initial commit

main.go

@@ -0,0 +1,76 @@
+//go:build js && wasm
+// +build js,wasm
+
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"image"
+	"image/color/palette"
+	"image/draw"
+	"image/gif"
+	"image/png"
+	"log"
+	"syscall/js"
+)
+
+func encodeGif(this js.Value, args []js.Value) interface{} {
+	inImages := args[0]
+	delays := args[1]
+	disposals := args[2]
+
+	outImages := make([]*image.Paletted, 0)
+	delay := make([]int, 0)
+	disposal := make([]byte, 0)
+
+	// Plan9 palette doesn't include transparent colors
+	// so we use WebSafe and add transparent color
+	myPalette := append(palette.WebSafe, image.Transparent)
+	opts := gif.Options{
+		NumColors: 256,
+		Drawer:    draw.FloydSteinberg,
+	}
+
+	fmt.Println(inImages.Length())
+	for i := 0; i < inImages.Length(); i++ {
+		imgBytes := make([]byte, inImages.Index(i).Length())
+		js.CopyBytesToGo(imgBytes, inImages.Index(i))
+
+		reader := bytes.NewReader(imgBytes)
+		img, err := png.Decode(reader)
+		if err != nil {
+			log.Fatal(err)
+		}
+
+		b := img.Bounds()
+		pimg := image.NewPaletted(b, myPalette)
+		opts.Drawer.Draw(pimg, b, img, image.ZP)
+
+		outImages = append(outImages, pimg)
+		delay = append(delay, delays.Index(i).Int())
+		disposal = append(disposal, byte(disposals.Index(i).Int()))
+	}
+
+	outGif := &gif.GIF{
+		Image:           outImages,
+		Delay:           delay,
+		LoopCount:       0,
+		Disposal:        disposal,
+		BackgroundIndex: 0,
+	}
+
+	outBytes := new(bytes.Buffer)
+	err := gif.EncodeAll(outBytes, outGif)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	return js.CopyBytesToJS(args[3], outBytes.Bytes())
+}
+
+func main() {
+	done := make(chan struct{}, 0)
+	js.Global().Set("encodeGif", js.FuncOf(encodeGif))
+	<-done
+}