Golang Paletted.ColorIndexAt方法代碼示例

func modeTerrain(p *image.Paletted, l int) uint8 {
	b := p.Bounds()
	modeMap := make([]uint8, l)
	var most, mode uint8
	for i := b.Min.X; i < b.Max.X; i++ {
		for j := b.Min.Y; j < b.Max.Y; j++ {
			pos := p.ColorIndexAt(i, j)
			modeMap[pos]++
			if m := modeMap[pos]; m > most {
				most = m
				mode = pos
			}
		}
	}
	return mode
}

//.........這裏部分代碼省略.........
		paletted = png.(*image.Paletted)
	}

	// Write the filename and IHDR.
	io.WriteString(w, "#SNG: from "+filename+".png\nIHDR {\n")
	fmt.Fprintf(w, "    width: %d; height: %d; bitdepth: %d;\n", bounds.Dx(), bounds.Dy(), bitdepth)
	switch {
	case cm == color.RGBAModel, cm == color.RGBA64Model:
		io.WriteString(w, "    using color;\n")
	case cm == color.NRGBAModel, cm == color.NRGBA64Model:
		io.WriteString(w, "    using color alpha;\n")
	case cm == color.GrayModel, cm == color.Gray16Model:
		io.WriteString(w, "    using grayscale;\n")
	case cpm != nil:
		io.WriteString(w, "    using color palette;\n")
	default:
		io.WriteString(w, "unknown PNG decoder color model\n")
	}
	io.WriteString(w, "}\n")

	// We fake a gAMA output. The test files have a gAMA chunk but the go PNG parser ignores it
	// (the PNG spec section 11.3 says "Ancillary chunks may be ignored by a decoder").
	io.WriteString(w, "gAMA {1.0000}\n")

	// Write the PLTE and tRNS (if applicable).
	if cpm != nil {
		lastAlpha := -1
		io.WriteString(w, "PLTE {\n")
		for i, c := range cpm {
			r, g, b, a := c.RGBA()
			if a != 0xffff {
				lastAlpha = i
			}
			r >>= 8
			g >>= 8
			b >>= 8
			fmt.Fprintf(w, "    (%3d,%3d,%3d)     # rgb = (0x%02x,0x%02x,0x%02x)\n", r, g, b, r, g, b)
		}
		io.WriteString(w, "}\n")
		if lastAlpha != -1 {
			io.WriteString(w, "tRNS {\n")
			for i := 0; i <= lastAlpha; i++ {
				_, _, _, a := cpm[i].RGBA()
				a >>= 8
				fmt.Fprintf(w, " %d", a)
			}
			io.WriteString(w, "}\n")
		}
	}

	// Write the IMAGE.
	io.WriteString(w, "IMAGE {\n    pixels hex\n")
	for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
		switch {
		case cm == color.GrayModel:
			for x := bounds.Min.X; x < bounds.Max.X; x++ {
				gray := png.At(x, y).(color.Gray)
				fmt.Fprintf(w, "%02x", gray.Y)
			}
		case cm == color.Gray16Model:
			for x := bounds.Min.X; x < bounds.Max.X; x++ {
				gray16 := png.At(x, y).(color.Gray16)
				fmt.Fprintf(w, "%04x ", gray16.Y)
			}
		case cm == color.RGBAModel:
			for x := bounds.Min.X; x < bounds.Max.X; x++ {
				rgba := png.At(x, y).(color.RGBA)
				fmt.Fprintf(w, "%02x%02x%02x ", rgba.R, rgba.G, rgba.B)
			}
		case cm == color.RGBA64Model:
			for x := bounds.Min.X; x < bounds.Max.X; x++ {
				rgba64 := png.At(x, y).(color.RGBA64)
				fmt.Fprintf(w, "%04x%04x%04x ", rgba64.R, rgba64.G, rgba64.B)
			}
		case cm == color.NRGBAModel:
			for x := bounds.Min.X; x < bounds.Max.X; x++ {
				nrgba := png.At(x, y).(color.NRGBA)
				fmt.Fprintf(w, "%02x%02x%02x%02x ", nrgba.R, nrgba.G, nrgba.B, nrgba.A)
			}
		case cm == color.NRGBA64Model:
			for x := bounds.Min.X; x < bounds.Max.X; x++ {
				nrgba64 := png.At(x, y).(color.NRGBA64)
				fmt.Fprintf(w, "%04x%04x%04x%04x ", nrgba64.R, nrgba64.G, nrgba64.B, nrgba64.A)
			}
		case cpm != nil:
			var b, c int
			for x := bounds.Min.X; x < bounds.Max.X; x++ {
				b = b<<uint(bitdepth) | int(paletted.ColorIndexAt(x, y))
				c++
				if c == 8/bitdepth {
					fmt.Fprintf(w, "%02x", b)
					b = 0
					c = 0
				}
			}
		}
		io.WriteString(w, "\n")
	}
	io.WriteString(w, "}\n")
}

func writeImage(w io.Writer, m image.Image, ct uint8) os.Error {
	zw, err := zlib.NewDeflater(w)
	if err != nil {
		return err
	}
	defer zw.Close()

	bpp := 0 // Bytes per pixel.
	var paletted *image.Paletted
	switch ct {
	case ctTrueColor:
		bpp = 3
	case ctPaletted:
		bpp = 1
		paletted = m.(*image.Paletted)
	case ctTrueColorAlpha:
		bpp = 4
	}
	// cr[*] and pr are the bytes for the current and previous row.
	// cr[0] is unfiltered (or equivalently, filtered with the ftNone filter).
	// cr[ft], for non-zero filter types ft, are buffers for transforming cr[0] under the
	// other PNG filter types. These buffers are allocated once and re-used for each row.
	// The +1 is for the per-row filter type, which is at cr[*][0].
	var cr [nFilter][]uint8
	for i := 0; i < len(cr); i++ {
		cr[i] = make([]uint8, 1+bpp*m.Width())
		cr[i][0] = uint8(i)
	}
	pr := make([]uint8, 1+bpp*m.Width())

	for y := 0; y < m.Height(); y++ {
		// Convert from colors to bytes.
		switch ct {
		case ctTrueColor:
			for x := 0; x < m.Width(); x++ {
				// We have previously verified that the alpha value is fully opaque.
				r, g, b, _ := m.At(x, y).RGBA()
				cr[0][3*x+1] = uint8(r >> 24)
				cr[0][3*x+2] = uint8(g >> 24)
				cr[0][3*x+3] = uint8(b >> 24)
			}
		case ctPaletted:
			for x := 0; x < m.Width(); x++ {
				cr[0][x+1] = paletted.ColorIndexAt(x, y)
			}
		case ctTrueColorAlpha:
			// Convert from image.Image (which is alpha-premultiplied) to PNG's non-alpha-premultiplied.
			for x := 0; x < m.Width(); x++ {
				c := image.NRGBAColorModel.Convert(m.At(x, y)).(image.NRGBAColor)
				cr[0][4*x+1] = c.R
				cr[0][4*x+2] = c.G
				cr[0][4*x+3] = c.B
				cr[0][4*x+4] = c.A
			}
		}

		// Apply the filter.
		f := filter(cr[0:nFilter], pr, bpp)

		// Write the compressed bytes.
		_, err = zw.Write(cr[f])
		if err != nil {
			return err
		}

		// The current row for y is the previous row for y+1.
		pr, cr[0] = cr[0], pr
	}
	return nil
}

func (g *generator) buildTerrain(mpath minecraft.Path, level *level, terrain, biomes, plants *image.Paletted, height, water *image.Gray, c chan paint) error {
	b := terrain.Bounds()
	proceed := make(chan uint8, 10)
	errChan := make(chan error, 1)
	go func() {
		defer close(proceed)
		cc := newCache(g.Terrain.Blocks)
		for j := 0; j < b.Max.Y; j += 16 {
			chunkZ := int32(j >> 4)
			for i := 0; i < b.Max.X; i += 16 {
				chunkX := int32(i >> 4)
				h := int32(meanHeight(height.SubImage(image.Rect(i, j, i+16, j+16)).(*image.Gray)))
				wh := int32(meanHeight(water.SubImage(image.Rect(i, j, i+16, j+16)).(*image.Gray)))
				var t uint8
				if wh >= h<<1 { // more water than land...
					c <- paint{
						color.RGBA{0, 0, 255, 255},
						chunkX, chunkZ,
					}
					t = uint8(len(g.Terrain.Blocks) - 1)
					h = wh
				} else {
					t = modeTerrain(terrain.SubImage(image.Rect(i, j, i+16, j+16)).(*image.Paletted), len(g.Terrain.Palette))
					c <- paint{
						g.Terrain.Palette[t],
						chunkX, chunkZ,
					}
				}
				if err := mpath.SetChunk(cc.getFromCache(chunkX, chunkZ, t, h)); err != nil {
					errChan <- err
					return
				}
				proceed <- t
			}
		}
	}()
	ts := make([]uint8, 0, 1024)
	for i := 0; i < (b.Max.X>>4)+2; i++ {
		ts = append(ts, <-proceed) // get far enough ahead so all chunks are surrounded before shaping, to get correct lighting
	}
	select {
	case err := <-errChan:
		return err
	default:
	}
	for j := int32(0); j < int32(b.Max.Y); j += 16 {
		chunkZ := j >> 4
		for i := int32(0); i < int32(b.Max.X); i += 16 {
			chunkX := i >> 4
			var totalHeight int32
			ot := ts[0]
			ts = ts[1:]
			oy, _ := level.GetHeight(i, j)
			for x := i; x < i+16; x++ {
				for z := j; z < j+16; z++ {
					if biomes != nil {
						level.SetBiome(x, z, g.Biomes.Values[biomes.ColorIndexAt(int(x), int(z))])
					}
					h := int32(height.GrayAt(int(x), int(z)).Y)
					totalHeight += h
					wl := int32(water.GrayAt(int(x), int(z)).Y)
					y := oy
					if h > y {
						y = h
					}
					if wl > y {
						y = wl
					}
					for ; y > h && y > wl; y-- {
						level.SetBlock(x, y, z, minecraft.Block{})
					}
					if plants != nil {
						p := g.Plants.Blocks[plants.ColorIndexAt(int(x), int(z))]
						py := int32(1)
						for ; py <= int32(p.Level); py++ {
							level.SetBlock(x, y+py, z, p.Base)
						}
						level.SetBlock(x, y+py, z, p.Top)
					}
					for ; y > h; y-- {
						level.SetBlock(x, y, z, minecraft.Block{ID: 9})
					}
					t := terrain.ColorIndexAt(int(x), int(z))
					tb := g.Terrain.Blocks[t]
					for ; y > h-int32(tb.Level); y-- {
						level.SetBlock(x, y, z, tb.Top)
					}
					if t != ot {
						h = 0
					} else {
						h = oy
					}
					for ; y >= h; y-- {
						level.SetBlock(x, y, z, tb.Base)
					}
				}
			}
			c <- paint{
				color.Alpha{uint8(totalHeight >> 8)},
				chunkX, chunkZ,
//.........這裏部分代碼省略.........

//.........這裏部分代碼省略.........
					// The standard image package doesn't have a "gray with
					// alpha" type. Instead, we use an image.NRGBA.
					fmt.Fprintf(w, "    gray: %d;\n", c.R)
				default:
					fmt.Fprintf(w, "    red: %d; green: %d; blue: %d;\n", c.R, c.G, c.B)
				}
				io.WriteString(w, "}\n")
			}
		case color.NRGBA64:
			if c.A == 0 {
				useTransparent = true
				io.WriteString(w, "tRNS {\n")
				switch filename {
				case "ftbwn0g16":
					// The standard image package doesn't have a "gray16 with
					// alpha" type. Instead, we use an image.NRGBA64.
					fmt.Fprintf(w, "    gray: %d;\n", c.R)
				default:
					fmt.Fprintf(w, "    red: %d; green: %d; blue: %d;\n", c.R, c.G, c.B)
				}
				io.WriteString(w, "}\n")
			}
		}
	}

	// Write the IMAGE.
	io.WriteString(w, "IMAGE {\n    pixels hex\n")
	for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
		switch {
		case cm == color.GrayModel:
			for x := bounds.Min.X; x < bounds.Max.X; x++ {
				gray := png.At(x, y).(color.Gray)
				fmt.Fprintf(w, "%02x", gray.Y)
			}
		case cm == color.Gray16Model:
			for x := bounds.Min.X; x < bounds.Max.X; x++ {
				gray16 := png.At(x, y).(color.Gray16)
				fmt.Fprintf(w, "%04x ", gray16.Y)
			}
		case cm == color.RGBAModel:
			for x := bounds.Min.X; x < bounds.Max.X; x++ {
				rgba := png.At(x, y).(color.RGBA)
				fmt.Fprintf(w, "%02x%02x%02x ", rgba.R, rgba.G, rgba.B)
			}
		case cm == color.RGBA64Model:
			for x := bounds.Min.X; x < bounds.Max.X; x++ {
				rgba64 := png.At(x, y).(color.RGBA64)
				fmt.Fprintf(w, "%04x%04x%04x ", rgba64.R, rgba64.G, rgba64.B)
			}
		case cm == color.NRGBAModel:
			for x := bounds.Min.X; x < bounds.Max.X; x++ {
				nrgba := png.At(x, y).(color.NRGBA)
				switch filename {
				case "ftbbn0g01", "ftbbn0g02", "ftbbn0g04":
					fmt.Fprintf(w, "%02x", nrgba.R)
				default:
					if useTransparent {
						fmt.Fprintf(w, "%02x%02x%02x ", nrgba.R, nrgba.G, nrgba.B)
					} else {
						fmt.Fprintf(w, "%02x%02x%02x%02x ", nrgba.R, nrgba.G, nrgba.B, nrgba.A)
					}
				}
			}
		case cm == color.NRGBA64Model:
			for x := bounds.Min.X; x < bounds.Max.X; x++ {
				nrgba64 := png.At(x, y).(color.NRGBA64)
				switch filename {
				case "ftbwn0g16":
					fmt.Fprintf(w, "%04x ", nrgba64.R)
				default:
					if useTransparent {
						fmt.Fprintf(w, "%04x%04x%04x ", nrgba64.R, nrgba64.G, nrgba64.B)
					} else {
						fmt.Fprintf(w, "%04x%04x%04x%04x ", nrgba64.R, nrgba64.G, nrgba64.B, nrgba64.A)
					}
				}
			}
		case cpm != nil:
			var b, c int
			for x := bounds.Min.X; x < bounds.Max.X; x++ {
				b = b<<uint(bitdepth) | int(paletted.ColorIndexAt(x, y))
				c++
				if c == 8/bitdepth {
					fmt.Fprintf(w, "%02x", b)
					b = 0
					c = 0
				}
			}
			if c != 0 {
				for c != 8/bitdepth {
					b = b << uint(bitdepth)
					c++
				}
				fmt.Fprintf(w, "%02x", b)
			}
		}
		io.WriteString(w, "\n")
	}
	io.WriteString(w, "}\n")
}

func NewSimulation(img *image.Paletted) *Simulation {
	size := img.Bounds().Size()
	groups := make(map[*group]struct{}, 0)
	matrix := newBucketMatrix(size.X, size.Y)
	for y := 0; y < size.Y; y++ {
		for x := 0; x < size.X; x++ {
			c := img.ColorIndexAt(x, y)
			if c > 0 && c <= maxCharge+1 {
				topLeftBucket := matrix.get(x-1, y-1)
				topBucket := matrix.get(x, y-1)
				leftBucket := matrix.get(x-1, y)
				var currentBucket *bucket
				switch {
				case nil == topBucket && nil == leftBucket:
					currentBucket = newBucket()
					groups[currentBucket.group] = struct{}{}
				case nil == topBucket && nil != leftBucket:
					currentBucket = leftBucket
				case (nil != topBucket && nil == leftBucket) ||
					topBucket == leftBucket ||
					topBucket.group == leftBucket.group:
					currentBucket = topBucket
				default:
					currentBucket = topBucket
					delete(groups, topBucket.group)
					topBucket.group.moveBucketsTo(leftBucket.group)
				}
				if nil != topLeftBucket && nil != topBucket && nil != leftBucket {
					currentBucket.group.wire.isPowerSource = true
				}
				matrix.set(x, y, currentBucket)
				currentBucket.addPixel(image.Point{x, y})
			}
		}
	}

	for y := 0; y < size.Y; y++ {
		for x := 0; x < size.X; x++ {
			if nil != matrix.get(x, y) {
				continue
			}
			topBucket := matrix.get(x, y-1)
			topRightBucket := matrix.get(x+1, y-1)
			rightBucket := matrix.get(x+1, y)
			bottomRightBucket := matrix.get(x+1, y+1)
			bottomBucket := matrix.get(x, y+1)
			bottomLeftBucket := matrix.get(x-1, y+1)
			leftBucket := matrix.get(x-1, y)
			topLeftBucket := matrix.get(x-1, y-1)
			if nil == topLeftBucket && nil == topRightBucket && nil == bottomLeftBucket && nil == bottomRightBucket &&
				nil != topBucket && nil != rightBucket && nil != bottomBucket && nil != leftBucket {
				delete(groups, topBucket.group)
				topBucket.group.moveBucketsTo(bottomBucket.group)
				delete(groups, leftBucket.group)
				leftBucket.group.moveBucketsTo(rightBucket.group)
			}
		}
	}

	transistors := make([]*transistor, 0)
	for y := 0; y < size.Y; y++ {
		for x := 0; x < size.X; x++ {
			if nil != matrix.get(x, y) {
				continue
			}
			topBucket := matrix.get(x, y-1)
			topRightBucket := matrix.get(x+1, y-1)
			rightBucket := matrix.get(x+1, y)
			bottomRightBucket := matrix.get(x+1, y+1)
			bottomBucket := matrix.get(x, y+1)
			bottomLeftBucket := matrix.get(x-1, y+1)
			leftBucket := matrix.get(x-1, y)
			topLeftBucket := matrix.get(x-1, y-1)

			switch {
			case nil == bottomLeftBucket && nil == bottomRightBucket &&
				nil == topBucket && nil != rightBucket && nil != bottomBucket && nil != leftBucket:
				transistors = append(transistors,
					newTransistor(image.Point{x, y}, bottomBucket.group.wire, rightBucket.group.wire, leftBucket.group.wire))
			case nil == bottomLeftBucket && nil == topLeftBucket &&
				nil != topBucket && nil == rightBucket && nil != bottomBucket && nil != leftBucket:
				transistors = append(transistors,
					newTransistor(image.Point{x, y}, leftBucket.group.wire, topBucket.group.wire, bottomBucket.group.wire))
			case nil == topLeftBucket && nil == topRightBucket &&
				nil != topBucket && nil != rightBucket && nil == bottomBucket && nil != leftBucket:
				transistors = append(transistors,
					newTransistor(image.Point{x, y}, topBucket.group.wire, rightBucket.group.wire, leftBucket.group.wire))
			case nil == bottomRightBucket && nil == topRightBucket &&
				nil != topBucket && nil != rightBucket && nil != bottomBucket && nil == leftBucket:
				transistors = append(transistors,
					newTransistor(image.Point{x, y}, rightBucket.group.wire, topBucket.group.wire, bottomBucket.group.wire))
			}
		}
	}

	wires := make([]*wire, len(groups))
	wireStates := make([]wireState, len(groups))
	i := 0
	for k := range groups {
		k.wire.index = i
//.........這裏部分代碼省略.........

// An approximation of the sng command-line tool.
func sng(w io.WriteCloser, filename string, png image.Image) {
	defer w.Close()
	bounds := png.Bounds()
	cm := png.ColorModel()
	var bitdepth int
	switch cm {
	case image.RGBAColorModel, image.NRGBAColorModel, image.AlphaColorModel, image.GrayColorModel:
		bitdepth = 8
	default:
		bitdepth = 16
	}
	cpm, _ := cm.(image.PalettedColorModel)
	var paletted *image.Paletted
	if cpm != nil {
		bitdepth = 8
		paletted = png.(*image.Paletted)
	}

	// Write the filename and IHDR.
	io.WriteString(w, "#SNG: from "+filename+".png\nIHDR {\n")
	fmt.Fprintf(w, "    width: %d; height: %d; bitdepth: %d;\n", bounds.Dx(), bounds.Dy(), bitdepth)
	switch {
	case cm == image.RGBAColorModel, cm == image.RGBA64ColorModel:
		io.WriteString(w, "    using color;\n")
	case cm == image.NRGBAColorModel, cm == image.NRGBA64ColorModel:
		io.WriteString(w, "    using color alpha;\n")
	case cm == image.GrayColorModel, cm == image.Gray16ColorModel:
		io.WriteString(w, "    using grayscale;\n")
	case cpm != nil:
		io.WriteString(w, "    using color palette;\n")
	default:
		io.WriteString(w, "unknown PNG decoder color model\n")
	}
	io.WriteString(w, "}\n")

	// We fake a gAMA output. The test files have a gAMA chunk but the go PNG parser ignores it
	// (the PNG spec section 11.3 says "Ancillary chunks may be ignored by a decoder").
	io.WriteString(w, "gAMA {1.0000}\n")

	// Write the PLTE (if applicable).
	if cpm != nil {
		io.WriteString(w, "PLTE {\n")
		for i := 0; i < len(cpm); i++ {
			r, g, b, _ := cpm[i].RGBA()
			r >>= 8
			g >>= 8
			b >>= 8
			fmt.Fprintf(w, "    (%3d,%3d,%3d)     # rgb = (0x%02x,0x%02x,0x%02x)\n", r, g, b, r, g, b)
		}
		io.WriteString(w, "}\n")
	}

	// Write the IMAGE.
	io.WriteString(w, "IMAGE {\n    pixels hex\n")
	for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
		switch {
		case cm == image.GrayColorModel:
			for x := bounds.Min.X; x < bounds.Max.X; x++ {
				gray := png.At(x, y).(image.GrayColor)
				fmt.Fprintf(w, "%02x", gray.Y)
			}
		case cm == image.Gray16ColorModel:
			for x := bounds.Min.X; x < bounds.Max.X; x++ {
				gray16 := png.At(x, y).(image.Gray16Color)
				fmt.Fprintf(w, "%04x ", gray16.Y)
			}
		case cm == image.RGBAColorModel:
			for x := bounds.Min.X; x < bounds.Max.X; x++ {
				rgba := png.At(x, y).(image.RGBAColor)
				fmt.Fprintf(w, "%02x%02x%02x ", rgba.R, rgba.G, rgba.B)
			}
		case cm == image.RGBA64ColorModel:
			for x := bounds.Min.X; x < bounds.Max.X; x++ {
				rgba64 := png.At(x, y).(image.RGBA64Color)
				fmt.Fprintf(w, "%04x%04x%04x ", rgba64.R, rgba64.G, rgba64.B)
			}
		case cm == image.NRGBAColorModel:
			for x := bounds.Min.X; x < bounds.Max.X; x++ {
				nrgba := png.At(x, y).(image.NRGBAColor)
				fmt.Fprintf(w, "%02x%02x%02x%02x ", nrgba.R, nrgba.G, nrgba.B, nrgba.A)
			}
		case cm == image.NRGBA64ColorModel:
			for x := bounds.Min.X; x < bounds.Max.X; x++ {
				nrgba64 := png.At(x, y).(image.NRGBA64Color)
				fmt.Fprintf(w, "%04x%04x%04x%04x ", nrgba64.R, nrgba64.G, nrgba64.B, nrgba64.A)
			}
		case cpm != nil:
			for x := bounds.Min.X; x < bounds.Max.X; x++ {
				fmt.Fprintf(w, "%02x", paletted.ColorIndexAt(x, y))
			}
		}
		io.WriteString(w, "\n")
	}
	io.WriteString(w, "}\n")
}

// An approximation of the sng command-line tool.
func sng(w io.WriteCloser, filename string, png image.Image) {
	defer w.Close()
	// For now, the go PNG parser only reads bitdepths of 8.
	bitdepth := 8

	// Write the filename and IHDR.
	io.WriteString(w, "#SNG: from "+filename+".png\nIHDR {\n")
	fmt.Fprintf(w, "    width: %d; height: %d; bitdepth: %d;\n", png.Width(), png.Height(), bitdepth)
	cm := png.ColorModel()
	var paletted *image.Paletted
	cpm, _ := cm.(image.PalettedColorModel)
	switch {
	case cm == image.RGBAColorModel:
		io.WriteString(w, "    using color;\n")
	case cm == image.NRGBAColorModel:
		io.WriteString(w, "    using color alpha;\n")
	case cpm != nil:
		io.WriteString(w, "    using color palette;\n")
		paletted = png.(*image.Paletted)
	default:
		io.WriteString(w, "unknown PNG decoder color model\n")
	}
	io.WriteString(w, "}\n")

	// We fake a gAMA output. The test files have a gAMA chunk but the go PNG parser ignores it
	// (the PNG spec section 11.3 says "Ancillary chunks may be ignored by a decoder").
	io.WriteString(w, "gAMA {1.0000}\n")

	// Write the PLTE (if applicable).
	if cpm != nil {
		io.WriteString(w, "PLTE {\n")
		for i := 0; i < len(cpm); i++ {
			r, g, b, _ := cpm[i].RGBA()
			r >>= 24
			g >>= 24
			b >>= 24
			fmt.Fprintf(w, "    (%3d,%3d,%3d)     # rgb = (0x%02x,0x%02x,0x%02x)\n", r, g, b, r, g, b)
		}
		io.WriteString(w, "}\n")
	}

	// Write the IMAGE.
	io.WriteString(w, "IMAGE {\n    pixels hex\n")
	for y := 0; y < png.Height(); y++ {
		switch {
		case cm == image.RGBAColorModel:
			for x := 0; x < png.Width(); x++ {
				rgba := png.At(x, y).(image.RGBAColor)
				fmt.Fprintf(w, "%02x%02x%02x ", rgba.R, rgba.G, rgba.B)
			}
		case cm == image.NRGBAColorModel:
			for x := 0; x < png.Width(); x++ {
				nrgba := png.At(x, y).(image.NRGBAColor)
				fmt.Fprintf(w, "%02x%02x%02x%02x ", nrgba.R, nrgba.G, nrgba.B, nrgba.A)
			}
		case cpm != nil:
			for x := 0; x < png.Width(); x++ {
				fmt.Fprintf(w, "%02x", paletted.ColorIndexAt(x, y))
			}
		}
		io.WriteString(w, "\n")
	}
	io.WriteString(w, "}\n")
}