Add documentation and tests for animation

Makefile

@@ -16,7 +16,7 @@ $(libwebp_so):
 	&& wget http://downloads.webmproject.org/releases/webp/libwebp-$(LIBWEBP_VERSION).tar.gz \
 	&& tar xf libwebp-$(LIBWEBP_VERSION).tar.gz \
 	&& cd libwebp-$(LIBWEBP_VERSION) \
-	&& ./configure --prefix=$(LIBWEBP_PREFIX) \
+	&& ./configure --prefix=$(LIBWEBP_PREFIX) --enable-libwebpmux \
 	&& make \
 	&& make install
 

README.md

@@ -8,7 +8,7 @@ A implementation of Go binding for [libwebp](https://developers.google.com/speed
 
 ## Dependencies
 
-- libwebp 0.4, 0.5
+- libwebp 0.4, 0.5+, compiled with `--enable-libwebpmux`
 
 ## Usage
 
@@ -76,10 +76,66 @@ func main() {
 }
 ```
 
+
+### Encoding animations from a series of frames
+
+```
+package main
+
+import (
+	"image"
+	"time"
+
+	"github.com/harukasan/go-libwebp/test/util"
+	"github.com/harukasan/go-libwebp/webp"
+)
+
+func main() {
+	// Get some frames
+	img := []image.Image{
+		util.ReadPNG("butterfly.png"),
+		util.ReadPNG("checkerboard.png"),
+		util.ReadPNG("yellow-rose-3.png"),
+	}
+
+	// Initialize the animation encoder
+	width, height := 24, 24
+	anim, err := webp.NewAnimationEncoder(width, height, 0, 0)
+	if err != nil {
+		panic(err)
+	}
+	defer anim.Close()
+
+	// Add each frame to the animation
+	for i, im := range img {
+		// all frames of an animation must have the same dimensions
+		cropped := im.(interface {
+			SubImage(r image.Rectangle) image.Image
+		}).SubImage(image.Rect(0, 0, width, height))
+
+		if err := anim.AddFrame(cropped, 100*time.Millisecond); err != nil {
+			panic(err)
+		}
+	}
+
+	// Assemble the final animation
+	buf, err := anim.Assemble()
+	if err != nil {
+		panic(err)
+	}
+
+	// Write to disk
+	f := util.CreateFile("animation.webp")
+	defer f.Close()
+	f.Write(buf)
+}
+
+```
+
 ## TODO
 
 - Incremental decoding API
-- Container API (Animation)
+- Animation decoding
 
 ## License
 

webp/anim_encode.go

@@ -1,6 +1,8 @@
 package webp
 
 /*
+#cgo LDFLAGS: -lwebpmux
+
 #include <stdlib.h>
 #include <string.h>
 #include <webp/encode.h>

webp/anim_encode_test.go

@@ -0,0 +1,51 @@
+package webp_test
+
+import (
+	"image"
+	"testing"
+	"time"
+
+	"github.com/harukasan/go-libwebp/test/util"
+	"github.com/harukasan/go-libwebp/webp"
+)
+
+func TestEncodeAnimation(t *testing.T) {
+	data := util.ReadFile("cosmos.webp")
+	aWebP, err := webp.DecodeRGBA(data, &webp.DecoderOptions{})
+	if err != nil {
+		t.Fatalf("Got Error: %v", err)
+	}
+
+	img := []image.Image{
+		util.ReadPNG("butterfly.png"),
+		util.ReadPNG("checkerboard.png"),
+		util.ReadPNG("yellow-rose-3.png"),
+		aWebP,
+	}
+
+	width, height := 24, 24
+	anim, err := webp.NewAnimationEncoder(width, height, 0, 0)
+	if err != nil {
+		t.Fatalf("initializing decoder: %v", err)
+	}
+	defer anim.Close()
+
+	for i, im := range img {
+		// all frames of an animation must have the same dimensions
+		cropped := im.(interface {
+			SubImage(r image.Rectangle) image.Image
+		}).SubImage(image.Rect(0, 0, width, height))
+
+		if err := anim.AddFrame(cropped, 100*time.Millisecond); err != nil {
+			t.Errorf("adding frame %d: %v", i, err)
+		}
+	}
+
+	buf, err := anim.Assemble()
+	if err != nil {
+		t.Fatalf("assembling animation: %v", err)
+	}
+	if len(buf) == 0 {
+		t.Errorf("assembled animation is empty")
+	}
+}