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Commit 20066679 authored by Nigel Tao's avatar Nigel Tao
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draw.Draw fast paths for the Over operator. 

Time (us) to draw a 200x200 src onto an image.RGBA dst with the Over
operator. Each case was measured three separate times, and the sorted
times are reported.

Fill case (where src is an image.ColorImage):
Before:
7438, 7511, 7526
After:
3073, 3087, 3102

Copy case (where src is an image.RGBA):
Before:
9506, 9510, 9563
After:
5262, 5300, 5344

R=rsc
CC=golang-dev
https://golang.org/cl/1532041
parent c2e9f0c5
Hide whitespace changes
Inline Side-by-side
Showing with 93 additions and 34 deletions
src/pkg/exp/draw/draw.go
View file @ 20066679
......@@ -12,6 +12,9 @@ package draw
import "image"
// m is the maximum color value returned by image.Color.RGBA.
const m = 1<<16 - 1
// A Porter-Duff compositing operator.
type Op int
......@@ -62,7 +65,20 @@ func DrawMask(dst Image, r Rectangle, src image.Image, sp Point, mask image.Imag
// Fast paths for special cases. If none of them apply, then we fall back to a general but slow implementation.
if dst0, ok := dst.(*image.RGBA); ok {
if op == Over {
if mask0, ok := mask.(*image.Alpha); ok {
if mask == nil {
if src0, ok := src.(image.ColorImage); ok {
drawFillOver(dst0, r, src0)
return
}
if src0, ok := src.(*image.RGBA); ok {
if dst0 == src0 && r.Overlaps(r.Add(sp.Sub(r.Min))) {
// TODO(nigeltao): Implement a fast path for the overlapping case.
} else {
drawCopyOver(dst0, r, src0, sp)
return
}
}
} else if mask0, ok := mask.(*image.Alpha); ok {
if src0, ok := src.(image.ColorImage); ok {
drawGlyphOver(dst0, r, src0, mask0, mp)
return
......@@ -71,14 +87,14 @@ func DrawMask(dst Image, r Rectangle, src image.Image, sp Point, mask image.Imag
} else {
if mask == nil {
if src0, ok := src.(image.ColorImage); ok {
drawFill(dst0, r, src0)
drawFillSrc(dst0, r, src0)
return
}
if src0, ok := src.(*image.RGBA); ok {
if dst0 == src0 && r.Overlaps(r.Add(sp.Sub(r.Min))) {
// TODO(nigeltao): Implement a fast path for the overlapping case.
} else {
drawCopy(dst0, r, src0, sp)
drawCopySrc(dst0, r, src0, sp)
return
}
}
......@@ -105,8 +121,7 @@ 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 {
const M = 1<<16 - 1
ma := uint32(M)
ma := uint32(m)
if mask != nil {
_, _, _, ma = mask.At(mx, my).RGBA()
}
......@@ -117,7 +132,7 @@ func DrawMask(dst Image, r Rectangle, src image.Image, sp Point, mask image.Imag
} else {
dst.Set(x, y, zeroColor)
}
case ma == M && op == Src:
case ma == m && op == Src:
dst.Set(x, y, src.At(sx, sy))
default:
sr, sg, sb, sa := src.At(sx, sy).RGBA()
......@@ -126,16 +141,16 @@ func DrawMask(dst Image, r Rectangle, src image.Image, sp Point, mask image.Imag
}
if op == Over {
dr, dg, db, da := dst.At(x, y).RGBA()
a := M - (sa * ma / M)
out.R = uint16((dr*a + sr*ma) / M)
out.G = uint16((dg*a + sg*ma) / M)
out.B = uint16((db*a + sb*ma) / M)
out.A = uint16((da*a + sa*ma) / M)
a := m - (sa * ma / m)
out.R = uint16((dr*a + sr*ma) / m)
out.G = uint16((dg*a + sg*ma) / m)
out.B = uint16((db*a + sb*ma) / m)
out.A = uint16((da*a + sa*ma) / m)
} else {
out.R = uint16(sr * ma / M)
out.G = uint16(sg * ma / M)
out.B = uint16(sb * ma / M)
out.A = uint16(sa * ma / M)
out.R = uint16(sr * ma / m)
out.G = uint16(sg * ma / m)
out.B = uint16(sb * ma / m)
out.A = uint16(sa * ma / m)
}
dst.Set(x, y, out)
}
......@@ -143,6 +158,52 @@ func DrawMask(dst Image, r Rectangle, src image.Image, sp Point, mask image.Imag
}
}
func drawFillOver(dst *image.RGBA, r Rectangle, src image.ColorImage) {
cr, cg, cb, ca := src.RGBA()
// The 0x101 is here for the same reason as in drawRGBA.
a := (m - ca) * 0x101
x0, x1 := r.Min.X, r.Max.X
y0, y1 := r.Min.Y, r.Max.Y
for y := y0; y != y1; y++ {
p := dst.Pixel[y]
for x := x0; x != x1; x++ {
rgba := p[x]
dr := (uint32(rgba.R)*a)/m + cr
dg := (uint32(rgba.G)*a)/m + cg
db := (uint32(rgba.B)*a)/m + cb
da := (uint32(rgba.A)*a)/m + ca
p[x] = image.RGBAColor{uint8(dr >> 8), uint8(dg >> 8), uint8(db >> 8), uint8(da >> 8)}
}
}
}
func drawCopyOver(dst *image.RGBA, r Rectangle, src *image.RGBA, sp Point) {
x0, x1 := r.Min.X, r.Max.X
y0, y1 := r.Min.Y, r.Max.Y
for y, sy := y0, sp.Y; y != y1; y, sy = y+1, sy+1 {
dpix := dst.Pixel[y]
spix := src.Pixel[y]
for x, sx := x0, sp.X; x != x1; x, sx = x+1, sx+1 {
// For unknown reasons, even though both dpix[x] and spix[sx] are
// image.RGBAColors, on an x86 CPU it seems fastest to call RGBA
// for the source but to do it manually for the destination.
sr, sg, sb, sa := spix[sx].RGBA()
drgba := dpix[x]
dr := uint32(drgba.R)
dg := uint32(drgba.G)
db := uint32(drgba.B)
da := uint32(drgba.A)
// The 0x101 is here for the same reason as in drawRGBA.
a := (m - sa) * 0x101
dr = (dr*a)/m + sr
dg = (dg*a)/m + sg
db = (db*a)/m + sb
da = (da*a)/m + sa
dpix[x] = image.RGBAColor{uint8(dr >> 8), uint8(dg >> 8), uint8(db >> 8), uint8(da >> 8)}
}
}
}
func drawGlyphOver(dst *image.RGBA, r Rectangle, src image.ColorImage, mask *image.Alpha, mp Point) {
x0, x1 := r.Min.X, r.Max.X
y0, y1 := r.Min.Y, r.Max.Y
......@@ -160,19 +221,18 @@ func drawGlyphOver(dst *image.RGBA, r Rectangle, src image.ColorImage, mask *ima
dg := uint32(rgba.G)
db := uint32(rgba.B)
da := uint32(rgba.A)
const M = 1<<16 - 1
// The 0x101 is here for the same reason as in drawRGBA.
a := (M - (ca * ma / M)) * 0x101
dr = (dr*a + cr*ma) / M
dg = (dg*a + cg*ma) / M
db = (db*a + cb*ma) / M
da = (da*a + ca*ma) / M
a := (m - (ca * ma / m)) * 0x101
dr = (dr*a + cr*ma) / m
dg = (dg*a + cg*ma) / m
db = (db*a + cb*ma) / m
da = (da*a + ca*ma) / m
p[x] = image.RGBAColor{uint8(dr >> 8), uint8(dg >> 8), uint8(db >> 8), uint8(da >> 8)}
}
}
}
func drawFill(dst *image.RGBA, r Rectangle, src image.ColorImage) {
func drawFillSrc(dst *image.RGBA, r Rectangle, src image.ColorImage) {
if r.Dy() < 1 {
return
}
......@@ -193,7 +253,7 @@ func drawFill(dst *image.RGBA, r Rectangle, src image.ColorImage) {
}
}
func drawCopy(dst *image.RGBA, r Rectangle, src *image.RGBA, sp Point) {
func drawCopySrc(dst *image.RGBA, r Rectangle, src *image.RGBA, sp Point) {
dx0, dx1 := r.Min.X, r.Max.X
dy0, dy1 := r.Min.Y, r.Max.Y
sx0, sx1 := sp.X, sp.X+dx1-dx0
......@@ -219,8 +279,7 @@ func drawRGBA(dst *image.RGBA, r Rectangle, src image.Image, sp Point, mask imag
mx := mp.X + x0 - r.Min.X
p := dst.Pixel[y]
for x := x0; x != x1; x, sx, mx = x+dx, sx+dx, mx+dx {
const M = 1<<16 - 1
ma := uint32(M)
ma := uint32(m)
if mask != nil {
_, _, _, ma = mask.At(mx, my).RGBA()
}
......@@ -238,16 +297,16 @@ func drawRGBA(dst *image.RGBA, r Rectangle, src image.Image, sp Point, mask imag
// and similarly for dg, db and da, but instead we multiply a
// (which is a 16-bit color, ranging in [0,65535]) by 0x101.
// This yields the same result, but is fewer arithmetic operations.
a := (M - (sa * ma / M)) * 0x101
dr = (dr*a + sr*ma) / M
dg = (dg*a + sg*ma) / M
db = (db*a + sb*ma) / M
da = (da*a + sa*ma) / M
a := (m - (sa * ma / m)) * 0x101
dr = (dr*a + sr*ma) / m
dg = (dg*a + sg*ma) / m
db = (db*a + sb*ma) / m
da = (da*a + sa*ma) / m
} else {
dr = sr * ma / M
dg = sg * ma / M
db = sb * ma / M
da = sa * ma / M
dr = sr * ma / m
dg = sg * ma / m
db = sb * ma / m
da = sa * ma / m
}
p[x] = image.RGBAColor{uint8(dr >> 8), uint8(dg >> 8), uint8(db >> 8), uint8(da >> 8)}
}
......
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