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Commit 2bb59fd7 authored by Nigel Tao's avatar Nigel Tao
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Make image.Color.RGBA return 16 bit color instead of 32 bit color. 

R=rsc
CC=golang-dev
https://golang.org/cl/1388041
parent d5a8647d
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Inline Side-by-side
Showing with 41 additions and 108 deletions
src/pkg/exp/draw/color.go
View file @ 2bb59fd7
......@@ -51,13 +51,9 @@ func (c Color) RGBA() (r, g, b, a uint32) {
x := uint32(c)
r, g, b, a = x>>24, (x>>16)&0xFF, (x>>8)&0xFF, x&0xFF
r |= r << 8
r |= r << 16
g |= g << 8
g |= g << 16
b |= b << 8
b |= b << 16
a |= a << 8
a |= a << 16
return
}
......@@ -103,7 +99,7 @@ func toColor(color image.Color) image.Color {
return c
}
r, g, b, a := color.RGBA()
return Color(r>>24<<24 | g>>24<<16 | b>>24<<8 | a>>24)
return Color(r>>8<<24 | g>>8<<16 | b>>8<<8 | a>>8)
}
func (c Color) ColorModel() image.ColorModel { return image.ColorModelFunc(toColor) }
src/pkg/exp/draw/draw.go
View file @ 2bb59fd7
......@@ -105,13 +105,10 @@ func DrawMask(dst Image, r Rectangle, src image.Image, sp Point, mask image.Imag
sx := sp.X + x0 - r.Min.X
mx := mp.X + x0 - r.Min.X
for x := x0; x != x1; x, sx, mx = x+dx, sx+dx, mx+dx {
// A nil mask is equivalent to a fully opaque, infinitely large mask.
// We work in 16-bit color, so that multiplying two values does not overflow a uint32.
const M = 1<<16 - 1
ma := uint32(M)
if mask != nil {
_, _, _, ma = mask.At(mx, my).RGBA()
ma >>= 16
}
switch {
case ma == 0:
......@@ -124,19 +121,11 @@ func DrawMask(dst Image, r Rectangle, src image.Image, sp Point, mask image.Imag
dst.Set(x, y, src.At(sx, sy))
default:
sr, sg, sb, sa := src.At(sx, sy).RGBA()
sr >>= 16
sg >>= 16
sb >>= 16
sa >>= 16
if out == nil {
out = new(image.RGBA64Color)
}
if op == Over {
dr, dg, db, da := dst.At(x, y).RGBA()
dr >>= 16
dg >>= 16
db >>= 16
da >>= 16
a := M - (sa * ma / M)
out.R = uint16((dr*a + sr*ma) / M)
out.G = uint16((dg*a + sg*ma) / M)
......@@ -158,10 +147,6 @@ func drawGlyphOver(dst *image.RGBA, r Rectangle, src image.ColorImage, mask *ima
x0, x1 := r.Min.X, r.Max.X
y0, y1 := r.Min.Y, r.Max.Y
cr, cg, cb, ca := src.RGBA()
cr >>= 16
cg >>= 16
cb >>= 16
ca >>= 16
for y, my := y0, mp.Y; y != y1; y, my = y+1, my+1 {
p := dst.Pixel[y]
for x, mx := x0, mp.X; x != x1; x, mx = x+1, mx+1 {
......@@ -192,7 +177,7 @@ func drawFill(dst *image.RGBA, r Rectangle, src image.ColorImage) {
return
}
cr, cg, cb, ca := src.RGBA()
color := image.RGBAColor{uint8(cr >> 24), uint8(cg >> 24), uint8(cb >> 24), uint8(ca >> 24)}
color := image.RGBAColor{uint8(cr >> 8), uint8(cg >> 8), uint8(cb >> 8), uint8(ca >> 8)}
// The built-in copy function is faster than a straightforward for loop to fill the destination with
// the color, but copy requires a slice source. We therefore use a for loop to fill the first row, and
// then use the first row as the slice source for the remaining rows.
......@@ -238,13 +223,8 @@ func drawRGBA(dst *image.RGBA, r Rectangle, src image.Image, sp Point, mask imag
ma := uint32(M)
if mask != nil {
_, _, _, ma = mask.At(mx, my).RGBA()
ma >>= 16
}
sr, sg, sb, sa := src.At(sx, sy).RGBA()
sr >>= 16
sg >>= 16
sb >>= 16
sa >>= 16
var dr, dg, db, da uint32
if op == Over {
rgba := p[x]
......
src/pkg/exp/draw/draw_test.go
View file @ 2bb59fd7
......@@ -106,20 +106,11 @@ func makeGolden(dst image.Image, t drawTest) image.Image {
var dr, dg, db, da uint32
if t.op == Over {
dr, dg, db, da = dst.At(x, y).RGBA()
dr >>= 16
dg >>= 16
db >>= 16
da >>= 16
}
sr, sg, sb, sa := t.src.At(sx, sy).RGBA()
sr >>= 16
sg >>= 16
sb >>= 16
sa >>= 16
ma := uint32(M)
if t.mask != nil {
_, _, _, ma = t.mask.At(mx, my).RGBA()
ma >>= 16
}
a := M - (sa * ma / M)
golden.Set(x, y, image.RGBA64Color{
......
src/pkg/exp/nacl/av/image.go
View file @ 2bb59fd7
......@@ -61,16 +61,12 @@ func (p Color) RGBA() (r, g, b, a uint32) {
x := uint32(p)
a = x >> 24
a |= a << 8
a |= a << 16
r = (x >> 16) & 0xFF
r |= r << 8
r |= r << 16
g = (x >> 8) & 0xFF
g |= g << 8
g |= g << 16
b = x & 0xFF
b |= b << 8
b |= b << 16
return
}
......
src/pkg/image/color.go
View file @ 2bb59fd7
......@@ -4,14 +4,15 @@
package image
// TODO(nigeltao): Think about how floating-point color models work.
// All Colors can convert themselves, with a possible loss of precision, to 128-bit alpha-premultiplied RGBA.
// All Colors can convert themselves, with a possible loss of precision,
// to 64-bit alpha-premultiplied RGBA. Each channel value ranges within
// [0, 0xFFFF].
type Color interface {
RGBA() (r, g, b, a uint32)
}
// An RGBAColor represents a traditional 32-bit alpha-premultiplied color, having 8 bits for each of red, green, blue and alpha.
// An RGBAColor represents a traditional 32-bit alpha-premultiplied color,
// having 8 bits for each of red, green, blue and alpha.
type RGBAColor struct {
R, G, B, A uint8
}
......@@ -19,34 +20,23 @@ type RGBAColor struct {
func (c RGBAColor) RGBA() (r, g, b, a uint32) {
r = uint32(c.R)
r |= r << 8
r |= r << 16
g = uint32(c.G)
g |= g << 8
g |= g << 16
b = uint32(c.B)
b |= b << 8
b |= b << 16
a = uint32(c.A)
a |= a << 8
a |= a << 16
return
}
// An RGBA64Color represents a 64-bit alpha-premultiplied color, having 16 bits for each of red, green, blue and alpha.
// An RGBA64Color represents a 64-bit alpha-premultiplied color,
// having 16 bits for each of red, green, blue and alpha.
type RGBA64Color struct {
R, G, B, A uint16
}
func (c RGBA64Color) RGBA() (r, g, b, a uint32) {
r = uint32(c.R)
r |= r << 16
g = uint32(c.G)
g |= g << 16
b = uint32(c.B)
b |= b << 16
a = uint32(c.A)
a |= a << 16
return
return uint32(c.R), uint32(c.G), uint32(c.B), uint32(c.A)
}
// An NRGBAColor represents a non-alpha-premultiplied 32-bit color.
......@@ -59,24 +49,21 @@ func (c NRGBAColor) RGBA() (r, g, b, a uint32) {
r |= r << 8
r *= uint32(c.A)
r /= 0xff
r |= r << 16
g = uint32(c.G)
g |= g << 8
g *= uint32(c.A)
g /= 0xff
g |= g << 16
b = uint32(c.B)
b |= b << 8
b *= uint32(c.A)
b /= 0xff
b |= b << 16
a = uint32(c.A)
a |= a << 8
a |= a << 16
return
}
// An NRGBA64Color represents a non-alpha-premultiplied 64-bit color, having 16 bits for each of red, green, blue and alpha.
// An NRGBA64Color represents a non-alpha-premultiplied 64-bit color,
// having 16 bits for each of red, green, blue and alpha.
type NRGBA64Color struct {
R, G, B, A uint16
}
......@@ -85,18 +72,13 @@ func (c NRGBA64Color) RGBA() (r, g, b, a uint32) {
r = uint32(c.R)
r *= uint32(c.A)
r /= 0xffff
r |= r << 16
g = uint32(c.G)
g *= uint32(c.A)
g /= 0xffff
g |= g << 16
b = uint32(c.B)
b *= uint32(c.A)
b /= 0xffff
b |= b << 16
a = uint32(c.A)
a |= a << 8
a |= a << 16
return
}
......@@ -108,12 +90,11 @@ type AlphaColor struct {
func (c AlphaColor) RGBA() (r, g, b, a uint32) {
a = uint32(c.A)
a |= a << 8
a |= a << 16
return a, a, a, a
}
// A ColorModel can convert foreign Colors, with a possible loss of precision, to a Color
// from its own color model.
// A ColorModel can convert foreign Colors, with a possible loss of precision,
// to a Color from its own color model.
type ColorModel interface {
Convert(c Color) Color
}
......@@ -129,36 +110,32 @@ func (f ColorModelFunc) Convert(c Color) Color {
}
func toRGBAColor(c Color) Color {
if _, ok := c.(RGBAColor); ok { // no-op conversion
if _, ok := c.(RGBAColor); ok {
return c
}
r, g, b, a := c.RGBA()
return RGBAColor{uint8(r >> 24), uint8(g >> 24), uint8(b >> 24), uint8(a >> 24)}
return RGBAColor{uint8(r >> 8), uint8(g >> 8), uint8(b >> 8), uint8(a >> 8)}
}
func toRGBA64Color(c Color) Color {
if _, ok := c.(RGBA64Color); ok { // no-op conversion
if _, ok := c.(RGBA64Color); ok {
return c
}
r, g, b, a := c.RGBA()
return RGBA64Color{uint16(r >> 16), uint16(g >> 16), uint16(b >> 16), uint16(a >> 16)}
return RGBA64Color{uint16(r), uint16(g), uint16(b), uint16(a)}
}
func toNRGBAColor(c Color) Color {
if _, ok := c.(NRGBAColor); ok { // no-op conversion
if _, ok := c.(NRGBAColor); ok {
return c
}
r, g, b, a := c.RGBA()
a >>= 16
if a == 0xffff {
return NRGBAColor{uint8(r >> 24), uint8(g >> 24), uint8(b >> 24), 0xff}
return NRGBAColor{uint8(r >> 8), uint8(g >> 8), uint8(b >> 8), 0xff}
}
if a == 0 {
return NRGBAColor{0, 0, 0, 0}
}
r >>= 16
g >>= 16
b >>= 16
// Since Color.RGBA returns a alpha-premultiplied color, we should have r <= a && g <= a && b <= a.
r = (r * 0xffff) / a
g = (g * 0xffff) / a
......@@ -167,14 +144,10 @@ func toNRGBAColor(c Color) Color {
}
func toNRGBA64Color(c Color) Color {
if _, ok := c.(NRGBA64Color); ok { // no-op conversion
if _, ok := c.(NRGBA64Color); ok {
return c
}
r, g, b, a := c.RGBA()
a >>= 16
r >>= 16
g >>= 16
b >>= 16
if a == 0xffff {
return NRGBA64Color{uint16(r), uint16(g), uint16(b), 0xffff}
}
......@@ -189,11 +162,11 @@ func toNRGBA64Color(c Color) Color {
}
func toAlphaColor(c Color) Color {
if _, ok := c.(AlphaColor); ok { // no-op conversion
if _, ok := c.(AlphaColor); ok {
return c
}
_, _, _, a := c.RGBA()
return AlphaColor{uint8(a >> 24)}
return AlphaColor{uint8(a >> 8)}
}
// The ColorModel associated with RGBAColor.
......
src/pkg/image/image.go
View file @ 2bb59fd7
......@@ -185,21 +185,18 @@ func (p PalettedColorModel) Convert(c Color) Color {
if len(p) == 0 {
return nil
}
// TODO(nigeltao): Revisit the "pick the palette color which minimizes sum-squared-difference"
// algorithm when the premultiplied vs unpremultiplied issue is resolved.
// Currently, we only compare the R, G and B values, and ignore A.
cr, cg, cb, _ := c.RGBA()
// Shift by 17 bits to avoid potential uint32 overflow in sum-squared-difference.
cr >>= 17
cg >>= 17
cb >>= 17
// Shift by 1 bit to avoid potential uint32 overflow in sum-squared-difference.
cr >>= 1
cg >>= 1
cb >>= 1
result := Color(nil)
bestSSD := uint32(1<<32 - 1)
for _, v := range p {
vr, vg, vb, _ := v.RGBA()
vr >>= 17
vg >>= 17
vb >>= 17
vr >>= 1
vg >>= 1
vb >>= 1
dr, dg, db := diff(cr, vr), diff(cg, vg), diff(cb, vb)
ssd := (dr * dr) + (dg * dg) + (db * db)
if ssd < bestSSD {
......
src/pkg/image/png/reader_test.go
View file @ 2bb59fd7
......@@ -76,9 +76,9 @@ func sng(w io.WriteCloser, filename string, png image.Image) {
io.WriteString(w, "PLTE {\n")
for i := 0; i < len(cpm); i++ {
r, g, b, _ := cpm[i].RGBA()
r >>= 24
g >>= 24
b >>= 24
r >>= 8
g >>= 8
b >>= 8
fmt.Fprintf(w, " (%3d,%3d,%3d) # rgb = (0x%02x,0x%02x,0x%02x)\n", r, g, b, r, g, b)
}
io.WriteString(w, "}\n")
......
src/pkg/image/png/writer.go
View file @ 2bb59fd7
......@@ -37,7 +37,7 @@ func opaque(m image.Image) bool {
for y := 0; y < m.Height(); y++ {
for x := 0; x < m.Width(); x++ {
_, _, _, a := m.At(x, y).RGBA()
if a != 0xffffffff {
if a != 0xffff {
return false
}
}
......@@ -101,13 +101,13 @@ func (e *encoder) writePLTE(p image.PalettedColorModel) {
}
for i := 0; i < len(p); i++ {
r, g, b, a := p[i].RGBA()
if a != 0xffffffff {
if a != 0xffff {
e.err = UnsupportedError("non-opaque palette color")
return
}
e.tmp[3*i+0] = uint8(r >> 24)
e.tmp[3*i+1] = uint8(g >> 24)
e.tmp[3*i+2] = uint8(b >> 24)
e.tmp[3*i+0] = uint8(r >> 8)
e.tmp[3*i+1] = uint8(g >> 8)
e.tmp[3*i+2] = uint8(b >> 8)
}
e.writeChunk(e.tmp[0:3*len(p)], "PLTE")
}
......@@ -261,9 +261,9 @@ func writeImage(w io.Writer, m image.Image, ct uint8) os.Error {
for x := 0; x < m.Width(); x++ {
// We have previously verified that the alpha value is fully opaque.
r, g, b, _ := m.At(x, y).RGBA()
cr[0][3*x+1] = uint8(r >> 24)
cr[0][3*x+2] = uint8(g >> 24)
cr[0][3*x+3] = uint8(b >> 24)
cr[0][3*x+1] = uint8(r >> 8)
cr[0][3*x+2] = uint8(g >> 8)
cr[0][3*x+3] = uint8(b >> 8)
}
case ctPaletted:
for x := 0; x < m.Width(); x++ {
......
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