	if key == '#' || key == '=' || key == ':' {
+		return fmt.Errorf("line %d: %q is not allowed as a palette key", lineNo, key)
+	}
+	if _, dup := s.Palette[key]; dup {
+		return fmt.Errorf("line %d: palette key %q defined twice", lineNo, key)
+	}
+	val := strings.TrimSpace(line[eq+1:])
+	// The color is the first token; anything after it is a free-text comment.
+	token := val
+	if strings.HasPrefix(strings.ToLower(val), "rgb") {
+		if close := strings.Index(val, ")"); close >= 0 {
+			token = val[:close+1]
+		}
+	} else if i := strings.IndexAny(val, " \t"); i >= 0 {
+		token = val[:i]
+	}
+	c, err := ParseColor(token)
+	if err != nil {
+		return fmt.Errorf("line %d: %w", lineNo, err)
+	}
+	s.Palette[key] = c
+	s.Keys = append(s.Keys, key)
+	return nil
+}
+
+func (s *Sprite) validate() error {
+	if len(s.Rows) == 0 {
+		return fmt.Errorf("no 'grid:' section with at least one row found")
+	}
+	// '.' is transparent unless the file overrides it.
+	if _, ok := s.Palette['.']; !ok {
+		s.Palette['.'] = Transparent
+	}
+	s.H = len(s.Rows)
+	s.W = len(s.Rows[0])
+	if s.W > MaxSize || s.H > MaxSize {
+		return fmt.Errorf("sprite is %dx%d pixels; the maximum is %dx%d", s.W, s.H, MaxSize, MaxSize)
+	}
+	for y, row := range s.Rows {
+		if len(row) != s.W {
+			return fmt.Errorf("grid row %d is %d pixels wide, expected %d (all rows must match row 1)", y+1, len(row), s.W)
+		}
+		for x, key := range row {
+			if _, ok := s.Palette[key]; !ok {
+				return fmt.Errorf("grid row %d, column %d: %q is not defined in the palette", y+1, x+1, string(key))
+			}
+		}
+	}
+	return nil
+}
+
+// UsageCount returns how many grid pixels use each palette key.
+func (s *Sprite) UsageCount() map[rune]int {
+	n := map[rune]int{}
+	for _, row := range s.Rows {
+		for _, k := range row {
+			n[k]++
+		}
+	}
+	return n
+}

pixel-sprite-maker/sprite/render.go

@@ -0,0 +1,75 @@
+package sprite
+
+import (
+	"fmt"
+	"image"
+	"image/color"
+	"image/jpeg"
+	"image/png"
+	"io"
+)
+
+// PixelGrid is anything that can be rendered pixel by pixel: a single
+// Sprite or a composed Sheet.
+type PixelGrid interface {
+	Bounds() (w, h int)
+	At(x, y int) color.NRGBA
+}
+
+// Image renders a PixelGrid to an NRGBA image, scaled up by the integer
+// factor scale (nearest neighbour, keeps pixels crisp).
+func Image(g PixelGrid, scale int) *image.NRGBA {
+	if scale < 1 {
+		scale = 1
+	}
+	w, h := g.Bounds()
+	img := image.NewNRGBA(image.Rect(0, 0, w*scale, h*scale))
+	for y := 0; y < h; y++ {
+		for x := 0; x < w; x++ {
+			c := g.At(x, y)
+			for dy := 0; dy < scale; dy++ {
+				for dx := 0; dx < scale; dx++ {
+					img.SetNRGBA(x*scale+dx, y*scale+dy, c)
+				}
+			}
+		}
+	}
+	return img
+}
+
+// WritePNG encodes g as PNG with transparency preserved.
+func WritePNG(w io.Writer, g PixelGrid, scale int) error {
+	return png.Encode(w, Image(g, scale))
+}
+
+// WriteJPG encodes g as JPEG. JPEG has no alpha channel, so transparent
+// pixels are composited over bg first.
+func WriteJPG(w io.Writer, g PixelGrid, scale int, bg color.NRGBA, quality int) error {
+	if quality < 1 || quality > 100 {
+		return fmt.Errorf("jpg quality %d out of range 1-100", quality)
+	}
+	src := Image(g, scale)
+	b := src.Bounds()
+	flat := image.NewRGBA(b)
+	for y := b.Min.Y; y < b.Max.Y; y++ {
+		for x := b.Min.X; x < b.Max.X; x++ {
+			flat.Set(x, y, blendOver(src.NRGBAAt(x, y), bg))
+		}
+	}
+	return jpeg.Encode(w, flat, &jpeg.Options{Quality: quality})
+}
+
+// blendOver composites src over an opaque background color.
+func blendOver(src, bg color.NRGBA) color.NRGBA {
+	if src.A == 255 {
+		return src
+	}
+	a := uint32(src.A)
+	inv := 255 - a
+	return color.NRGBA{
+		R: uint8((uint32(src.R)*a + uint32(bg.R)*inv) / 255),
+		G: uint8((uint32(src.G)*a + uint32(bg.G)*inv) / 255),
+		B: uint8((uint32(src.B)*a + uint32(bg.B)*inv) / 255),
+		A: 255,
+	}
+}

pixel-sprite-maker/sprite/sheet.go

@@ -0,0 +1,58 @@
+package sprite
+
+import (
+	"fmt"
+	"image/color"
+)
+
+// Sheet lays out several equally sized sprites in a row-major grid:
+// index 0 is top-left, then left-to-right, then next row. A 1D strip is
+// simply a sheet with one row (or one column).
+type Sheet struct {
+	Sprites      []*Sprite
+	Cols, Rows   int
+	CellW, CellH int
+}
+
+// NewSheet composes sprites into a sheet with the given number of columns.
+// cols <= 0 puts everything in a single row. Every sprite must have the
+// same dimensions so the sheet can be indexed cell by cell.
+func NewSheet(sprites []*Sprite, cols int) (*Sheet, error) {
+	if len(sprites) == 0 {
+		return nil, fmt.Errorf("a sheet needs at least one sprite")
+	}
+	w, h := sprites[0].Bounds()
+	for _, sp := range sprites[1:] {
+		sw, sh := sp.Bounds()
+		if sw != w || sh != h {
+			return nil, fmt.Errorf("sprite %q is %dx%d but %q is %dx%d — all sprites in a sheet must be the same size",
+				sp.Name, sw, sh, sprites[0].Name, w, h)
+		}
+	}
+	if cols <= 0 || cols > len(sprites) {
+		cols = len(sprites)
+	}
+	rows := (len(sprites) + cols - 1) / cols
+	return &Sheet{Sprites: sprites, Cols: cols, Rows: rows, CellW: w, CellH: h}, nil
+}
+
+// Bounds returns the total sheet size in pixels.
+func (sh *Sheet) Bounds() (w, h int) { return sh.Cols * sh.CellW, sh.Rows * sh.CellH }
+
+// At returns the pixel at (x, y). Cells past the last sprite (when the
+// sprite count doesn't fill the grid) are transparent.
+func (sh *Sheet) At(x, y int) color.NRGBA {
+	col, row := x/sh.CellW, y/sh.CellH
+	idx := row*sh.Cols + col
+	if idx >= len(sh.Sprites) {
+		return Transparent
+	}
+	return sh.Sprites[idx].At(x%sh.CellW, y%sh.CellH)
+}
+
+// FileBase appends the layout to an output name so the file itself
+// documents cell size and orientation: <base>_<cellW>x<cellH>_<cols>x<rows>
+// e.g. walk_16x16_4x2 = 16x16 cells, 4 columns, 2 rows, read row by row.
+func (sh *Sheet) FileBase(base string) string {
+	return fmt.Sprintf("%s_%dx%d_%dx%d", base, sh.CellW, sh.CellH, sh.Cols, sh.Rows)
+}

pixel-sprite-maker/sprite/sprite_test.go

@@ -0,0 +1,207 @@
+package sprite
+
+import (
+	"bytes"
+	"encoding/xml"
+	"image/color"
+	"strings"
+	"testing"
+)
+
+const coin = `
+# a tiny coin
+sprite: coin
+palette:
+  k = #000000
+  y = gold
+  Y = #FFF3A0 highlight
+grid:
+  .kk.
+  kyYk
+  kyyk
+  .kk.
+`
+
+func parseOK(t *testing.T, src string) *Sprite {
+	t.Helper()
+	s, err := Parse(strings.NewReader(src))
+	if err != nil {
+		t.Fatalf("parse failed: %v", err)
+	}
+	return s
+}
+
+func TestParseBasics(t *testing.T) {
+	s := parseOK(t, coin)
+	if s.Name != "coin" {
+		t.Errorf("name = %q, want coin", s.Name)
+	}
+	if s.W != 4 || s.H != 4 {
+		t.Errorf("size = %dx%d, want 4x4", s.W, s.H)
+	}
+	if got := s.At(0, 0); got.A != 0 {
+		t.Errorf("(0,0) should be transparent via the implicit '.', got %v", got)
+	}
+	if got := s.At(1, 1); got != (color.NRGBA{255, 215, 0, 255}) {
+		t.Errorf("(1,1) = %v, want gold", got)
+	}
+	if got := s.At(2, 1); got != (color.NRGBA{255, 243, 160, 255}) {
+		t.Errorf("(2,1) = %v, want #FFF3A0", got)
+	}
+}
+
+func TestParseErrors(t *testing.T) {
+	cases := map[string]string{
+		"ragged rows":   "palette:\n a = red\ngrid:\naa\naaa\n",
+		"unknown key":   "palette:\n a = red\ngrid:\nab\naa\n",
+		"bad color":     "palette:\n a = notacolor\ngrid:\na\n",
+		"no grid":       "palette:\n a = red\n",
+		"dup key":       "palette:\n a = red\n a = blue\ngrid:\na\n",
+		"multirune key": "palette:\n ab = red\ngrid:\na\n",
+		"colon key":     "palette:\n : = red\ngrid:\n.\n",
+	}
+	for name, src := range cases {
+		if _, err := Parse(strings.NewReader(src)); err == nil {
+			t.Errorf("%s: expected an error", name)
+		}
+	}
+}
+
+func TestMaxSize(t *testing.T) {
+	row := strings.Repeat("a", 257)
+	src := "palette:\n a = red\ngrid:\n" + row + "\n"
+	if _, err := Parse(strings.NewReader(src)); err == nil {
+		t.Error("257 px wide sprite should be rejected")
+	}
+	ok := "palette:\n a = red\ngrid:\n" + strings.Repeat(strings.Repeat("a", 256)+"\n", 256)
+	s := parseOK(t, ok)
+	if s.W != 256 || s.H != 256 {
+		t.Errorf("size = %dx%d, want 256x256", s.W, s.H)
+	}
+}
+
+func TestParseColorForms(t *testing.T) {
+	cases := map[string]color.NRGBA{
+		"none":              {0, 0, 0, 0},
+		"-":                 {0, 0, 0, 0},
+		"#F00":              {255, 0, 0, 255},
+		"#F00A":             {255, 0, 0, 170},
+		"#00FF00":           {0, 255, 0, 255},
+		"#00FF0080":         {0, 255, 0, 128},
+		"rgb(1,2,3)":        {1, 2, 3, 255},
+		"rgba(1,2,3,64)":    {1, 2, 3, 64},
+		"rgba(1, 2, 3, .5)": {1, 2, 3, 128},
+		"RebeccaPurple":     {102, 51, 153, 255},
+	}
+	for in, want := range cases {
+		got, err := ParseColor(in)
+		if err != nil {
+			t.Errorf("ParseColor(%q): %v", in, err)
+			continue
+		}
+		if got != want {
+			t.Errorf("ParseColor(%q) = %v, want %v", in, got, want)
+		}
+	}
+	for _, bad := range []string{"", "#12345", "rgb(300,0,0)", "purpleish"} {
+		if _, err := ParseColor(bad); err == nil {
+			t.Errorf("ParseColor(%q): expected error", bad)
+		}
+	}
+}
+
+func TestImageAndScale(t *testing.T) {
+	s := parseOK(t, coin)
+	img := Image(s, 3)
+	if b := img.Bounds(); b.Dx() != 12 || b.Dy() != 12 {
+		t.Fatalf("scaled bounds = %v, want 12x12", b)
+	}
+	// pixel (1,1) is gold -> block at (3..5, 3..5)
+	if got := img.NRGBAAt(4, 4); got != (color.NRGBA{255, 215, 0, 255}) {
+		t.Errorf("scaled gold pixel = %v", got)
+	}
+	if got := img.NRGBAAt(0, 0); got.A != 0 {
+		t.Errorf("corner should stay transparent, got %v", got)
+	}
+}
+
+func TestSVGOutput(t *testing.T) {
+	s := parseOK(t, coin)
+	var buf bytes.Buffer
+	if err := WriteSVG(&buf, s, 10); err != nil {
+		t.Fatal(err)
+	}
+	out := buf.String()
+	if !strings.Contains(out, `viewBox="0 0 4 4"`) || !strings.Contains(out, `width="40"`) {
+		t.Errorf("svg header wrong:\n%s", out)
+	}
+	// row 2 (y=1) has runs k, yY?, no: k y Y k -> y and Y differ, so no merge.
+	// row 3 (y=2) k yy k -> the two golds merge into one rect of width 2.
+	if !strings.Contains(out, `<rect x="1" y="2" width="2" height="1" fill="#ffd700"/>`) {
+		t.Errorf("expected RLE-merged gold rect:\n%s", out)
+	}
+	var doc struct{ XMLName xml.Name }
+	if err := xml.Unmarshal(buf.Bytes(), &doc); err != nil {
+		t.Errorf("svg is not valid XML: %v", err)
+	}
+}
+
+func TestSheetLayoutAndNaming(t *testing.T) {
+	a := parseOK(t, coin)
+	b := parseOK(t, coin)
+	c := parseOK(t, coin)
+	sh, err := NewSheet([]*Sprite{a, b, c}, 2)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if sh.Cols != 2 || sh.Rows != 2 {
+		t.Errorf("layout = %dx%d, want 2x2", sh.Cols, sh.Rows)
+	}
+	if w, h := sh.Bounds(); w != 8 || h != 8 {
+		t.Errorf("bounds = %dx%d, want 8x8", w, h)
+	}
+	if got := sh.FileBase("walk"); got != "walk_4x4_2x2" {
+		t.Errorf("FileBase = %q, want walk_4x4_2x2", got)
+	}
+	// cell (1,1) in frame 2 (top-right) is gold
+	if got := sh.At(5, 1); got != (color.NRGBA{255, 215, 0, 255}) {
+		t.Errorf("sheet pixel in frame 2 = %v, want gold", got)
+	}
+	// 4th cell (bottom-right) has no sprite -> transparent
+	if got := sh.At(7, 7); got.A != 0 {
+		t.Errorf("empty cell should be transparent, got %v", got)
+	}
+}
+
+func TestSheetSizeMismatch(t *testing.T) {
+	a := parseOK(t, coin)
+	b := parseOK(t, "palette:\n a = red\ngrid:\naa\n")
+	if _, err := NewSheet([]*Sprite{a, b}, 0); err == nil {
+		t.Error("mismatched sprite sizes should be rejected")
+	}
+}
+
+func TestSheetDefaultSingleRow(t *testing.T) {
+	a := parseOK(t, coin)
+	sh, err := NewSheet([]*Sprite{a, a, a}, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if sh.Cols != 3 || sh.Rows != 1 {
+		t.Errorf("default layout = %dx%d, want 3x1", sh.Cols, sh.Rows)
+	}
+}
+
+func TestJPGComposite(t *testing.T) {
+	s := parseOK(t, coin)
+	var buf bytes.Buffer
+	if err := WriteJPG(&buf, s, 1, color.NRGBA{255, 255, 255, 255}, 90); err != nil {
+		t.Fatal(err)
+	}
+	if buf.Len() == 0 {
+		t.Error("empty jpg output")
+	}
+	if err := WriteJPG(&buf, s, 1, Transparent, 150); err == nil {
+		t.Error("quality 150 should be rejected")
+	}
+}

pixel-sprite-maker/sprite/svg.go

@@ -0,0 +1,46 @@
+package sprite
+
+import (
+	"fmt"
+	"io"
+)
+
+// WriteSVG encodes g as an SVG where each horizontal run of same-colored
+// pixels becomes one <rect>. shape-rendering="crispEdges" keeps the pixel
+// look at any zoom. scale only affects the document width/height; the
+// viewBox stays in pixel units.
+func WriteSVG(w io.Writer, g PixelGrid, scale int) error {
+	if scale < 1 {
+		scale = 1
+	}
+	gw, gh := g.Bounds()
+	_, err := fmt.Fprintf(w,
+		`<svg xmlns="http://www.w3.org/2000/svg" width="%d" height="%d" viewBox="0 0 %d %d" shape-rendering="crispEdges">`+"\n",
+		gw*scale, gh*scale, gw, gh)
+	if err != nil {
+		return err
+	}
+	for y := 0; y < gh; y++ {
+		for x := 0; x < gw; {
+			c := g.At(x, y)
+			run := 1
+			for x+run < gw && g.At(x+run, y) == c {
+				run++
+			}
+			if c.A > 0 {
+				opacity := ""
+				if c.A < 255 {
+					opacity = fmt.Sprintf(` fill-opacity="%.3f"`, float64(c.A)/255)
+				}
+				_, err = fmt.Fprintf(w, `<rect x="%d" y="%d" width="%d" height="1" fill="#%02x%02x%02x"%s/>`+"\n",
+					x, y, run, c.R, c.G, c.B, opacity)
+				if err != nil {
+					return err
+				}
+			}
+			x += run
+		}
+	}
+	_, err = io.WriteString(w, "</svg>\n")
+	return err
+}