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gif: fix local color map and coordinates

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R=nigeltao
CC=golang-dev
https://golang.org/cl/4759051
This commit is contained in:
Rob Pike 2011-07-19 11:47:15 +10:00
parent 7a18fc3bcb
commit a5a94f5d57
1 changed files with 19 additions and 14 deletions
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31
src/pkg/image/gif/reader.go
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@ -28,7 +28,9 @@ const (
fColorMapFollows = 1 << 7
// Image fields.
ifLocalColorTable = 1 << 7
ifInterlace = 1 << 6
ifPixelSizeMask = 7
// Graphic control flags.
gcTransparentColorSet = 1 << 0
@ -190,7 +192,9 @@ Loop:
}
// Undo the interlacing if necessary.
d.uninterlace(m)
if d.imageFields&ifInterlace != 0 {
uninterlace(m)
}
d.image = append(d.image, m)
d.delay = append(d.delay, d.delayTime)
@ -236,6 +240,9 @@ func (d *decoder) readColorMap() (image.PalettedColorModel, os.Error) {
return nil, fmt.Errorf("gif: can't handle %d bits per pixel", d.pixelSize)
}
numColors := 1 << d.pixelSize
if d.imageFields&ifLocalColorTable != 0 {
numColors = 1 << ((d.imageFields & ifPixelSizeMask) + 1)
}
numValues := 3 * numColors
_, err := io.ReadFull(d.r, d.tmp[0:numValues])
if err != nil {
@ -322,15 +329,15 @@ func (d *decoder) newImageFromDescriptor() (*image.Paletted, os.Error) {
if _, err := io.ReadFull(d.r, d.tmp[0:9]); err != nil {
return nil, fmt.Errorf("gif: can't read image descriptor: %s", err)
}
// TODO: This code (throughout) ignores the top and left values,
// and assumes (in interlacing, for example) that the images'
// widths and heights are all the same.
_ = int(d.tmp[0]) + int(d.tmp[1])<<8 // TODO: honor left value
_ = int(d.tmp[2]) + int(d.tmp[3])<<8 // TODO: honor top value
left := int(d.tmp[0]) + int(d.tmp[1])<<8
top := int(d.tmp[2]) + int(d.tmp[3])<<8
width := int(d.tmp[4]) + int(d.tmp[5])<<8
height := int(d.tmp[6]) + int(d.tmp[7])<<8
d.imageFields = d.tmp[8]
return image.NewPaletted(width, height, nil), nil
m := image.NewPaletted(width, height, nil)
// Overwrite the rectangle to take account of left and top.
m.Rect = image.Rect(left, top, left+width, top+height)
return m, nil
}
func (d *decoder) readBlock() (int, os.Error) {
@ -354,13 +361,11 @@ var interlacing = []interlaceScan{
{2, 1}, // Group 4 : Every 2nd. row, starting with row 1.
}
func (d *decoder) uninterlace(m *image.Paletted) {
if d.imageFields&ifInterlace == 0 {
return
}
// uninterlace rearranges the pixels in m to account for interlaced input.
func uninterlace(m *image.Paletted) {
var nPix []uint8
dx := d.width
dy := d.height
dx := m.Bounds().Dx()
dy := m.Bounds().Dy()
nPix = make([]uint8, dx*dy)
offset := 0 // steps through the input by sequential scan lines.
for _, pass := range interlacing {