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-rw-r--r--src/image/draw/draw.go673
1 files changed, 673 insertions, 0 deletions
diff --git a/src/image/draw/draw.go b/src/image/draw/draw.go
new file mode 100644
index 000000000..661230e7c
--- /dev/null
+++ b/src/image/draw/draw.go
@@ -0,0 +1,673 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package draw provides image composition functions.
+//
+// See "The Go image/draw package" for an introduction to this package:
+// http://golang.org/doc/articles/image_draw.html
+package draw
+
+import (
+ "image"
+ "image/color"
+)
+
+// 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
+
+const (
+ // Over specifies ``(src in mask) over dst''.
+ Over Op = iota
+ // Src specifies ``src in mask''.
+ Src
+)
+
+// 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)
+}
+
+// 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
+// destination image's co-ordinate space) and shifts the points sp and mp by
+// the same amount as the change in r.Min.
+func clip(dst Image, r *image.Rectangle, src image.Image, sp *image.Point, mask image.Image, mp *image.Point) {
+ orig := r.Min
+ *r = r.Intersect(dst.Bounds())
+ *r = r.Intersect(src.Bounds().Add(orig.Sub(*sp)))
+ if mask != nil {
+ *r = r.Intersect(mask.Bounds().Add(orig.Sub(*mp)))
+ }
+ dx := r.Min.X - orig.X
+ dy := r.Min.Y - orig.Y
+ if dx == 0 && dy == 0 {
+ return
+ }
+ (*sp).X += dx
+ (*sp).Y += dy
+ (*mp).X += dx
+ (*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) {
+ clip(dst, &r, src, &sp, mask, &mp)
+ if r.Empty() {
+ return
+ }
+
+ // Fast paths for special cases. If none of them apply, then we fall back to a general but slow implementation.
+ switch dst0 := dst.(type) {
+ case *image.RGBA:
+ if op == Over {
+ if mask == nil {
+ switch src0 := src.(type) {
+ case *image.Uniform:
+ drawFillOver(dst0, r, src0)
+ return
+ case *image.RGBA:
+ drawCopyOver(dst0, r, src0, sp)
+ return
+ case *image.NRGBA:
+ drawNRGBAOver(dst0, r, src0, sp)
+ return
+ case *image.YCbCr:
+ if drawYCbCr(dst0, r, src0, sp) {
+ return
+ }
+ }
+ } else if mask0, ok := mask.(*image.Alpha); ok {
+ switch src0 := src.(type) {
+ case *image.Uniform:
+ drawGlyphOver(dst0, r, src0, mask0, mp)
+ return
+ }
+ }
+ } else {
+ if mask == nil {
+ switch src0 := src.(type) {
+ case *image.Uniform:
+ drawFillSrc(dst0, r, src0)
+ return
+ case *image.RGBA:
+ drawCopySrc(dst0, r, src0, sp)
+ return
+ case *image.NRGBA:
+ drawNRGBASrc(dst0, r, src0, sp)
+ return
+ case *image.YCbCr:
+ if drawYCbCr(dst0, r, src0, sp) {
+ return
+ }
+ }
+ }
+ }
+ 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 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
+ 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 {
+ 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 {
+ ma := uint32(m)
+ if mask != nil {
+ _, _, _, ma = mask.At(mx, my).RGBA()
+ }
+ switch {
+ case ma == 0:
+ if op == Over {
+ // No-op.
+ } else {
+ dst.Set(x, y, color.Transparent)
+ }
+ 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)
+ } 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)
+ }
+ // 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)
+ }
+ }
+ }
+}
+
+func drawFillOver(dst *image.RGBA, r image.Rectangle, src *image.Uniform) {
+ sr, sg, sb, sa := src.RGBA()
+ // The 0x101 is here for the same reason as in drawRGBA.
+ a := (m - sa) * 0x101
+ i0 := dst.PixOffset(r.Min.X, r.Min.Y)
+ i1 := i0 + r.Dx()*4
+ for y := r.Min.Y; y != r.Max.Y; y++ {
+ for i := i0; i < i1; i += 4 {
+ dr := uint32(dst.Pix[i+0])
+ dg := uint32(dst.Pix[i+1])
+ db := uint32(dst.Pix[i+2])
+ da := uint32(dst.Pix[i+3])
+
+ dst.Pix[i+0] = uint8((dr*a/m + sr) >> 8)
+ dst.Pix[i+1] = uint8((dg*a/m + sg) >> 8)
+ dst.Pix[i+2] = uint8((db*a/m + sb) >> 8)
+ dst.Pix[i+3] = uint8((da*a/m + sa) >> 8)
+ }
+ i0 += dst.Stride
+ i1 += dst.Stride
+ }
+}
+
+func drawFillSrc(dst *image.RGBA, r image.Rectangle, src *image.Uniform) {
+ sr, sg, sb, sa := src.RGBA()
+ // 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.
+ i0 := dst.PixOffset(r.Min.X, r.Min.Y)
+ i1 := i0 + r.Dx()*4
+ for i := i0; i < i1; i += 4 {
+ dst.Pix[i+0] = uint8(sr >> 8)
+ dst.Pix[i+1] = uint8(sg >> 8)
+ dst.Pix[i+2] = uint8(sb >> 8)
+ dst.Pix[i+3] = uint8(sa >> 8)
+ }
+ firstRow := dst.Pix[i0:i1]
+ for y := r.Min.Y + 1; y < r.Max.Y; y++ {
+ i0 += dst.Stride
+ i1 += dst.Stride
+ copy(dst.Pix[i0:i1], firstRow)
+ }
+}
+
+func drawCopyOver(dst *image.RGBA, r image.Rectangle, src *image.RGBA, sp image.Point) {
+ dx, dy := r.Dx(), r.Dy()
+ d0 := dst.PixOffset(r.Min.X, r.Min.Y)
+ s0 := src.PixOffset(sp.X, sp.Y)
+ var (
+ ddelta, sdelta int
+ i0, i1, idelta int
+ )
+ if r.Min.Y < sp.Y || r.Min.Y == sp.Y && r.Min.X <= sp.X {
+ ddelta = dst.Stride
+ sdelta = src.Stride
+ i0, i1, idelta = 0, dx*4, +4
+ } else {
+ // If the source start point is higher than the destination start point, or equal height but to the left,
+ // then we compose the rows in right-to-left, bottom-up order instead of left-to-right, top-down.
+ d0 += (dy - 1) * dst.Stride
+ s0 += (dy - 1) * src.Stride
+ ddelta = -dst.Stride
+ sdelta = -src.Stride
+ i0, i1, idelta = (dx-1)*4, -4, -4
+ }
+ for ; dy > 0; dy-- {
+ dpix := dst.Pix[d0:]
+ spix := src.Pix[s0:]
+ for i := i0; i != i1; i += idelta {
+ sr := uint32(spix[i+0]) * 0x101
+ sg := uint32(spix[i+1]) * 0x101
+ sb := uint32(spix[i+2]) * 0x101
+ sa := uint32(spix[i+3]) * 0x101
+
+ dr := uint32(dpix[i+0])
+ dg := uint32(dpix[i+1])
+ db := uint32(dpix[i+2])
+ da := uint32(dpix[i+3])
+
+ // The 0x101 is here for the same reason as in drawRGBA.
+ a := (m - sa) * 0x101
+
+ dpix[i+0] = uint8((dr*a/m + sr) >> 8)
+ dpix[i+1] = uint8((dg*a/m + sg) >> 8)
+ dpix[i+2] = uint8((db*a/m + sb) >> 8)
+ dpix[i+3] = uint8((da*a/m + sa) >> 8)
+ }
+ d0 += ddelta
+ s0 += sdelta
+ }
+}
+
+func drawCopySrc(dst *image.RGBA, r image.Rectangle, src *image.RGBA, sp image.Point) {
+ n, dy := 4*r.Dx(), r.Dy()
+ d0 := dst.PixOffset(r.Min.X, r.Min.Y)
+ s0 := src.PixOffset(sp.X, sp.Y)
+ var ddelta, sdelta int
+ if r.Min.Y <= sp.Y {
+ ddelta = dst.Stride
+ sdelta = src.Stride
+ } else {
+ // If the source start point is higher than the destination start point, then we compose the rows
+ // in bottom-up order instead of top-down. Unlike the drawCopyOver function, we don't have to
+ // check the x co-ordinates because the built-in copy function can handle overlapping slices.
+ d0 += (dy - 1) * dst.Stride
+ s0 += (dy - 1) * src.Stride
+ ddelta = -dst.Stride
+ sdelta = -src.Stride
+ }
+ for ; dy > 0; dy-- {
+ copy(dst.Pix[d0:d0+n], src.Pix[s0:s0+n])
+ d0 += ddelta
+ s0 += sdelta
+ }
+}
+
+func drawNRGBAOver(dst *image.RGBA, r image.Rectangle, src *image.NRGBA, sp image.Point) {
+ i0 := (r.Min.X - dst.Rect.Min.X) * 4
+ i1 := (r.Max.X - dst.Rect.Min.X) * 4
+ si0 := (sp.X - src.Rect.Min.X) * 4
+ yMax := r.Max.Y - dst.Rect.Min.Y
+
+ y := r.Min.Y - dst.Rect.Min.Y
+ sy := sp.Y - src.Rect.Min.Y
+ for ; y != yMax; y, sy = y+1, sy+1 {
+ dpix := dst.Pix[y*dst.Stride:]
+ spix := src.Pix[sy*src.Stride:]
+
+ for i, si := i0, si0; i < i1; i, si = i+4, si+4 {
+ // Convert from non-premultiplied color to pre-multiplied color.
+ sa := uint32(spix[si+3]) * 0x101
+ sr := uint32(spix[si+0]) * sa / 0xff
+ sg := uint32(spix[si+1]) * sa / 0xff
+ sb := uint32(spix[si+2]) * sa / 0xff
+
+ dr := uint32(dpix[i+0])
+ dg := uint32(dpix[i+1])
+ db := uint32(dpix[i+2])
+ da := uint32(dpix[i+3])
+
+ // The 0x101 is here for the same reason as in drawRGBA.
+ a := (m - sa) * 0x101
+
+ dpix[i+0] = uint8((dr*a/m + sr) >> 8)
+ dpix[i+1] = uint8((dg*a/m + sg) >> 8)
+ dpix[i+2] = uint8((db*a/m + sb) >> 8)
+ dpix[i+3] = uint8((da*a/m + sa) >> 8)
+ }
+ }
+}
+
+func drawNRGBASrc(dst *image.RGBA, r image.Rectangle, src *image.NRGBA, sp image.Point) {
+ i0 := (r.Min.X - dst.Rect.Min.X) * 4
+ i1 := (r.Max.X - dst.Rect.Min.X) * 4
+ si0 := (sp.X - src.Rect.Min.X) * 4
+ yMax := r.Max.Y - dst.Rect.Min.Y
+
+ y := r.Min.Y - dst.Rect.Min.Y
+ sy := sp.Y - src.Rect.Min.Y
+ for ; y != yMax; y, sy = y+1, sy+1 {
+ dpix := dst.Pix[y*dst.Stride:]
+ spix := src.Pix[sy*src.Stride:]
+
+ for i, si := i0, si0; i < i1; i, si = i+4, si+4 {
+ // Convert from non-premultiplied color to pre-multiplied color.
+ sa := uint32(spix[si+3]) * 0x101
+ sr := uint32(spix[si+0]) * sa / 0xff
+ sg := uint32(spix[si+1]) * sa / 0xff
+ sb := uint32(spix[si+2]) * sa / 0xff
+
+ dpix[i+0] = uint8(sr >> 8)
+ dpix[i+1] = uint8(sg >> 8)
+ dpix[i+2] = uint8(sb >> 8)
+ dpix[i+3] = uint8(sa >> 8)
+ }
+ }
+}
+
+func drawYCbCr(dst *image.RGBA, r image.Rectangle, src *image.YCbCr, sp image.Point) (ok bool) {
+ // An image.YCbCr is always fully opaque, and so if the mask is implicitly nil
+ // (i.e. fully opaque) then the op is effectively always Src.
+ x0 := (r.Min.X - dst.Rect.Min.X) * 4
+ x1 := (r.Max.X - dst.Rect.Min.X) * 4
+ y0 := r.Min.Y - dst.Rect.Min.Y
+ y1 := r.Max.Y - dst.Rect.Min.Y
+ switch src.SubsampleRatio {
+ case image.YCbCrSubsampleRatio444:
+ for y, sy := y0, sp.Y; y != y1; y, sy = y+1, sy+1 {
+ dpix := dst.Pix[y*dst.Stride:]
+ yi := (sy-src.Rect.Min.Y)*src.YStride + (sp.X - src.Rect.Min.X)
+ ci := (sy-src.Rect.Min.Y)*src.CStride + (sp.X - src.Rect.Min.X)
+ for x := x0; x != x1; x, yi, ci = x+4, yi+1, ci+1 {
+ rr, gg, bb := color.YCbCrToRGB(src.Y[yi], src.Cb[ci], src.Cr[ci])
+ dpix[x+0] = rr
+ dpix[x+1] = gg
+ dpix[x+2] = bb
+ dpix[x+3] = 255
+ }
+ }
+ case image.YCbCrSubsampleRatio422:
+ for y, sy := y0, sp.Y; y != y1; y, sy = y+1, sy+1 {
+ dpix := dst.Pix[y*dst.Stride:]
+ yi := (sy-src.Rect.Min.Y)*src.YStride + (sp.X - src.Rect.Min.X)
+ ciBase := (sy-src.Rect.Min.Y)*src.CStride - src.Rect.Min.X/2
+ for x, sx := x0, sp.X; x != x1; x, sx, yi = x+4, sx+1, yi+1 {
+ ci := ciBase + sx/2
+ rr, gg, bb := color.YCbCrToRGB(src.Y[yi], src.Cb[ci], src.Cr[ci])
+ dpix[x+0] = rr
+ dpix[x+1] = gg
+ dpix[x+2] = bb
+ dpix[x+3] = 255
+ }
+ }
+ case image.YCbCrSubsampleRatio420:
+ for y, sy := y0, sp.Y; y != y1; y, sy = y+1, sy+1 {
+ dpix := dst.Pix[y*dst.Stride:]
+ yi := (sy-src.Rect.Min.Y)*src.YStride + (sp.X - src.Rect.Min.X)
+ ciBase := (sy/2-src.Rect.Min.Y/2)*src.CStride - src.Rect.Min.X/2
+ for x, sx := x0, sp.X; x != x1; x, sx, yi = x+4, sx+1, yi+1 {
+ ci := ciBase + sx/2
+ rr, gg, bb := color.YCbCrToRGB(src.Y[yi], src.Cb[ci], src.Cr[ci])
+ dpix[x+0] = rr
+ dpix[x+1] = gg
+ dpix[x+2] = bb
+ dpix[x+3] = 255
+ }
+ }
+ case image.YCbCrSubsampleRatio440:
+ for y, sy := y0, sp.Y; y != y1; y, sy = y+1, sy+1 {
+ dpix := dst.Pix[y*dst.Stride:]
+ yi := (sy-src.Rect.Min.Y)*src.YStride + (sp.X - src.Rect.Min.X)
+ ci := (sy/2-src.Rect.Min.Y/2)*src.CStride + (sp.X - src.Rect.Min.X)
+ for x := x0; x != x1; x, yi, ci = x+4, yi+1, ci+1 {
+ rr, gg, bb := color.YCbCrToRGB(src.Y[yi], src.Cb[ci], src.Cr[ci])
+ dpix[x+0] = rr
+ dpix[x+1] = gg
+ dpix[x+2] = bb
+ dpix[x+3] = 255
+ }
+ }
+ default:
+ return false
+ }
+ return true
+}
+
+func drawGlyphOver(dst *image.RGBA, r image.Rectangle, src *image.Uniform, mask *image.Alpha, mp image.Point) {
+ i0 := dst.PixOffset(r.Min.X, r.Min.Y)
+ i1 := i0 + r.Dx()*4
+ mi0 := mask.PixOffset(mp.X, mp.Y)
+ sr, sg, sb, sa := src.RGBA()
+ for y, my := r.Min.Y, mp.Y; y != r.Max.Y; y, my = y+1, my+1 {
+ for i, mi := i0, mi0; i < i1; i, mi = i+4, mi+1 {
+ ma := uint32(mask.Pix[mi])
+ if ma == 0 {
+ continue
+ }
+ ma |= ma << 8
+
+ dr := uint32(dst.Pix[i+0])
+ dg := uint32(dst.Pix[i+1])
+ db := uint32(dst.Pix[i+2])
+ da := uint32(dst.Pix[i+3])
+
+ // The 0x101 is here for the same reason as in drawRGBA.
+ a := (m - (sa * ma / m)) * 0x101
+
+ dst.Pix[i+0] = uint8((dr*a + sr*ma) / m >> 8)
+ dst.Pix[i+1] = uint8((dg*a + sg*ma) / m >> 8)
+ dst.Pix[i+2] = uint8((db*a + sb*ma) / m >> 8)
+ dst.Pix[i+3] = uint8((da*a + sa*ma) / m >> 8)
+ }
+ i0 += dst.Stride
+ i1 += dst.Stride
+ mi0 += mask.Stride
+ }
+}
+
+func drawRGBA(dst *image.RGBA, r image.Rectangle, src image.Image, sp image.Point, mask image.Image, mp image.Point, op Op) {
+ 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))) {
+ 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
+ }
+ }
+
+ sy := sp.Y + y0 - r.Min.Y
+ my := mp.Y + y0 - r.Min.Y
+ sx0 := sp.X + x0 - r.Min.X
+ mx0 := mp.X + x0 - r.Min.X
+ sx1 := sx0 + (x1 - x0)
+ i0 := dst.PixOffset(x0, y0)
+ di := dx * 4
+ for y := y0; y != y1; y, sy, my = y+dy, sy+dy, my+dy {
+ for i, sx, mx := i0, sx0, mx0; sx != sx1; i, sx, mx = i+di, sx+dx, mx+dx {
+ ma := uint32(m)
+ if mask != nil {
+ _, _, _, ma = mask.At(mx, my).RGBA()
+ }
+ sr, sg, sb, sa := src.At(sx, sy).RGBA()
+ if op == Over {
+ dr := uint32(dst.Pix[i+0])
+ dg := uint32(dst.Pix[i+1])
+ db := uint32(dst.Pix[i+2])
+ da := uint32(dst.Pix[i+3])
+
+ // dr, dg, db and da are all 8-bit color at the moment, ranging in [0,255].
+ // We work in 16-bit color, and so would normally do:
+ // dr |= dr << 8
+ // 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
+
+ dst.Pix[i+0] = uint8((dr*a + sr*ma) / m >> 8)
+ dst.Pix[i+1] = uint8((dg*a + sg*ma) / m >> 8)
+ dst.Pix[i+2] = uint8((db*a + sb*ma) / m >> 8)
+ dst.Pix[i+3] = uint8((da*a + sa*ma) / m >> 8)
+
+ } else {
+ dst.Pix[i+0] = uint8(sr * ma / m >> 8)
+ dst.Pix[i+1] = uint8(sg * ma / m >> 8)
+ dst.Pix[i+2] = uint8(sb * ma / m >> 8)
+ dst.Pix[i+3] = uint8(sa * ma / m >> 8)
+ }
+ }
+ 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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