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
// 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
} 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
}
}
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()
}
} 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()
}
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)
}
}
}
+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
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
}
}
}
-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
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()
}
// 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)}
}