Add support for decoding an animated WebP

The initial implementation doesn't fully expose `WebPAnimDecoderOptions`.

webp/anim_decode.go

@@ -0,0 +1,123 @@
+package webp
+
+/*
+#cgo LDFLAGS: -lwebpdemux
+
+#include <stdlib.h>
+#include <webp/demux.h>
+*/
+import "C"
+
+import (
+	"encoding/binary"
+	"errors"
+	"image"
+	"image/color"
+	"unsafe"
+)
+
+// AnimationDecoder decodes an animated WebP.
+type AnimationDecoder struct {
+	opts  C.WebPAnimDecoderOptions
+	c     *C.WebPAnimDecoder
+	cData *C.WebPData
+}
+
+// AnimationInfo represents properties of an animation.
+type AnimationInfo struct {
+	CanvasWidth     int
+	CanvasHeight    int
+	LoopCount       int
+	FrameCount      int
+	BackgroundColor color.RGBA
+}
+
+// Animation represents a decoded WebP animation.
+type Animation struct {
+	AnimationInfo
+
+	// Image is the list of decoded frames.
+	Image []*image.RGBA
+
+	// Timestamp of each frame in milliseconds.
+	Timestamp []int
+}
+
+// NewAnimationDecoder initializes a new decoder.
+func NewAnimationDecoder(data []byte) (*AnimationDecoder, error) {
+	ad := &AnimationDecoder{}
+
+	if C.WebPAnimDecoderOptionsInit(&ad.opts) == 0 {
+		return nil, errors.New("failed to initialize animation decoder config")
+	}
+	ad.opts.color_mode = C.MODE_RGBA
+
+	ad.cData = &C.WebPData{}
+	C.WebPDataInit(ad.cData)
+
+	ad.cData.bytes = (*C.uint8_t)(C.CBytes(data))
+	ad.cData.size = (C.size_t)(len(data))
+
+	ad.c = C.WebPAnimDecoderNew(ad.cData, &ad.opts)
+	if ad.c == nil {
+		C.free(unsafe.Pointer(ad.cData.bytes))
+		return nil, errors.New("failed to initialize animation decoder")
+	}
+
+	return ad, nil
+}
+
+// GetInfo retrieves properties of the animation.
+func (ad *AnimationDecoder) GetInfo() (*AnimationInfo, error) {
+	info := &C.WebPAnimInfo{}
+
+	if C.WebPAnimDecoderGetInfo(ad.c, info) == 0 {
+		return nil, errors.New("error in WebPAnimDecoderGetInfo")
+	}
+
+	b := make([]uint8, 4)
+	binary.BigEndian.PutUint32(b, uint32(info.bgcolor))
+
+	return &AnimationInfo{
+		CanvasWidth:     int(info.canvas_width),
+		CanvasHeight:    int(info.canvas_height),
+		LoopCount:       int(info.loop_count),
+		FrameCount:      int(info.frame_count),
+		BackgroundColor: color.RGBA{b[0], b[1], b[2], b[3]},
+	}, nil
+}
+
+// Decode decodes a WebP animation.
+func (ad *AnimationDecoder) Decode() (*Animation, error) {
+	info, err := ad.GetInfo()
+	if err != nil {
+		return nil, err
+	}
+
+	anim := &Animation{
+		AnimationInfo: *info,
+	}
+
+	for C.WebPAnimDecoderHasMoreFrames(ad.c) != 0 {
+		var ts C.int
+		var pix *C.uint8_t
+
+		if C.WebPAnimDecoderGetNext(ad.c, &pix, &ts) == 0 {
+			return nil, errors.New("error in WebPAnimDecoderGetNext")
+		}
+
+		img := image.NewRGBA(image.Rect(0, 0, info.CanvasWidth, info.CanvasHeight))
+		C.memcpy(unsafe.Pointer(&img.Pix[0]), unsafe.Pointer(pix), C.size_t(len(img.Pix)))
+
+		anim.Image = append(anim.Image, img)
+		anim.Timestamp = append(anim.Timestamp, int(ts))
+	}
+
+	return anim, nil
+}
+
+// Close deletes the decoder and frees resources.
+func (ad *AnimationDecoder) Close() {
+	C.free(unsafe.Pointer(ad.cData.bytes))
+	C.WebPAnimDecoderDelete(ad.c)
+}