pixel-sprite-maker: spritec - .sprite text format -> png/jpg/svg + sprite sheets

- .sprite format: single-char palette keys (hex/rgb()/CSS names/none), grid
  rows, '.' transparent by default, max 256x256 per sprite
- render/sheet/info/preview subcommands; sheets name themselves
  <base>_<cellW>x<cellH>_<cols>x<rows>.<ext> (row-major)
- SVG output RLE-merges pixel runs; JPG composites over --bg
- go tests for parser, colors, scaling, svg, sheet layout

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

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)
+}