bitmap-font-maker: fontc - .font glyph grids -> atlas PNG + metrics JSON + text rendering

- .font format: glyph sections with #/. grids, proportional widths,
  literal unicode glyph names, spacing/space-width/line-height/baseline
- build (atlas white-on-transparent + JSON metrics), render (text -> PNG
  with \n, scale, color), info, preview (terminal half-blocks)
- example tiny5 font: A-Z, ÅÄÖ, 0-9, punctuation (47 glyphs, 3x5)
- go tests: parsing, errors, atlas metrics, text rendering

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MmdG9GqfSWCzts7AkDwRDh
This commit is contained in:
2026-07-14 07:03:04 +02:00
parent a5b8a249ed
commit 6b10c4a57c
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# bitmap-font-maker (`fontc`)
Turns `.font` text files — pixel glyph grids an agent can read and edit
directly — into **font atlases (PNG + JSON metrics)** and renders text
strings to PNG. Proportional widths, unicode glyph names (ÅÄÖ works).
Go, zero dependencies, single static binary.
## Build
```bash
# Arch/Garuda: sudo pacman -S go
cd bitmap-font-maker
go build -o build/fontc . # or the VS Code task "build bitmap-font-maker"
go test ./...
```
## The `.font` format
```
# comment
font: tiny5 optional name
spacing: 1 px between glyphs (default 1)
space-width: 3 advance of ' ' (default: width of '0')
line-height: 7 default: glyph height + 1
baseline: 5 default: glyph height
glyph A:
.#.
#.#
###
#.#
#.#
glyph :: the char between "glyph " and ":" is literal
.
#
.
#
.
```
- `#` = pixel on, `.` = off.
- **All glyphs share one height; widths may differ** (proportional fonts —
`M` can be 5 px wide while `.` is 1 px).
- Max glyph size 64x64.
## Commands
```bash
fontc build tiny5.font -o out/tiny5 # -> tiny5.png (atlas) + tiny5.json (metrics)
fontc render tiny5.font 'HEJ!\nRAD 2' --scale 4 --color '#FFD700' -o title.png
fontc info tiny5.font # validate + list glyphs
fontc preview tiny5.font 'HELLO' # draw in the terminal
```
## Atlas + metrics
The atlas draws glyphs **white on transparent** so game engines can tint
them. The JSON carries everything a loader needs:
```json
{
"name": "tiny5", "atlas": "tiny5.png",
"height": 5, "lineHeight": 6, "baseline": 5,
"spacing": 1, "spaceWidth": 3,
"glyphs": { "A": {"x": 0, "y": 0, "w": 3, "h": 5, "advance": 4}, ... }
}
```
Drawing text in a game: blit `glyphs[c]` from the atlas, advance the
cursor by `advance`; spaces advance `spaceWidth + spacing`; new lines
step `lineHeight`.
[`examples/tiny5.font`](examples/tiny5.font) is a complete 3x5 font:
A-Z, ÅÄÖ, 0-9 and punctuation.

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{
"name": "tiny5",
"atlas": "tiny5.png",
"height": 5,
"lineHeight": 6,
"baseline": 5,
"spacing": 1,
"spaceWidth": 3,
"glyphs": {
"!": {
"x": 36,
"y": 30,
"w": 1,
"h": 5,
"advance": 2
},
"'": {
"x": 24,
"y": 36,
"w": 1,
"h": 5,
"advance": 2
},
"+": {
"x": 18,
"y": 36,
"w": 3,
"h": 5,
"advance": 4
},
",": {
"x": 30,
"y": 30,
"w": 2,
"h": 5,
"advance": 3
},
"-": {
"x": 12,
"y": 36,
"w": 3,
"h": 5,
"advance": 4
},
".": {
"x": 24,
"y": 30,
"w": 1,
"h": 5,
"advance": 2
},
"0": {
"x": 6,
"y": 24,
"w": 3,
"h": 5,
"advance": 4
},
"1": {
"x": 12,
"y": 24,
"w": 3,
"h": 5,
"advance": 4
},
"2": {
"x": 18,
"y": 24,
"w": 3,
"h": 5,
"advance": 4
},
"3": {
"x": 24,
"y": 24,
"w": 3,
"h": 5,
"advance": 4
},
"4": {
"x": 30,
"y": 24,
"w": 3,
"h": 5,
"advance": 4
},
"5": {
"x": 36,
"y": 24,
"w": 3,
"h": 5,
"advance": 4
},
"6": {
"x": 0,
"y": 30,
"w": 3,
"h": 5,
"advance": 4
},
"7": {
"x": 6,
"y": 30,
"w": 3,
"h": 5,
"advance": 4
},
"8": {
"x": 12,
"y": 30,
"w": 3,
"h": 5,
"advance": 4
},
"9": {
"x": 18,
"y": 30,
"w": 3,
"h": 5,
"advance": 4
},
":": {
"x": 6,
"y": 36,
"w": 1,
"h": 5,
"advance": 2
},
"?": {
"x": 0,
"y": 36,
"w": 3,
"h": 5,
"advance": 4
},
"A": {
"x": 0,
"y": 0,
"w": 3,
"h": 5,
"advance": 4
},
"B": {
"x": 6,
"y": 0,
"w": 3,
"h": 5,
"advance": 4
},
"C": {
"x": 12,
"y": 0,
"w": 3,
"h": 5,
"advance": 4
},
"D": {
"x": 18,
"y": 0,
"w": 3,
"h": 5,
"advance": 4
},
"E": {
"x": 24,
"y": 0,
"w": 3,
"h": 5,
"advance": 4
},
"F": {
"x": 30,
"y": 0,
"w": 3,
"h": 5,
"advance": 4
},
"G": {
"x": 36,
"y": 0,
"w": 4,
"h": 5,
"advance": 5
},
"H": {
"x": 0,
"y": 6,
"w": 3,
"h": 5,
"advance": 4
},
"I": {
"x": 6,
"y": 6,
"w": 3,
"h": 5,
"advance": 4
},
"J": {
"x": 12,
"y": 6,
"w": 3,
"h": 5,
"advance": 4
},
"K": {
"x": 18,
"y": 6,
"w": 3,
"h": 5,
"advance": 4
},
"L": {
"x": 24,
"y": 6,
"w": 3,
"h": 5,
"advance": 4
},
"M": {
"x": 30,
"y": 6,
"w": 5,
"h": 5,
"advance": 6
},
"N": {
"x": 36,
"y": 6,
"w": 4,
"h": 5,
"advance": 5
},
"O": {
"x": 0,
"y": 12,
"w": 3,
"h": 5,
"advance": 4
},
"P": {
"x": 6,
"y": 12,
"w": 3,
"h": 5,
"advance": 4
},
"Q": {
"x": 12,
"y": 12,
"w": 4,
"h": 5,
"advance": 5
},
"R": {
"x": 18,
"y": 12,
"w": 3,
"h": 5,
"advance": 4
},
"S": {
"x": 24,
"y": 12,
"w": 3,
"h": 5,
"advance": 4
},
"T": {
"x": 30,
"y": 12,
"w": 3,
"h": 5,
"advance": 4
},
"U": {
"x": 36,
"y": 12,
"w": 3,
"h": 5,
"advance": 4
},
"V": {
"x": 0,
"y": 18,
"w": 3,
"h": 5,
"advance": 4
},
"W": {
"x": 6,
"y": 18,
"w": 5,
"h": 5,
"advance": 6
},
"X": {
"x": 12,
"y": 18,
"w": 3,
"h": 5,
"advance": 4
},
"Y": {
"x": 18,
"y": 18,
"w": 3,
"h": 5,
"advance": 4
},
"Z": {
"x": 24,
"y": 18,
"w": 3,
"h": 5,
"advance": 4
},
"Ä": {
"x": 36,
"y": 18,
"w": 3,
"h": 5,
"advance": 4
},
"Å": {
"x": 30,
"y": 18,
"w": 3,
"h": 5,
"advance": 4
},
"Ö": {
"x": 0,
"y": 24,
"w": 3,
"h": 5,
"advance": 4
}
}
}

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# tiny5 - a 3x5 pixel font (uppercase + digits + Swedish ÅÄÖ).
# Widths vary: M/W are 5 px, punctuation as narrow as 1 px.
font: tiny5
spacing: 1
space-width: 3
glyph A:
.#.
#.#
###
#.#
#.#
glyph B:
##.
#.#
##.
#.#
##.
glyph C:
.##
#..
#..
#..
.##
glyph D:
##.
#.#
#.#
#.#
##.
glyph E:
###
#..
##.
#..
###
glyph F:
###
#..
##.
#..
#..
glyph G:
.###
#...
#.##
#..#
.##.
glyph H:
#.#
#.#
###
#.#
#.#
glyph I:
###
.#.
.#.
.#.
###
glyph J:
..#
..#
..#
#.#
.#.
glyph K:
#.#
#.#
##.
#.#
#.#
glyph L:
#..
#..
#..
#..
###
glyph M:
#...#
##.##
#.#.#
#...#
#...#
glyph N:
#..#
##.#
#.##
#..#
#..#
glyph O:
.#.
#.#
#.#
#.#
.#.
glyph P:
##.
#.#
##.
#..
#..
glyph Q:
.##.
#..#
#..#
#.#.
.#.#
glyph R:
##.
#.#
##.
#.#
#.#
glyph S:
.##
#..
.#.
..#
##.
glyph T:
###
.#.
.#.
.#.
.#.
glyph U:
#.#
#.#
#.#
#.#
###
glyph V:
#.#
#.#
#.#
#.#
.#.
glyph W:
#...#
#...#
#.#.#
##.##
#...#
glyph X:
#.#
#.#
.#.
#.#
#.#
glyph Y:
#.#
#.#
.#.
.#.
.#.
glyph Z:
###
..#
.#.
#..
###
glyph Å:
.#.
.#.
#.#
###
#.#
glyph Ä:
#.#
.#.
#.#
###
#.#
glyph Ö:
#.#
.#.
#.#
#.#
.#.
glyph 0:
###
#.#
#.#
#.#
###
glyph 1:
.#.
##.
.#.
.#.
###
glyph 2:
##.
..#
.#.
#..
###
glyph 3:
###
..#
.##
..#
###
glyph 4:
#.#
#.#
###
..#
..#
glyph 5:
###
#..
##.
..#
##.
glyph 6:
.##
#..
###
#.#
###
glyph 7:
###
..#
.#.
.#.
.#.
glyph 8:
###
#.#
###
#.#
###
glyph 9:
###
#.#
###
..#
##.
glyph .:
.
.
.
.
#
glyph ,:
..
..
..
.#
#.
glyph !:
#
#
#
.
#
glyph ?:
###
..#
.#.
...
.#.
glyph ::
.
#
.
#
.
glyph -:
...
...
###
...
...
glyph +:
...
.#.
###
.#.
...
glyph ':
#
#
.
.
.

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// Package font parses .font text files and renders bitmap fonts to
// atlases (PNG + JSON metrics) and text images.
package font
import (
"bufio"
"fmt"
"io"
"os"
"path/filepath"
"sort"
"strconv"
"strings"
)
// MaxGlyphSize bounds glyph width/height in pixels.
const MaxGlyphSize = 64
// Glyph is one character's bitmap: rows of booleans (true = pixel on).
// All glyphs in a font share the same height; widths vary
// (proportional fonts).
type Glyph struct {
Char rune
W, H int
Rows [][]bool
}
// Font is a parsed .font file.
type Font struct {
Name string
Height int // glyph height, uniform across the font
LineHeight int // suggested distance between text baselines
Baseline int // rows from glyph top to the baseline
Spacing int // horizontal px between glyphs
SpaceWidth int // advance of ' '
Glyphs map[rune]*Glyph
Order []rune // file order, for stable atlas layout
}
// ParseFile reads a .font file; the font name defaults to the file name.
func ParseFile(path string) (*Font, error) {
f, err := os.Open(path)
if err != nil {
return nil, err
}
defer f.Close()
ft, err := Parse(f)
if err != nil {
return nil, fmt.Errorf("%s: %w", path, err)
}
if ft.Name == "" {
ft.Name = strings.TrimSuffix(filepath.Base(path), filepath.Ext(path))
}
return ft, nil
}
// Parse reads the .font text format:
//
// # comment
// font: tiny5 optional name
// spacing: 1 px between glyphs (default 1)
// space-width: 3 advance of ' ' (default: width of '0' or 3)
// line-height: 7 default: glyph height + 1
// baseline: 5 default: glyph height
//
// glyph A:
// .#.
// #.#
// ###
// #.#
// #.#
//
// Glyph grids use '#' for on and '.' for off. Every glyph must have the
// same height; widths may differ. The char between "glyph " and the
// trailing ':' is taken literally (one character, e.g. "glyph ::").
func Parse(r io.Reader) (*Font, error) {
ft := &Font{
Spacing: 1,
SpaceWidth: -1, // resolved in validate
LineHeight: -1,
Baseline: -1,
Glyphs: map[rune]*Glyph{},
}
var cur *Glyph
sc := bufio.NewScanner(r)
sc.Buffer(make([]byte, 0, 64*1024), 1024*1024)
lineNo := 0
flush := func() error {
if cur == nil {
return nil
}
if len(cur.Rows) == 0 {
return fmt.Errorf("glyph %q has no grid rows", string(cur.Char))
}
cur.H = len(cur.Rows)
cur.W = len(cur.Rows[0])
for i, row := range cur.Rows {
if len(row) != cur.W {
return fmt.Errorf("glyph %q row %d is %d px wide, expected %d", string(cur.Char), i+1, len(row), cur.W)
}
}
if cur.W > MaxGlyphSize || cur.H > MaxGlyphSize {
return fmt.Errorf("glyph %q is %dx%d; the maximum is %dx%d", string(cur.Char), cur.W, cur.H, MaxGlyphSize, MaxGlyphSize)
}
if _, dup := ft.Glyphs[cur.Char]; dup {
return fmt.Errorf("glyph %q defined twice", string(cur.Char))
}
ft.Glyphs[cur.Char] = cur
ft.Order = append(ft.Order, cur.Char)
cur = nil
return nil
}
for sc.Scan() {
lineNo++
line := strings.TrimSpace(sc.Text())
if line == "" {
continue
}
// '#' starts a comment — except inside a glyph where a line of
// only '#'/'.' is a grid row.
if strings.HasPrefix(line, "#") && !(cur != nil && isGridLine(line)) {
continue
}
if strings.HasPrefix(strings.ToLower(line), "glyph ") && strings.HasSuffix(line, ":") {
if err := flush(); err != nil {
return nil, fmt.Errorf("line %d: %w", lineNo, err)
}
name := strings.TrimSuffix(line[len("glyph "):], ":")
runes := []rune(name)
if len(runes) != 1 {
return nil, fmt.Errorf("line %d: glyph name %q must be exactly one character", lineNo, name)
}
cur = &Glyph{Char: runes[0]}
continue
}
if cur != nil && isGridLine(line) {
row := make([]bool, 0, len(line))
for _, r := range line {
row = append(row, r == '#')
}
cur.Rows = append(cur.Rows, row)
continue
}
// header key: value
if i := strings.Index(line, ":"); i > 0 && cur == nil {
key := strings.ToLower(strings.TrimSpace(line[:i]))
val := strings.TrimSpace(line[i+1:])
var err error
switch key {
case "font":
ft.Name = val
case "spacing":
ft.Spacing, err = strconv.Atoi(val)
case "space-width":
ft.SpaceWidth, err = strconv.Atoi(val)
case "line-height":
ft.LineHeight, err = strconv.Atoi(val)
case "baseline":
ft.Baseline, err = strconv.Atoi(val)
default:
return nil, fmt.Errorf("line %d: unknown setting %q", lineNo, key)
}
if err != nil {
return nil, fmt.Errorf("line %d: %s: %v", lineNo, key, err)
}
continue
}
return nil, fmt.Errorf("line %d: unexpected %q (want 'key: value', 'glyph X:' or a #/. grid row)", lineNo, line)
}
if err := sc.Err(); err != nil {
return nil, err
}
if err := flush(); err != nil {
return nil, err
}
return ft, ft.validate()
}
// isGridLine reports whether the line consists solely of '#' and '.'.
func isGridLine(s string) bool {
if s == "" {
return false
}
for _, r := range s {
if r != '#' && r != '.' {
return false
}
}
return true
}
func (ft *Font) validate() error {
if len(ft.Order) == 0 {
return fmt.Errorf("font has no glyphs")
}
ft.Height = ft.Glyphs[ft.Order[0]].H
for _, r := range ft.Order {
if g := ft.Glyphs[r]; g.H != ft.Height {
return fmt.Errorf("glyph %q is %d px tall but %q is %d — all glyphs must share one height",
string(r), g.H, string(ft.Order[0]), ft.Height)
}
}
if ft.LineHeight < 0 {
ft.LineHeight = ft.Height + 1
}
if ft.Baseline < 0 {
ft.Baseline = ft.Height
}
if ft.SpaceWidth < 0 {
if g, ok := ft.Glyphs['0']; ok {
ft.SpaceWidth = g.W
} else {
ft.SpaceWidth = 3
}
}
if ft.Spacing < 0 {
return fmt.Errorf("spacing must be >= 0")
}
return nil
}
// MaxGlyphWidth returns the widest glyph's width.
func (ft *Font) MaxGlyphWidth() int {
w := 0
for _, r := range ft.Order {
if g := ft.Glyphs[r]; g.W > w {
w = g.W
}
}
return w
}
// SortedChars returns the glyph chars sorted by codepoint (JSON stability).
func (ft *Font) SortedChars() []rune {
out := append([]rune(nil), ft.Order...)
sort.Slice(out, func(i, j int) bool { return out[i] < out[j] })
return out
}

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package font
import (
"bytes"
"encoding/json"
"image/color"
"strings"
"testing"
)
const tiny = `
font: t
spacing: 1
space-width: 2
glyph A:
.#.
#.#
###
glyph I:
#
#
#
`
func parseOK(t *testing.T, src string) *Font {
t.Helper()
ft, err := Parse(strings.NewReader(src))
if err != nil {
t.Fatalf("parse: %v", err)
}
return ft
}
func TestParseBasics(t *testing.T) {
ft := parseOK(t, tiny)
if ft.Name != "t" || ft.Height != 3 || len(ft.Order) != 2 {
t.Errorf("name=%q height=%d glyphs=%d", ft.Name, ft.Height, len(ft.Order))
}
a := ft.Glyphs['A']
if a.W != 3 || a.H != 3 {
t.Errorf("A is %dx%d, want 3x3", a.W, a.H)
}
if !a.Rows[1][0] || a.Rows[0][0] {
t.Error("A pixel pattern wrong")
}
i := ft.Glyphs['I']
if i.W != 1 {
t.Errorf("I width = %d, want 1 (proportional)", i.W)
}
if ft.LineHeight != 4 || ft.Baseline != 3 {
t.Errorf("defaults: lineHeight=%d baseline=%d", ft.LineHeight, ft.Baseline)
}
}
func TestParseErrors(t *testing.T) {
cases := map[string]string{
"no glyphs": "font: x\n",
"ragged glyph": "glyph A:\n##\n#\n",
"height differs": "glyph A:\n#\n#\n\nglyph B:\n#\n",
"dup glyph": "glyph A:\n#\n\nglyph A:\n#\n",
"bad name": "glyph AB:\n#\n",
"unknown key": "wat: 3\nglyph A:\n#\n",
}
for name, src := range cases {
if _, err := Parse(strings.NewReader(src)); err == nil {
t.Errorf("%s: expected error", name)
}
}
}
func TestGlyphNameColon(t *testing.T) {
ft := parseOK(t, "glyph ::\n#\n#\n")
if _, ok := ft.Glyphs[':']; !ok {
t.Error("glyph ':' not parsed")
}
}
func TestAtlasAndMetrics(t *testing.T) {
ft := parseOK(t, tiny)
img, m := ft.BuildAtlas("t.png")
if m.Glyphs["A"].Advance != 4 {
t.Errorf("A advance = %d, want 4 (w3 + spacing1)", m.Glyphs["A"].Advance)
}
g := m.Glyphs["A"]
// center-top pixel of A within its atlas cell: (x+1, y+0)
if img.NRGBAAt(g.X+1, g.Y).A == 0 {
t.Error("A apex pixel missing in atlas")
}
if img.NRGBAAt(g.X, g.Y).A != 0 {
t.Error("A corner should be empty")
}
var buf bytes.Buffer
if err := WriteMetrics(&buf, m); err != nil {
t.Fatal(err)
}
var back Metrics
if err := json.Unmarshal(buf.Bytes(), &back); err != nil {
t.Fatalf("metrics json invalid: %v", err)
}
if back.Glyphs["I"].W != 1 {
t.Errorf("metrics roundtrip: I.w = %d", back.Glyphs["I"].W)
}
}
func TestRenderText(t *testing.T) {
ft := parseOK(t, tiny)
white := color.NRGBA{255, 255, 255, 255}
img, warns := ft.RenderText("AI", 1, white)
if len(warns) != 0 {
t.Errorf("warnings: %v", warns)
}
// width: A(3) + spacing(1) + I(1) = 5
if b := img.Bounds(); b.Dx() != 5 || b.Dy() != 3 {
t.Errorf("size = %dx%d, want 5x3", b.Dx(), b.Dy())
}
// I column at x=4
if img.NRGBAAt(4, 0).A == 0 {
t.Error("I pixel missing")
}
_, warns = ft.RenderText("AXA", 1, white)
if len(warns) != 1 {
t.Errorf("missing-glyph warning expected, got %v", warns)
}
img, _ = ft.RenderText(`A\nA`, 1, white)
if b := img.Bounds(); b.Dy() != ft.LineHeight+ft.Height {
t.Errorf("two-line height = %d, want %d", b.Dy(), ft.LineHeight+ft.Height)
}
img2, _ := ft.RenderText("A", 3, white)
if b := img2.Bounds(); b.Dx() != 9 || b.Dy() != 9 {
t.Errorf("scaled size = %dx%d, want 9x9", b.Dx(), b.Dy())
}
}
func TestSpaceWidthDefaultFromZero(t *testing.T) {
ft := parseOK(t, "glyph 0:\n####\n####\n")
if ft.SpaceWidth != 4 {
t.Errorf("space-width = %d, want 4 (width of '0')", ft.SpaceWidth)
}
}

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@@ -0,0 +1,165 @@
package font
import (
"encoding/json"
"fmt"
"image"
"image/color"
"image/png"
"io"
"strings"
)
// AtlasGlyph is one glyph's placement in the atlas.
type AtlasGlyph struct {
X int `json:"x"`
Y int `json:"y"`
W int `json:"w"`
H int `json:"h"`
Advance int `json:"advance"` // cursor movement after drawing: W + spacing
}
// Metrics is the JSON sidecar written next to the atlas PNG.
type Metrics struct {
Name string `json:"name"`
Atlas string `json:"atlas"`
Height int `json:"height"`
LineHeight int `json:"lineHeight"`
Baseline int `json:"baseline"`
Spacing int `json:"spacing"`
SpaceWidth int `json:"spaceWidth"`
Glyphs map[string]AtlasGlyph `json:"glyphs"`
}
// BuildAtlas packs all glyphs into a grid atlas image (white pixels on
// transparency, so game engines can tint) and returns the metrics.
// atlasName is stored in the metrics so loaders can find the image.
func (ft *Font) BuildAtlas(atlasName string) (*image.NRGBA, *Metrics) {
n := len(ft.Order)
cols := 1
for cols*cols < n {
cols++
}
rows := (n + cols - 1) / cols
cellW := ft.MaxGlyphWidth() + 1 // 1 px padding against bleed
cellH := ft.Height + 1
img := image.NewNRGBA(image.Rect(0, 0, cols*cellW, rows*cellH))
white := color.NRGBA{255, 255, 255, 255}
m := &Metrics{
Name: ft.Name,
Atlas: atlasName,
Height: ft.Height,
LineHeight: ft.LineHeight,
Baseline: ft.Baseline,
Spacing: ft.Spacing,
SpaceWidth: ft.SpaceWidth,
Glyphs: map[string]AtlasGlyph{},
}
for i, r := range ft.Order {
g := ft.Glyphs[r]
x0 := (i % cols) * cellW
y0 := (i / cols) * cellH
drawGlyph(img, g, x0, y0, white)
m.Glyphs[string(r)] = AtlasGlyph{X: x0, Y: y0, W: g.W, H: g.H, Advance: g.W + ft.Spacing}
}
return img, m
}
func drawGlyph(img *image.NRGBA, g *Glyph, x0, y0 int, c color.NRGBA) {
for y, row := range g.Rows {
for x, on := range row {
if on {
img.SetNRGBA(x0+x, y0+y, c)
}
}
}
}
// RenderText draws text into a new image using the font. scale is an
// integer upscale factor; unknown characters are skipped with a warning
// returned. "\n" (literal backslash-n) and real newlines both break lines.
func (ft *Font) RenderText(text string, scale int, fg color.NRGBA) (*image.NRGBA, []string) {
if scale < 1 {
scale = 1
}
text = strings.ReplaceAll(text, `\n`, "\n")
lines := strings.Split(text, "\n")
var warnings []string
width := 0
for _, line := range lines {
if w := ft.lineWidth(line); w > width {
width = w
}
}
if width == 0 {
width = 1
}
height := ft.LineHeight*(len(lines)-1) + ft.Height
small := image.NewNRGBA(image.Rect(0, 0, width, height))
for li, line := range lines {
x := 0
y := li * ft.LineHeight
for _, r := range line {
if r == ' ' {
x += ft.SpaceWidth + ft.Spacing
continue
}
g, ok := ft.Glyphs[r]
if !ok {
warnings = append(warnings, fmt.Sprintf("no glyph for %q — skipped", string(r)))
x += ft.SpaceWidth + ft.Spacing
continue
}
drawGlyph(small, g, x, y, fg)
x += g.W + ft.Spacing
}
}
if scale == 1 {
return small, warnings
}
b := small.Bounds()
big := image.NewNRGBA(image.Rect(0, 0, b.Dx()*scale, b.Dy()*scale))
for y := 0; y < b.Dy(); y++ {
for x := 0; x < b.Dx(); x++ {
c := small.NRGBAAt(x, y)
for dy := 0; dy < scale; dy++ {
for dx := 0; dx < scale; dx++ {
big.SetNRGBA(x*scale+dx, y*scale+dy, c)
}
}
}
}
return big, warnings
}
func (ft *Font) lineWidth(line string) int {
x := 0
for _, r := range line {
if r == ' ' {
x += ft.SpaceWidth + ft.Spacing
continue
}
if g, ok := ft.Glyphs[r]; ok {
x += g.W + ft.Spacing
} else {
x += ft.SpaceWidth + ft.Spacing
}
}
if x > 0 {
x -= ft.Spacing // no trailing spacing
}
return x
}
// WritePNG encodes an image as PNG.
func WritePNG(w io.Writer, img image.Image) error { return png.Encode(w, img) }
// WriteMetrics encodes metrics as indented JSON.
func WriteMetrics(w io.Writer, m *Metrics) error {
enc := json.NewEncoder(w)
enc.SetIndent("", " ")
return enc.Encode(m)
}

3
bitmap-font-maker/go.mod Normal file
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@@ -0,0 +1,3 @@
module gitea.brasse-pc.eu/brasse/agent-tools/bitmap-font-maker
go 1.24

258
bitmap-font-maker/main.go Normal file
View File

@@ -0,0 +1,258 @@
// fontc turns .font text files (pixel glyph grids) into font atlases
// (PNG + JSON metrics) and renders text strings to images.
package main
import (
"flag"
"fmt"
"image/color"
"os"
"path/filepath"
"strings"
"gitea.brasse-pc.eu/brasse/agent-tools/bitmap-font-maker/font"
)
var version = "dev"
const usage = `fontc - bitmap font maker for agents
Usage:
fontc build <file.font> [flags] build atlas PNG + metrics JSON
fontc render <file.font> <text> [flags]
render a text string to PNG
fontc info <file.font> validate + list glyphs
fontc preview <file.font> <text> draw text in the terminal
fontc version
Build flags:
-o <base> output base name -> <base>.png + <base>.json
(default: font file name without extension)
Render flags:
-o <path> output PNG (default text.png)
--scale <n> integer upscale, default 1
--color <c> text color (#RRGGBB, CSS names not supported here), default #FFFFFF
Use \n in <text> for line breaks.
The .font format:
font: tiny5 optional name
spacing: 1 px between glyphs (default 1)
space-width: 3 advance of ' ' (default: width of '0')
line-height: 7 default: glyph height + 1
baseline: 5 default: glyph height
glyph A:
.#.
#.#
###
#.#
#.#
'#' = pixel on, '.' = off. All glyphs share one height; widths may
differ (proportional). The atlas draws glyphs in white so engines can
tint them; metrics JSON carries x/y/w/h/advance per glyph.
`
func main() {
if len(os.Args) < 2 {
fmt.Print(usage)
os.Exit(2)
}
switch os.Args[1] {
case "build":
cmdBuild(os.Args[2:])
case "render":
cmdRender(os.Args[2:])
case "info":
cmdInfo(os.Args[2:])
case "preview":
cmdPreview(os.Args[2:])
case "version", "--version", "-v":
fmt.Println("fontc", version)
case "help", "--help", "-h":
fmt.Print(usage)
default:
die("unknown command %q — run 'fontc 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 cmdBuild(args []string) {
fs := flag.NewFlagSet("build", flag.ExitOnError)
out := fs.String("o", "", "output base name")
parseInterspersed(fs, args)
if fs.NArg() != 1 {
die("build takes exactly one .font file")
}
ft, err := font.ParseFile(fs.Arg(0))
if err != nil {
die("%v", err)
}
base := *out
if base == "" {
base = strings.TrimSuffix(fs.Arg(0), filepath.Ext(fs.Arg(0)))
}
base = strings.TrimSuffix(base, ".png")
img, metrics := ft.BuildAtlas(filepath.Base(base) + ".png")
pngF, err := os.Create(base + ".png")
if err != nil {
die("%v", err)
}
defer pngF.Close()
if err := font.WritePNG(pngF, img); err != nil {
die("%v", err)
}
jsonF, err := os.Create(base + ".json")
if err != nil {
die("%v", err)
}
defer jsonF.Close()
if err := font.WriteMetrics(jsonF, metrics); err != nil {
die("%v", err)
}
b := img.Bounds()
fmt.Printf("%s.png (%dx%d atlas, %d glyphs)\n%s.json\n", base, b.Dx(), b.Dy(), len(ft.Order), base)
}
func parseHexColor(s string) (r, g, b uint8, err error) {
s = strings.TrimPrefix(strings.TrimSpace(s), "#")
if len(s) != 6 {
return 0, 0, 0, fmt.Errorf("color must be #RRGGBB, got %q", s)
}
var v [3]uint8
for i := 0; i < 3; i++ {
var n int
if _, err := fmt.Sscanf(s[i*2:i*2+2], "%02x", &n); err != nil {
return 0, 0, 0, fmt.Errorf("bad hex color %q", s)
}
v[i] = uint8(n)
}
return v[0], v[1], v[2], nil
}
func cmdRender(args []string) {
fs := flag.NewFlagSet("render", flag.ExitOnError)
out := fs.String("o", "text.png", "output PNG")
scale := fs.Int("scale", 1, "integer upscale")
col := fs.String("color", "#FFFFFF", "text color #RRGGBB")
parseInterspersed(fs, args)
if fs.NArg() != 2 {
die("render takes a .font file and a text string")
}
ft, err := font.ParseFile(fs.Arg(0))
if err != nil {
die("%v", err)
}
r, g, b, err := parseHexColor(*col)
if err != nil {
die("%v", err)
}
img, warnings := ft.RenderText(fs.Arg(1), *scale, rgba(r, g, b))
for _, w := range warnings {
fmt.Fprintln(os.Stderr, "fontc:", w)
}
f, err := os.Create(*out)
if err != nil {
die("%v", err)
}
defer f.Close()
if err := font.WritePNG(f, img); err != nil {
die("%v", err)
}
bd := img.Bounds()
fmt.Printf("%s (%dx%d px)\n", *out, bd.Dx(), bd.Dy())
}
func cmdInfo(args []string) {
if len(args) != 1 {
die("info takes exactly one .font file")
}
ft, err := font.ParseFile(args[0])
if err != nil {
die("%v", err)
}
fmt.Printf("font: %s\n", ft.Name)
fmt.Printf("height: %d px\n", ft.Height)
fmt.Printf("line-height: %d px\n", ft.LineHeight)
fmt.Printf("baseline: %d\n", ft.Baseline)
fmt.Printf("spacing: %d px\n", ft.Spacing)
fmt.Printf("space-width: %d px\n", ft.SpaceWidth)
fmt.Printf("glyphs: %d\n", len(ft.Order))
var chars []string
for _, r := range ft.SortedChars() {
chars = append(chars, string(r))
}
fmt.Printf(" %s\n", strings.Join(chars, " "))
fmt.Println("valid: yes")
}
func cmdPreview(args []string) {
if len(args) != 2 {
die("preview takes a .font file and a text string")
}
ft, err := font.ParseFile(args[0])
if err != nil {
die("%v", err)
}
img, warnings := ft.RenderText(args[1], 1, rgba(255, 255, 255))
for _, w := range warnings {
fmt.Fprintln(os.Stderr, "fontc:", w)
}
b := img.Bounds()
for y := 0; y < b.Dy(); y += 2 {
var sb strings.Builder
for x := 0; x < b.Dx(); x++ {
top := img.NRGBAAt(x, y).A >= 128
bot := y+1 < b.Dy() && img.NRGBAAt(x, y+1).A >= 128
switch {
case top && bot:
sb.WriteRune('█')
case top:
sb.WriteRune('▀')
case bot:
sb.WriteRune('▄')
default:
sb.WriteByte(' ')
}
}
fmt.Println(sb.String())
}
}
func rgba(r, g, b uint8) color.NRGBA {
return color.NRGBA{R: r, G: g, B: b, A: 255}
}
func die(format string, a ...any) {
fmt.Fprintf(os.Stderr, "fontc: "+format+"\n", a...)
os.Exit(1)
}