how generating transparent GIF with golang using png images? - go

Question

I have a function that reads a lists of files and create a gif using each file on the list as a frame. But I have a problem. If my frames are png images with transparent background the output GIF have a black background.
I've read on the Internet that image.Paletted is related to the problem but I don't quite understand the issue.
func createAnimation(files []string, directory, filename string) {
outGif := &gif.GIF{}
for _, name := range files {
input := fmt.Sprintf("%s/%s", directory, name)
f, err := os.Open(input)
if err != nil {
log.Fatal(err)
}
imageData, _, err := image.Decode(f)
if err != nil {
log.Fatal(err)
}
buf := bytes.Buffer{}
if err = gif.Encode(&buf, imageData, nil); err != nil {
log.Fatal(err)
}
inGif, err := gif.Decode(&buf)
if err != nil {
log.Fatal(err)
}
f.Close()
outGif.Image = append(outGif.Image, inGif.(*image.Paletted))
outGif.Delay = append(outGif.Delay, 0)
}
output := fmt.Sprintf("FINAL_%s.gif", filename)
f, err := os.Create(output)
if err != nil {
log.Fatal(err)
}
gif.EncodeAll(f, outGif)
err = os.Rename(output, fmt.Sprintf("%s/%s", directory, output))
if err != nil {
log.Fatal(err)
}
}
Files is a slice of filenames e.g. {"base1.png", "base2.png"} and so on.
What should I check or modify in order to generate a transparent gif?

Answer 1

instead of encoding and decoding image you can use draw.Draw nethod. Just create a image.Paleted of size of the loaded image, specify palette you need (include transparent color) and perform draw call.
func Draw(dst Image, r image.Rectangle, src image.Image, sp image.Point, op Op)
// so
draw.Draw(newEmptyPalettedInage, loadedImage.Bounds(), loadedImage, loadedImage.Bounds().Min, 0)