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render: better handling of optimized GIFs #296

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merged 5 commits into from
Jul 6, 2022
Merged

render: better handling of optimized GIFs #296

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2ff9765
render: better handling of optimized GIFs
matslina Jun 10, 2022
18689ff
s/Point{0,0}/ZP/
matslina Jun 10, 2022
ea61aa9
s/Point{0,0}/ZP/
matslina Jun 10, 2022
4529df0
s/Point{0,0}/ZP/
matslina Jun 10, 2022
0aef614
update test
matslina Jun 10, 2022
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33 changes: 18 additions & 15 deletions render/image.go
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Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -71,15 +71,8 @@ func (p *Image) InitFromWebP(data []byte) error {
}

func (p *Image) InitFromGIF(data []byte) error {
// GIF support is quite limited and can't handle different
// positioned and sized frames, as well as disposal types.
//
// This means that many more optimized GIFs will not render
// correctly, with frame contents jumping around and previous
// frame contents always getting disposed, instead of kept.
//
// Unfortunatley the 'image/gif' package does not even expose
// frame positions, making it hard to implement these features.
// GIF support is a bit limited. Some optimized GIFs will not
// render correctly.
//
// Consider using WebP instead.
img, err := gif.DecodeAll(bytes.NewReader(data))
Expand All @@ -88,10 +81,20 @@ func (p *Image) InitFromGIF(data []byte) error {
}

p.Delay = img.Delay[0] * 10
for _, im := range img.Image {
imRGBA := image.NewRGBA(image.Rect(0, 0, im.Bounds().Dx(), im.Bounds().Dy()))
draw.Draw(imRGBA, imRGBA.Bounds(), im, image.Point{0, 0}, draw.Src)
p.imgs = append(p.imgs, imRGBA)

last := image.NewRGBA(image.Rect(0, 0, img.Image[0].Bounds().Dx(), img.Image[0].Bounds().Dy()))
draw.Draw(last, last.Bounds(), img.Image[0], image.ZP, draw.Src)

for _, src := range img.Image {

// Note: We're not really handling all disposal
// methods here, but this seems to be good enough.
draw.Draw(last, last.Bounds(), src, image.ZP, draw.Over)
frame := *last
frame.Pix = make([]uint8, len(last.Pix))
copy(frame.Pix, last.Pix)

p.imgs = append(p.imgs, &frame)
}

return nil
Expand Down Expand Up @@ -128,11 +131,11 @@ func (p *Image) Init() error {
nw, nh := p.Width, p.Height
if nw == 0 {
// scale width, maintaining original aspect ratio
nw = int(float64(nh)*(float64(w)/float64(h)))
nw = int(float64(nh) * (float64(w) / float64(h)))
}
if nh == 0 {
// scale height, maintaining original aspect ratio
nh = int(float64(nw)*(float64(h)/float64(w)))
nh = int(float64(nw) * (float64(h) / float64(w)))
}

for i := 0; i < len(p.imgs); i++ {
Expand Down
52 changes: 33 additions & 19 deletions render/image_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -12,9 +12,6 @@ import (
// plus sign on a transparent background.
const testPNG = "iVBORw0KGgoAAAANSUhEUgAAAAoAAAAMCAYAAABbayygAAAAOUlEQVQoU2P8z8Dwn4EIwAhSyMjAwIhPLVgNukKYDciaaawQl6dATkCxmmiFMF8PgGeICnAiYpABACrQO/WD80OVAAAAAElFTkSuQmCC"

// Animated GIF with a few pixels moving around
const testGIF = "R0lGODlhBQAEAPAAAAAAAAAAACH5BAF7AAAAIf8LTkVUU0NBUEUyLjADAQAAACwAAAAABQAEAAACBgRiaLmLBQAh+QQBewAAACwAAAAABQAEAAACBYRzpqhXACH5BAF7AAAALAAAAAAFAAQAAAIGDG6Qp8wFACH5BAF7AAAALAAAAAAFAAQAAAIGRIBnyMoFADs="

func TestImage(t *testing.T) {
raw, _ := base64.StdEncoding.DecodeString(testPNG)
img := &Image{Src: string(raw)}
Expand Down Expand Up @@ -108,6 +105,20 @@ func TestImageScaleAspectRatioHeight(t *testing.T) {
}

func TestImageAnimatedGif(t *testing.T) {
// Animated 5x4 GIF with 4 frames:
//
// frame 0: ..x..
// x....
// .x...
// ...x.
//
// Subsequent frames shift pixels right, overflowing into the
// next row.
//
// GIF has no disposal method set, and a delay of 1230 ms

const testGIF = "R0lGODlhBQAEAPAAAAAAAAAAACH5BAF7AAAAIf8LTkVUU0NBUEUyLjADAQAAACwAAAAABQAEAAACBgRiaLmLBQAh+QQBewAAACwAAAAABQAEAAACBYRzpqhXACH5BAF7AAAALAAAAAAFAAQAAAIGDG6Qp8wFACH5BAF7AAAALAAAAAAFAAQAAAIGRIBnyMoFADs="

raw, _ := base64.StdEncoding.DecodeString(testGIF)
img := &Image{Src: string(raw)}
img.Init()
Expand All @@ -127,23 +138,26 @@ func TestImageAnimatedGif(t *testing.T) {
".x...",
"...x.",
}, img.Paint(image.Rect(0, 0, 100, 100), 0)))

// since no disposal method is set, subsequent frames should
// draw on top of first frame
assert.Equal(t, nil, checkImage([]string{
"...x.",
".x...",
"..x..",
"....x",
"..xx.",
"xx...",
".xx..",
"...xx",
}, img.Paint(image.Rect(0, 0, 100, 100), 1)))
assert.Equal(t, nil, checkImage([]string{
"x...x",
"..x..",
"...x.",
".....",
"x.xxx",
"xxx..",
".xxx.",
"...xx",
}, img.Paint(image.Rect(0, 0, 100, 100), 2)))
assert.Equal(t, nil, checkImage([]string{
".x...",
"x..x.",
"....x",
".....",
"xxxxx",
"xxxx.",
".xxxx",
"...xx",
}, img.Paint(image.Rect(0, 0, 100, 100), 3)))

// loops after the last frame
Expand All @@ -154,9 +168,9 @@ func TestImageAnimatedGif(t *testing.T) {
"...x.",
}, img.Paint(image.Rect(0, 0, 100, 100), 4)))
assert.Equal(t, nil, checkImage([]string{
"...x.",
".x...",
"..x..",
"....x",
"..xx.",
"xx...",
".xx..",
"...xx",
}, img.Paint(image.Rect(0, 0, 100, 100), 5)))
}