Add RecordScreenAsGIF (#23)

ebitenutil/gif.go

@@ -0,0 +1,71 @@
+/*
+Copyright 2014 Hajime Hoshi
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package ebitenutil
+
+import (
+	"github.com/hajimehoshi/ebiten"
+	"image"
+	"image/color/palette"
+	"image/draw"
+	"image/gif"
+	"io"
+)
+
+type recorder struct {
+	inner        func(screen *ebiten.Image) error
+	writer       io.Writer
+	gif          *gif.GIF
+	currentFrame int
+}
+
+func (r *recorder) update(screen *ebiten.Image) error {
+	if err := r.inner(screen); err != nil {
+		return err
+	}
+	if r.currentFrame == len(r.gif.Image) {
+		return nil
+	}
+	img := image.NewPaletted(screen.Bounds(), palette.Plan9)
+	draw.Draw(img, img.Bounds(), screen, screen.Bounds().Min, draw.Over)
+	r.gif.Image[r.currentFrame] = img
+	// The actual FPS is 60, but GIF can't have such FPS. Set 50 FPS instead.
+	r.gif.Delay[r.currentFrame] = 2
+
+	r.currentFrame++
+	if r.currentFrame == len(r.gif.Image) {
+		if err := gif.EncodeAll(r.writer, r.gif); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// RecordScreenAsGIF returns updating function with recording the screen as an animation GIF image.
+//
+// This encodes each screen at each frame and may slows the application.
+func RecordScreenAsGIF(update func(*ebiten.Image) error, out io.Writer, frameNum int) func(*ebiten.Image) error {
+	r := &recorder{
+		inner:  update,
+		writer: out,
+		gif: &gif.GIF{
+			Image:     make([]*image.Paletted, frameNum),
+			Delay:     make([]int, frameNum),
+			LoopCount: -1,
+		},
+	}
+	return r.update
+}

example/alphablending/main.go

@@ -36,7 +36,7 @@ var (
 	saved           bool
 )
 
-func Update(screen *ebiten.Image) error {
+func update(screen *ebiten.Image) error {
 	count++
 	count %= 600
 	diff := float64(count) * 0.2
@@ -87,7 +87,10 @@ func main() {
 	if err != nil {
 		log.Fatal(err)
 	}
-	if err := ebiten.Run(Update, screenWidth, screenHeight, 2, "Alpha Blending (Ebiten Demo)"); err != nil {
+	update := update
+	// f, _ := os.Create("out.gif")
+	// update = ebitenutil.RecordScreenAsGIF(update, f, 100)
+	if err := ebiten.Run(update, screenWidth, screenHeight, 2, "Alpha Blending (Ebiten Demo)"); err != nil {
 		log.Fatal(err)
 	}
 }