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/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
+}