Golang color.RGBA64類代碼示例

func getGaussianNoisePixel(k1, k2, expectation float64, pixel color.RGBA64) color.RGBA64 {
	gnPixel := color.RGBA64{}
	gnPixel.B = getGaussianNoiseValue(pixel.B, k1, k2, expectation)
	gnPixel.R = getGaussianNoiseValue(pixel.R, k1, k2, expectation)
	gnPixel.G = getGaussianNoiseValue(pixel.G, k1, k2, expectation)
	return gnPixel
}

func getLinearNoisePixel(pixel color.RGBA64, a, b uint32) color.RGBA64 {
	lnPixel := color.RGBA64{}
	lnPixel.R = getLinearNoiseValue(pixel.R, a, b)
	lnPixel.G = getLinearNoiseValue(pixel.G, a, b)
	lnPixel.B = getLinearNoiseValue(pixel.B, a, b)

	return lnPixel
}

func interpolateColor(c1, c2 color.Color, where float64) color.Color {
	r1, g1, b1, a1 := c1.RGBA()
	r2, g2, b2, a2 := c2.RGBA()

	var c color.RGBA64
	c.R = uint16(float64(r2-r1)*where + float64(r1) + 0.5)
	c.G = uint16(float64(g2-g1)*where + float64(g1) + 0.5)
	c.B = uint16(float64(b2-b1)*where + float64(b1) + 0.5)
	c.A = uint16(float64(a2-a1)*where + float64(a1) + 0.5)
	return c
}

func (burkes) Draw(dst draw.Image, r image.Rectangle, src image.Image, sp image.Point) {
	quantError0 := make([][3]int32, r.Dx()+4)
	quantError1 := make([][3]int32, r.Dx()+4)

	out := color.RGBA64{A: 0xffff}
	for y := 0; y != r.Dy(); y++ {
		for x := 0; x != r.Dx(); x++ {
			sr, sg, sb, _ := src.At(sp.X+x, sp.Y+y).RGBA()
			er, eg, eb := int32(sr), int32(sg), int32(sb)

			er = clamp(er + quantError0[x+2][0]/32)
			eg = clamp(eg + quantError0[x+2][1]/32)
			eb = clamp(eb + quantError0[x+2][2]/32)

			out.R = uint16(er)
			out.G = uint16(eg)
			out.B = uint16(eb)
			dst.Set(r.Min.X+x, r.Min.Y+y, &out)

			sr, sg, sb, _ = dst.At(r.Min.X+x, r.Min.Y+y).RGBA()
			er -= int32(sr)
			eg -= int32(sg)
			eb -= int32(sb)

			quantError0[x+3][0] += er * 8
			quantError0[x+3][1] += eg * 8
			quantError0[x+3][2] += eb * 8
			quantError0[x+4][0] += er * 4
			quantError0[x+4][1] += eg * 4
			quantError0[x+4][2] += eb * 4
			quantError1[x+0][0] += er * 2
			quantError1[x+0][1] += eg * 2
			quantError1[x+0][2] += eb * 2
			quantError1[x+1][0] += er * 4
			quantError1[x+1][1] += eg * 4
			quantError1[x+1][2] += eb * 4
			quantError1[x+2][0] += er * 8
			quantError1[x+2][1] += eg * 8
			quantError1[x+2][2] += eb * 8
			quantError1[x+3][0] += er * 4
			quantError1[x+3][1] += eg * 4
			quantError1[x+3][2] += eb * 4
			quantError1[x+4][0] += er * 2
			quantError1[x+4][1] += eg * 2
			quantError1[x+4][2] += eb * 2
		}

		// Recycle the quantization error buffers.
		quantError0, quantError1 = quantError1, quantError0
		for i := range quantError1 {
			quantError1[i] = [3]int32{}
		}
	}
}

func (z *Rasterizer) rasterizeOpSrc(dst draw.Image, r image.Rectangle, src image.Image, sp image.Point) {
	z.accumulateMask()
	out := color.RGBA64{}
	outc := color.Color(&out)
	for y, y1 := 0, r.Max.Y-r.Min.Y; y < y1; y++ {
		for x, x1 := 0, r.Max.X-r.Min.X; x < x1; x++ {
			sr, sg, sb, sa := src.At(sp.X+x, sp.Y+y).RGBA()
			ma := z.bufU32[y*z.size.X+x]

			// This algorithm comes from the standard library's image/draw
			// package.
			out.R = uint16(sr * ma / 0xffff)
			out.G = uint16(sg * ma / 0xffff)
			out.B = uint16(sb * ma / 0xffff)
			out.A = uint16(sa * ma / 0xffff)

			dst.Set(r.Min.X+x, r.Min.Y+y, outc)
		}
	}
}

func (falseFloydSteinberg) Draw(dst draw.Image, r image.Rectangle, src image.Image, sp image.Point) {
	quantErrorNext := make([][3]int32, r.Dx()+1)

	out := color.RGBA64{A: 0xffff}
	for y := 0; y != r.Dy(); y++ {
		quantError := [3]int32{}
		quantErrorNext[0] = [3]int32{}
		for x := 0; x != r.Dx(); x++ {
			sr, sg, sb, _ := src.At(sp.X+x, sp.Y+y).RGBA()
			er, eg, eb := int32(sr), int32(sg), int32(sb)

			er = clamp(er + (quantErrorNext[x][0]+quantError[0])/16)
			eg = clamp(eg + (quantErrorNext[x][1]+quantError[1])/16)
			eb = clamp(eb + (quantErrorNext[x][2]+quantError[2])/16)

			out.R = uint16(er)
			out.G = uint16(eg)
			out.B = uint16(eb)
			dst.Set(r.Min.X+x, r.Min.Y+y, &out)

			sr, sg, sb, _ = dst.At(r.Min.X+x, r.Min.Y+y).RGBA()
			er -= int32(sr)
			eg -= int32(sg)
			eb -= int32(sb)
			quantError[0] = er * 3
			quantError[1] = eg * 3
			quantError[2] = eb * 3
			quantErrorNext[x+0][0] += er * 3
			quantErrorNext[x+0][1] += eg * 3
			quantErrorNext[x+0][2] += eb * 3
			quantErrorNext[x+1][0] = er * 2
			quantErrorNext[x+1][1] = eg * 2
			quantErrorNext[x+1][2] = eb * 2
		}
	}
}

func bilinearGeneral(src image.Image, x, y float64) color.Color {
	p := findLinearSrc(src.Bounds(), x, y)
	var fr, fg, fb, fa float64
	var r, g, b, a uint32

	r, g, b, a = src.At(p.low.X, p.low.Y).RGBA()
	fr += float64(r) * p.frac00
	fg += float64(g) * p.frac00
	fb += float64(b) * p.frac00
	fa += float64(a) * p.frac00

	r, g, b, a = src.At(p.high.X, p.low.Y).RGBA()
	fr += float64(r) * p.frac01
	fg += float64(g) * p.frac01
	fb += float64(b) * p.frac01
	fa += float64(a) * p.frac01

	r, g, b, a = src.At(p.low.X, p.high.Y).RGBA()
	fr += float64(r) * p.frac10
	fg += float64(g) * p.frac10
	fb += float64(b) * p.frac10
	fa += float64(a) * p.frac10

	r, g, b, a = src.At(p.high.X, p.high.Y).RGBA()
	fr += float64(r) * p.frac11
	fg += float64(g) * p.frac11
	fb += float64(b) * p.frac11
	fa += float64(a) * p.frac11

	var c color.RGBA64
	c.R = uint16(fr + 0.5)
	c.G = uint16(fg + 0.5)
	c.B = uint16(fb + 0.5)
	c.A = uint16(fa + 0.5)
	return c
}

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
//.........這裏部分代碼省略.........

// 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)
//.........這裏部分代碼省略.........

// 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.
	if dst0, ok := dst.(*image.RGBA); ok {
		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 *ycbcr.YCbCr:
					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 *ycbcr.YCbCr:
					drawYCbCr(dst0, r, src0, sp)
					return
				}
			}
		}
		drawRGBA(dst0, r, src, sp, mask, mp, op)
		return
	}

	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
		}
	}

	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 out == nil {
					out = new(color.RGBA64)
				}
				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)
//.........這裏部分代碼省略.........

// readImagePass reads a single image pass, sized according to the pass number.
func (d *decoder) readImagePass(r io.Reader, pass int, allocateOnly bool) (image.Image, error) {
	var bitsPerPixel int = 0
	pixOffset := 0
	var (
		gray     *image.Gray
		rgba     *image.RGBA
		paletted *image.Paletted
		nrgba    *image.NRGBA
		gray16   *image.Gray16
		rgba64   *image.RGBA64
		nrgba64  *image.NRGBA64
		img      image.Image
	)
	width, height := d.width, d.height
	if d.interlace == itAdam7 && !allocateOnly {
		p := interlacing[pass]
		// Add the multiplication factor and subtract one, effectively rounding up.
		width = (width - p.xOffset + p.xFactor - 1) / p.xFactor
		height = (height - p.yOffset + p.yFactor - 1) / p.yFactor
	}
	switch d.cb {
	case cbG1, cbG2, cbG4, cbG8:
		bitsPerPixel = d.depth
		gray = image.NewGray(image.Rect(0, 0, width, height))
		img = gray
	case cbGA8:
		bitsPerPixel = 16
		nrgba = image.NewNRGBA(image.Rect(0, 0, width, height))
		img = nrgba
	case cbTC8:
		bitsPerPixel = 24
		rgba = image.NewRGBA(image.Rect(0, 0, width, height))
		img = rgba
	case cbP1, cbP2, cbP4, cbP8:
		bitsPerPixel = d.depth
		paletted = image.NewPaletted(image.Rect(0, 0, width, height), d.palette)
		img = paletted
	case cbTCA8:
		bitsPerPixel = 32
		nrgba = image.NewNRGBA(image.Rect(0, 0, width, height))
		img = nrgba
	case cbG16:
		bitsPerPixel = 16
		gray16 = image.NewGray16(image.Rect(0, 0, width, height))
		img = gray16
	case cbGA16:
		bitsPerPixel = 32
		nrgba64 = image.NewNRGBA64(image.Rect(0, 0, width, height))
		img = nrgba64
	case cbTC16:
		bitsPerPixel = 48
		rgba64 = image.NewRGBA64(image.Rect(0, 0, width, height))
		img = rgba64
	case cbTCA16:
		bitsPerPixel = 64
		nrgba64 = image.NewNRGBA64(image.Rect(0, 0, width, height))
		img = nrgba64
	}
	if allocateOnly {
		return img, nil
	}
	bytesPerPixel := (bitsPerPixel + 7) / 8

	// The +1 is for the per-row filter type, which is at cr[0].
	rowSize := 1 + (bitsPerPixel*width+7)/8
	// cr and pr are the bytes for the current and previous row.
	cr := make([]uint8, rowSize)
	pr := make([]uint8, rowSize)

	for y := 0; y < height; y++ {
		// Read the decompressed bytes.
		_, err := io.ReadFull(r, cr)
		if err != nil {
			if err == io.EOF || err == io.ErrUnexpectedEOF {
				return nil, FormatError("not enough pixel data")
			}
			return nil, err
		}

		// Apply the filter.
		cdat := cr[1:]
		pdat := pr[1:]
		switch cr[0] {
		case ftNone:
			// No-op.
		case ftSub:
			for i := bytesPerPixel; i < len(cdat); i++ {
				cdat[i] += cdat[i-bytesPerPixel]
			}
		case ftUp:
			for i, p := range pdat {
				cdat[i] += p
			}
		case ftAverage:
			for i := 0; i < bytesPerPixel; i++ {
				cdat[i] += pdat[i] / 2
			}
			for i := bytesPerPixel; i < len(cdat); i++ {
				cdat[i] += uint8((int(cdat[i-bytesPerPixel]) + int(pdat[i])) / 2)
//.........這裏部分代碼省略.........

// 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.
// The implementation is simple and slow.
// TODO(nigeltao): Optimize this.
func DrawMask(dst Image, r Rectangle, src image.Image, sp Point, mask image.Image, mp Point, op Op) {
	dx, dy := src.Width()-sp.X, src.Height()-sp.Y
	if mask != nil {
		if dx > mask.Width()-mp.X {
			dx = mask.Width() - mp.X
		}
		if dy > mask.Height()-mp.Y {
			dy = mask.Height() - mp.Y
		}
	}
	if r.Dx() > dx {
		r.Max.X = r.Min.X + dx
	}
	if r.Dy() > dy {
		r.Max.Y = r.Min.Y + dy
	}

	// TODO(nigeltao): Clip r to dst's bounding box, and handle the case when sp or mp has negative X or Y.
	// TODO(nigeltao): Ensure that r is well formed, i.e. r.Max.X >= r.Min.X and likewise for Y.

	// 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 {
				if src0, ok := src.(image.Uniform); 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.Uniform); ok {
					drawGlyphOver(dst0, r, src0, mask0, mp)
					return
				}
			}
		} else {
			if mask == nil {
				if src0, ok := src.(image.Uniform); ok {
					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 {
						drawCopySrc(dst0, r, src0, sp)
						return
					}
				}
			}
		}
		drawRGBA(dst0, r, src, sp, mask, mp, op)
		return
	case DrawMasker:
		// Destination might wish to perform the draw operation itself
		if dst0.DrawMask(r, src, sp, mask, mp, op) {
			return
		}
	}
	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
		}
	}

	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, zeroColor)
				}
			case ma == m && op == Src:
//.........這裏部分代碼省略.........