feat: add dithering param and parallel frame rendering for GIF

- Add dithering bool param to GIFRequest (default true)
- Parallelize frame rendering with goroutines
- Conditional Floyd-Steinberg dithering for speed vs quality tradeoff

internal/api/handlers.go

@@ -103,7 +103,7 @@ func (h *Handlers) HandleGIF(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	gifBytes, err := render.RenderGIF(result.GLBBytes, result.Atlas, req.Background, req.Frames, req.Width, req.Height, req.Delay)
+	gifBytes, err := render.RenderGIF(result.GLBBytes, result.Atlas, req.Background, req.Frames, req.Width, req.Height, req.Delay, *req.Dithering)
 	if err != nil {
 		writeError(w, http.StatusInternalServerError, "render failed: "+err.Error())
 		return

internal/api/openapi.go

@@ -200,7 +200,8 @@ const OpenAPISpec = `{
           "frames": {"type": "integer", "default": 36, "description": "Number of frames (36 = 10° per frame)"},
           "width": {"type": "integer", "default": 512, "description": "Image width in pixels"},
           "height": {"type": "integer", "default": 512, "description": "Image height in pixels"},
-          "delay": {"type": "integer", "default": 5, "description": "Centiseconds between frames"}
+          "delay": {"type": "integer", "default": 5, "description": "Centiseconds between frames"},
+          "dithering": {"type": "boolean", "default": true, "description": "Enable Floyd-Steinberg dithering (disable for faster rendering)"}
         }
       },
       "ErrorResponse": {

internal/api/types.go

@@ -19,6 +19,7 @@ type GIFRequest struct {
 	Width      int             `json:"width"`      // default 512
 	Height     int             `json:"height"`     // default 512
 	Delay      int             `json:"delay"`      // centiseconds between frames, default 5
+	Dithering  *bool           `json:"dithering"`  // Floyd-Steinberg dithering, default true
 }
 
 // ErrorResponse represents an error returned by the API
@@ -56,4 +57,8 @@ func (r *GIFRequest) ApplyDefaults() {
 	if r.Background == "" {
 		r.Background = "#FFFFFF"
 	}
+	if r.Dithering == nil {
+		defaultDithering := true
+		r.Dithering = &defaultDithering
+	}
 }

internal/render/gif.go

@@ -7,12 +7,13 @@ import (
 	"image/color/palette"
 	"image/draw"
 	"image/gif"
+	"sync"
 
 	"github.com/hytale-tools/blockymodel-merger/pkg/texture"
 )
 
 // RenderGIF renders a GLB model to an animated GIF rotating 360 degrees
-func RenderGIF(glbBytes []byte, atlas *texture.Atlas, background string, frames, width, height, delay int) ([]byte, error) {
+func RenderGIF(glbBytes []byte, atlas *texture.Atlas, background string, frames, width, height, delay int, dithering bool) ([]byte, error) {
 	// Parse background color
 	bgColor, err := ParseHexColor(background)
 	if err != nil {
@@ -38,20 +39,30 @@ func RenderGIF(glbBytes []byte, atlas *texture.Atlas, background string, frames,
 		LoopCount: 0, // 0 = infinite loop
 	}
 
-	// Render each frame
+	// Render frames in parallel
+	var wg sync.WaitGroup
 	for i := 0; i < frames; i++ {
-		rotation := float64(i) * rotationPerFrame
+		wg.Add(1)
+		go func(frameIdx int) {
+			defer wg.Done()
+			rotation := float64(frameIdx) * rotationPerFrame
 
-		// Render frame
-		img := RenderScene(mesh, atlasImage, rotation, width, height, bgColor)
+			// Render frame
+			img := RenderScene(mesh, atlasImage, rotation, width, height, bgColor)
 
-		// Quantize to palette
-		paletted := image.NewPaletted(img.Bounds(), palette.Plan9)
-		draw.FloydSteinberg.Draw(paletted, img.Bounds(), img, image.Point{})
+			// Quantize to palette
+			paletted := image.NewPaletted(img.Bounds(), palette.Plan9)
+			if dithering {
+				draw.FloydSteinberg.Draw(paletted, img.Bounds(), img, image.Point{})
+			} else {
+				draw.Draw(paletted, img.Bounds(), img, image.Point{}, draw.Src)
+			}
 
-		g.Image[i] = paletted
-		g.Delay[i] = delay
+			g.Image[frameIdx] = paletted
+			g.Delay[frameIdx] = delay
+		}(i)
 	}
+	wg.Wait()
 
 	// Encode GIF
 	var buf bytes.Buffer