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// Package sixel can be used to render image.Image to the terminal using
// various strategies (including sixel).
package sixel
import (
"bufio"
"fmt"
"image"
"image/color"
"image/color/palette"
"image/draw"
"io"
"maps"
"slices"
)
func scale100(c uint32) int {
return int(c) * 100 / 0xffff
}
var sixelPalette = append(color.Palette{color.Transparent}, palette.WebSafe...)
// Print renders the given image as a sixel.
func Print(w io.Writer, img image.Image) error {
palettized := image.NewPaletted(img.Bounds(), sixelPalette)
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 sixelPalette[1:] {
r, g, b, _ := c.RGBA()
if _, err := fmt.Fprintf(bw, "#%d;2;%d;%d;%d", i, scale100(r), scale100(g), scale100(b)); err != nil {
return err
}
}
for row := 0; row < palettized.Bounds().Dy(); row += 6 {
y0 := palettized.Bounds().Min.Y + row
if row > 0 {
if _, err := bw.WriteString("-"); err != nil {
return err
}
}
colors := make(map[uint8]bool)
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
}
}
}
if len(colors) == 0 {
if _, err := fmt.Fprintf(bw, "!%d?", palettized.Bounds().Dx()); err != nil {
return err
}
}
for i, c := range slices.Sorted(maps.Keys(colors)) {
if i > 0 {
if _, err := bw.WriteString("$"); err != nil {
return err
}
}
if _, err := fmt.Fprintf(bw, "#%d", c-1); err != nil {
return err
}
var (
lastChar byte
lastCharLen int
)
for x := palettized.Bounds().Min.X; x < palettized.Bounds().Max.X; x++ {
var char byte
for j := range 6 {
y := y0 + j
if palettized.ColorIndexAt(x, y) == c {
char |= 1 << j
}
}
char += '?'
if lastCharLen > 0 && lastChar != char {
if lastCharLen < 4 {
for range lastCharLen {
if err := bw.WriteByte(lastChar); err != nil {
return err
}
}
} else {
if _, err := fmt.Fprintf(bw, "!%d%c", lastCharLen, lastChar); err != nil {
return err
}
}
lastCharLen = 0
}
lastChar = char
lastCharLen++
}
if lastCharLen > 0 {
if lastCharLen < 4 {
for range lastCharLen {
if err := bw.WriteByte(lastChar); err != nil {
return err
}
}
} else {
if _, err := fmt.Fprintf(bw, "!%d%c", lastCharLen, lastChar); err != nil {
return err
}
}
}
}
}
if _, err := bw.WriteString("\033\\"); err != nil {
return err
}
if err := bw.Flush(); err != nil {
return err
}
return nil
}
func isFullyTransparent(c color.Color) bool {
_, _, _, a := c.RGBA()
return a == 0
}
// PrintBlock renders the given image using block characters. Yeah I know it's
// not a sixel but it could be used as a fallback if sixel isn't supported.
func PrintBlock(w io.Writer, img image.Image) error {
bw := bufio.NewWriter(w)
for row := 0; row < img.Bounds().Dy(); row += 2 {
y := img.Bounds().Min.Y + row
if row > 0 {
if _, err := bw.WriteString("\n"); err != nil {
return err
}
}
for x := img.Bounds().Min.X; x < img.Bounds().Max.X; x++ {
hi := img.At(x, y)
if isFullyTransparent(hi) {
if y+1 >= img.Bounds().Max.Y || isFullyTransparent(img.At(x, y+1)) {
if _, err := bw.WriteString("\033[49m "); err != nil {
return err
}
} else {
r, g, b, _ := img.At(x, y+1).RGBA()
if _, err := fmt.Fprintf(bw, "\033[38;2;%d;%d;%dm\033[49m▄", r>>8, g>>8, b>>8); err != nil {
return err
}
}
} else {
if y+1 < img.Bounds().Max.Y && !isFullyTransparent(img.At(x, y+1)) {
r, g, b, _ := img.At(x, y+1).RGBA()
if _, err := fmt.Fprintf(bw, "\033[48;2;%d;%d;%dm", r>>8, g>>8, b>>8); err != nil {
return err
}
} else {
if _, err := bw.WriteString("\033[49m"); err != nil {
return err
}
}
r, g, b, _ := hi.RGBA()
if _, err := fmt.Fprintf(bw, "\033[38;2;%d;%d;%dm▀", r>>8, g>>8, b>>8); err != nil {
return err
}
}
}
if _, err := bw.WriteString("\033[39m\033[49m"); err != nil {
return err
}
}
if err := bw.Flush(); err != nil {
return err
}
return nil
}
type xtermColor int8
func (c xtermColor) RGBA() (r, g, b, a uint32) {
var col color.RGBA
switch c {
case 0:
col = color.RGBA{R: 0x00, G: 0x00, B: 0x00, A: 0xff}
case 1:
col = color.RGBA{R: 0xcd, G: 0x00, B: 0x00, A: 0xff}
case 2:
col = color.RGBA{R: 0x00, G: 0xcd, B: 0x00, A: 0xff}
case 3:
col = color.RGBA{R: 0xcd, G: 0xcd, B: 0x00, A: 0xff}
case 4:
col = color.RGBA{R: 0x00, G: 0x00, B: 0xee, A: 0xff}
case 5:
col = color.RGBA{R: 0xcd, G: 0x00, B: 0xcd, A: 0xff}
case 6:
col = color.RGBA{R: 0x00, G: 0xcd, B: 0xcd, A: 0xff}
case 7:
col = color.RGBA{R: 0xe5, G: 0xe5, B: 0xe5, A: 0xff}
case 60:
col = color.RGBA{R: 0x7f, G: 0x7f, B: 0x7f, A: 0xff}
case 61:
col = color.RGBA{R: 0xff, G: 0x00, B: 0x00, A: 0xff}
case 62:
col = color.RGBA{R: 0x00, G: 0xff, B: 0x00, A: 0xff}
case 63:
col = color.RGBA{R: 0xff, G: 0xff, B: 0x00, A: 0xff}
case 64:
col = color.RGBA{R: 0x5c, G: 0x5c, B: 0xff, A: 0xff}
case 65:
col = color.RGBA{R: 0xff, G: 0x00, B: 0xff, A: 0xff}
case 66:
col = color.RGBA{R: 0x00, G: 0xff, B: 0xff, A: 0xff}
case 67:
col = color.RGBA{R: 0xff, G: 0xff, B: 0xff, A: 0xff}
default:
panic("not an xterm color")
}
return col.RGBA()
}
var xtermPalette = color.Palette{color.Transparent, xtermColor(0), xtermColor(1), xtermColor(2), xtermColor(3), xtermColor(4), xtermColor(5), xtermColor(6), xtermColor(7), xtermColor(60), xtermColor(61), xtermColor(62), xtermColor(63), xtermColor(64), xtermColor(65), xtermColor(66), xtermColor(67)}
// PrintXterm16 renders the given image using the basic XTerm 16 colors. This
// should have great compatibility and it looks pretty impressively bad.
func PrintXTerm16(w io.Writer, img image.Image) error {
palettized := image.NewPaletted(img.Bounds(), xtermPalette)
draw.FloydSteinberg.Draw(palettized, palettized.Bounds(), img, image.Point{})
bw := bufio.NewWriter(w)
for row := 0; row < palettized.Bounds().Dy(); row++ {
y := palettized.Bounds().Min.Y + row
if row > 0 {
if _, err := bw.WriteString("\n"); err != nil {
return err
}
}
for x := palettized.Bounds().Min.X; x < palettized.Bounds().Max.X; x++ {
c := palettized.At(x, y)
if c == color.Transparent {
if _, err := bw.WriteString("\033[49m "); err != nil {
return err
}
} else {
if _, err := fmt.Fprintf(bw, "\033[%dm ", 40+c.(xtermColor)); err != nil {
return err
}
}
}
if _, err := bw.WriteString("\033[49m"); err != nil {
return err
}
}
if err := bw.Flush(); err != nil {
return err
}
return nil
}
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