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Diffstat (limited to 'libgo/go/image/draw/draw.go')
-rw-r--r--libgo/go/image/draw/draw.go209
1 files changed, 190 insertions, 19 deletions
diff --git a/libgo/go/image/draw/draw.go b/libgo/go/image/draw/draw.go
index 56d30dd6f82..661230e7c59 100644
--- a/libgo/go/image/draw/draw.go
+++ b/libgo/go/image/draw/draw.go
@@ -16,6 +16,19 @@ import (
// m is the maximum color value returned by image.Color.RGBA.
const m = 1<<16 - 1
+// Image is an image.Image with a Set method to change a single pixel.
+type Image interface {
+ image.Image
+ Set(x, y int, c color.Color)
+}
+
+// Quantizer produces a palette for an image.
+type Quantizer interface {
+ // Quantize appends up to cap(p) - len(p) colors to p and returns the
+ // updated palette suitable for converting m to a paletted image.
+ Quantize(p color.Palette, m image.Image) color.Palette
+}
+
// Op is a Porter-Duff compositing operator.
type Op int
@@ -26,15 +39,31 @@ const (
Src
)
-// A draw.Image is an image.Image with a Set method to change a single pixel.
-type Image interface {
- image.Image
- Set(x, y int, c color.Color)
+// Draw implements the Drawer interface by calling the Draw function with this
+// Op.
+func (op Op) Draw(dst Image, r image.Rectangle, src image.Image, sp image.Point) {
+ DrawMask(dst, r, src, sp, nil, image.Point{}, op)
}
-// Draw calls DrawMask with a nil mask.
-func Draw(dst Image, r image.Rectangle, src image.Image, sp image.Point, op Op) {
- DrawMask(dst, r, src, sp, nil, image.ZP, op)
+// Drawer contains the Draw method.
+type Drawer interface {
+ // Draw aligns r.Min in dst with sp in src and then replaces the
+ // rectangle r in dst with the result of drawing src on dst.
+ Draw(dst Image, r image.Rectangle, src image.Image, sp image.Point)
+}
+
+// FloydSteinberg is a Drawer that is the Src Op with Floyd-Steinberg error
+// diffusion.
+var FloydSteinberg Drawer = floydSteinberg{}
+
+type floydSteinberg struct{}
+
+func (floydSteinberg) Draw(dst Image, r image.Rectangle, src image.Image, sp image.Point) {
+ clip(dst, &r, src, &sp, nil, nil)
+ if r.Empty() {
+ return
+ }
+ drawPaletted(dst, r, src, sp, true)
}
// clip clips r against each image's bounds (after translating into the
@@ -58,6 +87,17 @@ func clip(dst Image, r *image.Rectangle, src image.Image, sp *image.Point, mask
(*mp).Y += dy
}
+func processBackward(dst Image, r image.Rectangle, src image.Image, sp image.Point) bool {
+ return image.Image(dst) == src &&
+ r.Overlaps(r.Add(sp.Sub(r.Min))) &&
+ (sp.Y < r.Min.Y || (sp.Y == r.Min.Y && sp.X < r.Min.X))
+}
+
+// Draw calls DrawMask with a nil mask.
+func Draw(dst Image, r image.Rectangle, src image.Image, sp image.Point, op Op) {
+ DrawMask(dst, r, src, sp, nil, image.Point{}, op)
+}
+
// DrawMask aligns r.Min in dst with sp in src and mp in mask and then replaces the rectangle r
// in dst with the result of a Porter-Duff composition. A nil mask is treated as opaque.
func DrawMask(dst Image, r image.Rectangle, src image.Image, sp image.Point, mask image.Image, mp image.Point, op Op) {
@@ -67,7 +107,8 @@ func DrawMask(dst Image, r image.Rectangle, src image.Image, sp image.Point, mas
}
// 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 {
+ switch dst0 := dst.(type) {
+ case *image.RGBA:
if op == Over {
if mask == nil {
switch src0 := src.(type) {
@@ -113,19 +154,20 @@ func DrawMask(dst Image, r image.Rectangle, src image.Image, sp image.Point, mas
}
drawRGBA(dst0, r, src, sp, mask, mp, op)
return
+ case *image.Paletted:
+ if op == Src && mask == nil && !processBackward(dst, r, src, sp) {
+ drawPaletted(dst0, r, src, sp, false)
+ }
}
x0, x1, dx := r.Min.X, r.Max.X, 1
y0, y1, dy := r.Min.Y, r.Max.Y, 1
- if image.Image(dst) == src && r.Overlaps(r.Add(sp.Sub(r.Min))) {
- // Rectangles overlap: process backward?
- if sp.Y < r.Min.Y || sp.Y == r.Min.Y && sp.X < r.Min.X {
- x0, x1, dx = x1-1, x0-1, -1
- y0, y1, dy = y1-1, y0-1, -1
- }
+ if processBackward(dst, r, src, sp) {
+ x0, x1, dx = x1-1, x0-1, -1
+ y0, y1, dy = y1-1, y0-1, -1
}
- var out *color.RGBA64
+ var out color.RGBA64
sy := sp.Y + y0 - r.Min.Y
my := mp.Y + y0 - r.Min.Y
for y := y0; y != y1; y, sy, my = y+dy, sy+dy, my+dy {
@@ -147,9 +189,6 @@ func DrawMask(dst Image, r image.Rectangle, src image.Image, sp image.Point, mas
dst.Set(x, y, src.At(sx, sy))
default:
sr, sg, sb, sa := src.At(sx, sy).RGBA()
- if out == nil {
- out = new(color.RGBA64)
- }
if op == Over {
dr, dg, db, da := dst.At(x, y).RGBA()
a := m - (sa * ma / m)
@@ -163,7 +202,11 @@ func DrawMask(dst Image, r image.Rectangle, src image.Image, sp image.Point, mas
out.B = uint16(sb * ma / m)
out.A = uint16(sa * ma / m)
}
- dst.Set(x, y, out)
+ // The third argument is &out instead of out (and out is
+ // declared outside of the inner loop) to avoid the implicit
+ // conversion to color.Color here allocating memory in the
+ // inner loop if sizeof(color.RGBA64) > sizeof(uintptr).
+ dst.Set(x, y, &out)
}
}
}
@@ -500,3 +543,131 @@ func drawRGBA(dst *image.RGBA, r image.Rectangle, src image.Image, sp image.Poin
i0 += dy * dst.Stride
}
}
+
+// clamp clamps i to the interval [0, 0xffff].
+func clamp(i int32) int32 {
+ if i < 0 {
+ return 0
+ }
+ if i > 0xffff {
+ return 0xffff
+ }
+ return i
+}
+
+func drawPaletted(dst Image, r image.Rectangle, src image.Image, sp image.Point, floydSteinberg bool) {
+ // TODO(nigeltao): handle the case where the dst and src overlap.
+ // Does it even make sense to try and do Floyd-Steinberg whilst
+ // walking the image backward (right-to-left bottom-to-top)?
+
+ // If dst is an *image.Paletted, we have a fast path for dst.Set and
+ // dst.At. The dst.Set equivalent is a batch version of the algorithm
+ // used by color.Palette's Index method in image/color/color.go, plus
+ // optional Floyd-Steinberg error diffusion.
+ palette, pix, stride := [][3]int32(nil), []byte(nil), 0
+ if p, ok := dst.(*image.Paletted); ok {
+ palette = make([][3]int32, len(p.Palette))
+ for i, col := range p.Palette {
+ r, g, b, _ := col.RGBA()
+ palette[i][0] = int32(r)
+ palette[i][1] = int32(g)
+ palette[i][2] = int32(b)
+ }
+ pix, stride = p.Pix[p.PixOffset(r.Min.X, r.Min.Y):], p.Stride
+ }
+
+ // quantErrorCurr and quantErrorNext are the Floyd-Steinberg quantization
+ // errors that have been propagated to the pixels in the current and next
+ // rows. The +2 simplifies calculation near the edges.
+ var quantErrorCurr, quantErrorNext [][3]int32
+ if floydSteinberg {
+ quantErrorCurr = make([][3]int32, r.Dx()+2)
+ quantErrorNext = make([][3]int32, r.Dx()+2)
+ }
+
+ // Loop over each source pixel.
+ out := color.RGBA64{A: 0xffff}
+ for y := 0; y != r.Dy(); y++ {
+ for x := 0; x != r.Dx(); x++ {
+ // er, eg and eb are the pixel's R,G,B values plus the
+ // optional Floyd-Steinberg error.
+ sr, sg, sb, _ := src.At(sp.X+x, sp.Y+y).RGBA()
+ er, eg, eb := int32(sr), int32(sg), int32(sb)
+ if floydSteinberg {
+ er = clamp(er + quantErrorCurr[x+1][0]/16)
+ eg = clamp(eg + quantErrorCurr[x+1][1]/16)
+ eb = clamp(eb + quantErrorCurr[x+1][2]/16)
+ }
+
+ if palette != nil {
+ // Find the closest palette color in Euclidean R,G,B space: the
+ // one that minimizes sum-squared-difference. We shift by 1 bit
+ // to avoid potential uint32 overflow in sum-squared-difference.
+ // TODO(nigeltao): consider smarter algorithms.
+ bestIndex, bestSSD := 0, uint32(1<<32-1)
+ for index, p := range palette {
+ delta := (er - p[0]) >> 1
+ ssd := uint32(delta * delta)
+ delta = (eg - p[1]) >> 1
+ ssd += uint32(delta * delta)
+ delta = (eb - p[2]) >> 1
+ ssd += uint32(delta * delta)
+ if ssd < bestSSD {
+ bestIndex, bestSSD = index, ssd
+ if ssd == 0 {
+ break
+ }
+ }
+ }
+ pix[y*stride+x] = byte(bestIndex)
+
+ if !floydSteinberg {
+ continue
+ }
+ er -= int32(palette[bestIndex][0])
+ eg -= int32(palette[bestIndex][1])
+ eb -= int32(palette[bestIndex][2])
+
+ } else {
+ out.R = uint16(er)
+ out.G = uint16(eg)
+ out.B = uint16(eb)
+ // The third argument is &out instead of out (and out is
+ // declared outside of the inner loop) to avoid the implicit
+ // conversion to color.Color here allocating memory in the
+ // inner loop if sizeof(color.RGBA64) > sizeof(uintptr).
+ dst.Set(r.Min.X+x, r.Min.Y+y, &out)
+
+ if !floydSteinberg {
+ continue
+ }
+ sr, sg, sb, _ = dst.At(r.Min.X+x, r.Min.Y+y).RGBA()
+ er -= int32(sr)
+ eg -= int32(sg)
+ eb -= int32(sb)
+ }
+
+ // Propagate the Floyd-Steinberg quantization error.
+ quantErrorNext[x+0][0] += er * 3
+ quantErrorNext[x+0][1] += eg * 3
+ quantErrorNext[x+0][2] += eb * 3
+ quantErrorNext[x+1][0] += er * 5
+ quantErrorNext[x+1][1] += eg * 5
+ quantErrorNext[x+1][2] += eb * 5
+ quantErrorNext[x+2][0] += er * 1
+ quantErrorNext[x+2][1] += eg * 1
+ quantErrorNext[x+2][2] += eb * 1
+ quantErrorCurr[x+2][0] += er * 7
+ quantErrorCurr[x+2][1] += eg * 7
+ quantErrorCurr[x+2][2] += eb * 7
+ }
+
+ // Recycle the quantization error buffers.
+ if floydSteinberg {
+ quantErrorCurr, quantErrorNext = quantErrorNext, quantErrorCurr
+ for i := range quantErrorNext {
+ quantErrorNext[i] = [3]int32{}
+ }
+ }
+ }
+}
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