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image: add PalettedImage interface, and make image/png recognize it.

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R=golang-dev, rsc, bradfitz, nigeltao
CC=golang-dev
https://golang.org/cl/4956046
This commit is contained in:
Jaroslavas Počepko 2011-08-31 08:27:00 +10:00 committed by Nigel Tao
parent e1cfb6f3a9
commit 68a04dce93
2 changed files with 32 additions and 6 deletions
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14
src/pkg/image/image.go
View File

@ -24,6 +24,17 @@ type Image interface {
At(x, y int) Color
}
// PalettedImage is an image whose colors may come from a limited palette.
// If m is a PalettedImage and m.ColorModel() returns a PalettedColorModel p,
// then m.At(x, y) should be equivalent to p[m.ColorIndexAt(x, y)]. If m's
// color model is not a PalettedColorModel, then ColorIndexAt's behavior is
// undefined.
type PalettedImage interface {
// ColorIndexAt returns the palette index of the pixel at (x, y).
ColorIndexAt(x, y int) uint8
Image
}
// RGBA is an in-memory image of RGBAColor values.
type RGBA struct {
// Pix holds the image's pixels, in R, G, B, A order. The pixel at
@ -741,6 +752,9 @@ func (p PalettedColorModel) Index(c Color) int {
dr, dg, db := diff(cr, vr), diff(cg, vg), diff(cb, vb)
ssd := (dr * dr) + (dg * dg) + (db * db)
if ssd < bestSSD {
if ssd == 0 {
return i
}
ret, bestSSD = i, ssd
}
}

24
src/pkg/image/png/writer.go
View File

@ -336,9 +336,16 @@ func writeImage(w io.Writer, m image.Image, cb int) os.Error {
}
}
case cbP8:
paletted := m.(*image.Paletted)
offset := (y - b.Min.Y) * paletted.Stride
copy(cr[0][1:], paletted.Pix[offset:offset+b.Dx()])
if p, _ := m.(*image.Paletted); p != nil {
offset := (y - b.Min.Y) * p.Stride
copy(cr[0][1:], p.Pix[offset:offset+b.Dx()])
} else {
pi := m.(image.PalettedImage)
for x := b.Min.X; x < b.Max.X; x++ {
cr[0][i] = pi.ColorIndexAt(x, y)
i += 1
}
}
case cbTCA8:
// Convert from image.Image (which is alpha-premultiplied) to PNG's non-alpha-premultiplied.
for x := b.Min.X; x < b.Max.X; x++ {
@ -432,7 +439,12 @@ func Encode(w io.Writer, m image.Image) os.Error {
var e encoder
e.w = w
e.m = m
pal, _ := m.(*image.Paletted)
var pal image.PalettedColorModel
// cbP8 encoding needs PalettedImage's ColorIndexAt method.
if _, ok := m.(image.PalettedImage); ok {
pal, _ = m.ColorModel().(image.PalettedColorModel)
}
if pal != nil {
e.cb = cbP8
} else {
@ -459,8 +471,8 @@ func Encode(w io.Writer, m image.Image) os.Error {
_, e.err = io.WriteString(w, pngHeader)
e.writeIHDR()
if pal != nil {
e.writePLTE(pal.Palette)
e.maybeWritetRNS(pal.Palette)
e.writePLTE(pal)
e.maybeWritetRNS(pal)
}
e.writeIDATs()
e.writeIEND()