[refactor] Make generation faster using .Pix

gif_progress.go

@@ -6,34 +6,35 @@ import (
 	"image/gif"
 )
 
+func clonePix(pix []uint8) []uint8 {
+	p := make([]uint8, len(pix))
+	copy(p, pix)
+	return p
+}
+
 func AddProgressBar(inOutGif *gif.GIF, barTop bool, barHeight int, barColor color.RGBA) {
 	// NOTE: inOutGif is changed destructively
 	width := inOutGif.Config.Width
 	height := inOutGif.Config.Height
 	imageLen := len(inOutGif.Image)
 	// Image size
 	imageSize := image.Rect(0, 0, width, height)
-	// Previous frame
-	previousImage := inOutGif.Image[0].SubImage(imageSize)
-	firstPalette := inOutGif.Image[0].Palette
+	// Previous pixels
+	previousPix := inOutGif.Image[0].Pix
 	for i, paletted := range inOutGif.Image {
 		// Create new empty paletted
-		newPaletted := image.NewPaletted(imageSize, firstPalette)
+		newPaletted := image.NewPaletted(imageSize, paletted.Palette)
 		// Copy previous frame to the new paletted
-		for x := 0; x < width; x++ {
-			for y := 0; y < height; y++ {
-				newPaletted.Set(x, y, previousImage.At(x, y))
-			}
-		}
-		// Copy whole image to the new paletted
+		newPaletted.Pix = previousPix
+		// Copy diff to the new paletted
 		rect := paletted.Rect
 		for x := rect.Min.X; x < rect.Max.X; x++ {
 			for y := rect.Min.Y; y < rect.Max.Y; y++ {
 				newPaletted.Set(x, y, paletted.At(x, y))
 			}
 		}
 		// Save as previous
-		previousImage = newPaletted.SubImage(imageSize)
+		previousPix = clonePix(newPaletted.Pix)
 
 		// Attach progress bar
 		w := int(float32(width) * ((float32(i)+1)/float32(imageLen)))