diff options
| -rw-r--r-- | sixel.go | 184 |
1 files changed, 46 insertions, 138 deletions
@@ -7,164 +7,65 @@ import ( "fmt" "image" "image/color" + "image/color/palette" "image/draw" "io" - "maps" - "math" - "math/rand/v2" "slices" ) -func scale100(c int64) int8 { - return int8(c * 100 / 0xff) -} - -func scaleFFFF(c int8) uint32 { - return uint32(c) * 0xffff / 100 -} - type sixelRGB struct { r, g, b int8 } func (c sixelRGB) RGBA() (r, g, b, a uint32) { - return scaleFFFF(c.r), scaleFFFF(c.g), scaleFFFF(c.b), 0xffff + return uint32(c.r) * 0xffff / 100, uint32(c.g) * 0xffff / 100, uint32(c.b) * 0xffff / 100, 0xffff } -func partition[S ~[]E, E any](a S, i, j, pivotIndex int, cmp func(E, E) int) int { - pivot := a[pivotIndex] - for { - for ; cmp(a[i], pivot) < 0; i++ { - } - for ; cmp(a[j], pivot) > 0; j-- { - } - if i >= j { - return j - } - a[i], a[j] = a[j], a[i] - i++ - j-- - } -} +var defaultSixelPalette color.Palette -func quickSelect[S ~[]E, E any](list S, k int, cmp func(E, E) int) { - left, right := 0, len(list)-1 - for { - if left == right { - return - } - pivotIndex := left + rand.IntN(right-left+1) - pivotIndex = partition(list, left, right, pivotIndex, cmp) - if k <= pivotIndex { - right = pivotIndex - } else { - left = pivotIndex + 1 - } +func init() { + defaultSixelPalette = slices.Grow(color.Palette{color.Transparent}, len(palette.WebSafe)) + for _, c := range palette.WebSafe { + r, g, b, _ := c.RGBA() + defaultSixelPalette = append(defaultSixelPalette, sixelRGB{int8(r * 100 / 0xffff), int8(g * 100 / 0xffff), int8(b * 100 / 0xffff)}) } } -func bucketRange(colors []color.RGBA) color.RGBA { - if len(colors) == 0 { - return color.RGBA{} +func sixelizePalette(p color.Palette) color.Palette { + var result color.Palette + includeTransparent := false + for _, c := range p { + r, g, b, a := c.RGBA() + if a == 0 { + includeTransparent = true + continue + } + result = append(result, sixelRGB{r: int8(r * 100 / 0xffff), g: int8(g * 100 / 0xffff), b: int8(b * 100 / 0xffff)}) } - var minR, minG, minB uint8 = math.MaxUint8, math.MaxUint8, math.MaxUint8 - var maxR, maxG, maxB uint8 - for _, c := range colors { - minR, maxR = min(minR, c.R), max(maxR, c.R) - minG, maxG = min(minG, c.G), max(maxG, c.G) - minB, maxB = min(minB, c.B), max(maxB, c.B) + if includeTransparent { + result = append(color.Palette{color.Transparent}, result...) } - return color.RGBA{R: maxR - minR, G: maxG - minG, B: maxB - minB} + return result } -func cutOnce(colors []color.RGBA, bucketRange color.RGBA) [2][]color.RGBA { - if len(colors) == 0 { - return [...][]color.RGBA{colors, colors} - } - rRange, gRange, bRange := bucketRange.R, bucketRange.G, bucketRange.B - if rRange >= gRange && rRange >= bRange { - quickSelect(colors, len(colors)/2, func(x, y color.RGBA) int { return int(x.R) - int(y.R) }) - } else if gRange >= rRange && gRange >= bRange { - quickSelect(colors, len(colors)/2, func(x, y color.RGBA) int { return int(x.G) - int(y.G) }) +// Print renders the given image as a sixel. The given palette will be used if +// provided, otherwise a default palette will be selected. +func Print(w io.Writer, img image.Image, p color.Palette) error { + if len(p) == 0 { + p = defaultSixelPalette } else { - quickSelect(colors, len(colors)/2, func(x, y color.RGBA) int { return int(x.B) - int(y.B) }) + p = sixelizePalette(p) } - return [...][]color.RGBA{colors[:len(colors)/2], colors[len(colors)/2:]} -} - -func colorAvg(colors []color.RGBA) sixelRGB { - var r, g, b int64 - for _, c := range colors { - r += int64(c.R) - g += int64(c.G) - b += int64(c.B) - } - n := int64(len(colors)) - return sixelRGB{r: scale100(r / n), g: scale100(g / n), b: scale100(b / n)} -} - -func medianCut(img image.Image) color.Palette { - var colors []color.RGBA - for y := img.Bounds().Min.Y; y < img.Bounds().Max.Y; y++ { - for x := img.Bounds().Min.X; x < img.Bounds().Max.X; x++ { - r, g, b, a := img.At(x, y).RGBA() - if a > 0 { - colors = append(colors, color.RGBA{R: uint8(r >> 8), G: uint8(g >> 8), B: uint8(b >> 8), A: 0xff}) - } - } - } - buckets := [][]color.RGBA{colors} - bucketRanges := []color.RGBA{{}} - for { - var bestRange uint8 - var bestIdx int - for i, rng := range bucketRanges { - r := max(rng.R, rng.G, rng.B) - if r >= bestRange { - bestRange = r - bestIdx = i - } - } - split := cutOnce(buckets[bestIdx], bucketRanges[bestIdx]) - buckets = slices.Replace(buckets, bestIdx, bestIdx+1, split[:]...) - if len(buckets) == 255 { - break - } - bucketRanges = slices.Replace(bucketRanges, bestIdx, bestIdx+1, bucketRange(split[0]), bucketRange(split[1])) - } - var paletteRGB []sixelRGB - for _, bucket := range buckets { - if len(bucket) > 0 { - paletteRGB = append(paletteRGB, colorAvg(bucket)) - } - } - slices.SortFunc(paletteRGB, func(x, y sixelRGB) int { - if n := int(x.r) - int(y.r); n != 0 { - return n - } - if n := int(x.g) - int(y.g); n != 0 { - return n - } - return int(x.b) - int(y.b) - }) - paletteRGB = slices.Compact(paletteRGB) - palette := slices.Grow(color.Palette{color.Transparent}, len(paletteRGB)) - for _, c := range paletteRGB { - palette = append(palette, c) - } - return palette -} - -// Print renders the given image as a sixel. -func Print(w io.Writer, img image.Image) error { - palette := medianCut(img) - palettized := image.NewPaletted(img.Bounds(), palette) + palettized := image.NewPaletted(img.Bounds(), p) draw.FloydSteinberg.Draw(palettized, palettized.Bounds(), img, image.Point{}) bw := bufio.NewWriter(w) if _, err := bw.WriteString("\033P7;1q"); err != nil { return err } - for i, c := range palette[1:] { + for i, c := range palettized.ColorModel().(color.Palette) { + if c == color.Transparent { + continue + } sc := c.(sixelRGB) if _, err := fmt.Fprintf(bw, "#%d;2;%d;%d;%d", i, sc.r, sc.g, sc.b); err != nil { return err @@ -177,22 +78,29 @@ func Print(w io.Writer, img image.Image) error { return err } } - colors := make(map[uint8]bool) + colors := make([]bool, 256) for y := y0; y < y0+6; y++ { for x := palettized.Bounds().Min.X; x < palettized.Bounds().Max.X; x++ { - if c := palettized.ColorIndexAt(x, y); c != 0 { - colors[c] = true - } + colors[palettized.ColorIndexAt(x, y)] = true } } + if p[0] == color.Transparent { + colors[0] = false + } - for i, c := range slices.Sorted(maps.Keys(colors)) { - if i > 0 { + first := true + for ci, present := range colors { + c := uint8(ci) + if !present { + continue + } + if !first { if _, err := bw.WriteString("$"); err != nil { return err } } - if _, err := fmt.Fprintf(bw, "#%d", c-1); err != nil { + first = false + if _, err := fmt.Fprintf(bw, "#%d", c); err != nil { return err } var ( |