Revert "ebitenutil: Remove RecordScreenAsGIF implementation (#500)"

This reverts commit e3b99dd081.

This is for backward compatibility

ebitenutil/gif.go

@@ -15,12 +15,126 @@
 package ebitenutil
 
 import (
+	"image"
+	"image/color"
+	"image/color/palette"
+	"image/draw"
+	"image/gif"
 	"io"
+	"sync"
 
 	"github.com/hajimehoshi/ebiten"
 )
 
-// RecordScreenAsGIF is deprecated as of version 1.6.0-alpha.
-func RecordScreenAsGIF(update func(*ebiten.Image) error, out io.Writer, frameNum int) func(*ebiten.Image) error {
-	panic("ebitenutil: RecordScreenAsGIF is no longer implemented")
+type recorder struct {
+	inner        func(screen *ebiten.Image) error
+	writer       io.Writer
+	frameNum     int
+	skips        int
+	gif          *gif.GIF
+	currentFrame int
+	wg           sync.WaitGroup
+}
+
+var cheapPalette color.Palette
+
+func init() {
+	cs := []color.Color{}
+	for _, r := range []uint8{0x00, 0x80, 0xff} {
+		for _, g := range []uint8{0x00, 0x80, 0xff} {
+			for _, b := range []uint8{0x00, 0x80, 0xff} {
+				cs = append(cs, color.RGBA{r, g, b, 0xff})
+			}
+		}
+	}
+	cheapPalette = color.Palette(cs)
+}
+
+func (r *recorder) delay() int {
+	delay := 100 * r.skips / ebiten.FPS
+	if delay < 2 {
+		return 2
+	}
+	return delay
+}
+
+func (r *recorder) palette() color.Palette {
+	if 1 < (r.frameNum-1)/r.skips+1 {
+		return cheapPalette
+	}
+	return palette.Plan9
+}
+
+func (r *recorder) update(screen *ebiten.Image) error {
+	if err := r.inner(screen); err != nil {
+		return err
+	}
+	if r.currentFrame == r.frameNum {
+		return nil
+	}
+	if r.currentFrame%r.skips == 0 {
+		if r.gif == nil {
+			num := (r.frameNum-1)/r.skips + 1
+			r.gif = &gif.GIF{
+				Image:     make([]*image.Paletted, num),
+				Delay:     make([]int, num),
+				LoopCount: -1,
+			}
+		}
+		s := image.NewNRGBA(screen.Bounds())
+		draw.Draw(s, s.Bounds(), screen, screen.Bounds().Min, draw.Src)
+
+		img := image.NewPaletted(s.Bounds(), r.palette())
+		f := r.currentFrame / r.skips
+		r.wg.Add(1)
+		go func() {
+			defer r.wg.Done()
+			draw.FloydSteinberg.Draw(img, img.Bounds(), s, s.Bounds().Min)
+			r.gif.Image[f] = img
+			r.gif.Delay[f] = r.delay()
+		}()
+	}
+
+	r.currentFrame++
+	if r.currentFrame == r.frameNum {
+		r.wg.Wait()
+		if err := gif.EncodeAll(r.writer, r.gif); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// RecordScreenAsGIF is deprecated as of version 1.6.0-alpha.
+//
+// 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.
+//
+// Here is the example to record initial 120 frames of your game:
+//
+//     func update(screen *ebiten.Image) error {
+//         // ...
+//     }
+//
+//     func main() {
+//         out, err := os.Create("output.gif")
+//         if err != nil {
+//             log.Fatal(err)
+//         }
+//         defer out.Close()
+//
+//         update := RecordScreenAsGIF(update, out, 120)
+//         if err := ebiten.Run(update, 320, 240, 2, "Your game's title"); err != nil {
+//             log.Fatal(err)
+//         }
+//     }
+func RecordScreenAsGIF(update func(*ebiten.Image) error, out io.Writer, frameNum int) func(*ebiten.Image) error {
+	r := &recorder{
+		inner:    update,
+		writer:   out,
+		frameNum: frameNum,
+		skips:    10,
+	}
+	return r.update
 }

ebitenutil/import.go

@@ -17,5 +17,6 @@ package ebitenutil
 import (
 	// Import image/png for backward compatibility (#500, #516)
 	// TODO: Deprecate and remove this at the next major version (2.0).
+	_ "image/gif"
 	_ "image/png"
 )