Initial commit

1 files changed, 205 insertions, 0 deletions

diff --git a/sixel.go b/sixel.go
new file mode 100644
index 0000000..4e44c79
--- /dev/null
+++ b/sixel.go
@@ -0,0 +1,205 @@
+// 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"
+)
+
+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 := io.WriteString(bw, "\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++ {
+		y := palettized.Bounds().Min.Y + row
+		if row > 0 {
+			if row%6 == 0 {
+				if _, err := io.WriteString(bw, "-"); err != nil {
+					return err
+				}
+			} else {
+				if _, err := io.WriteString(bw, "$"); err != nil {
+					return err
+				}
+			}
+		}
+		for x := palettized.Bounds().Min.X; x < palettized.Bounds().Max.X; x++ {
+			c := palettized.ColorIndexAt(x, y)
+			if c == 0 {
+				if _, err := fmt.Fprint(bw, "?"); err != nil {
+					return err
+				}
+			} else {
+				char := '?' + 1<<(row%6)
+				if _, err := fmt.Fprintf(bw, "#%d%c", c-1, char); err != nil {
+					return err
+				}
+			}
+		}
+	}
+	if _, err := io.WriteString(bw, "\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 := io.WriteString(bw, "\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 := io.WriteString(bw, "\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 := io.WriteString(bw, "\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 := io.WriteString(bw, "\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 := io.WriteString(bw, "\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 := io.WriteString(bw, "\033[49m "); err != nil {
+					return err
+				}
+			} else {
+				if _, err := fmt.Fprintf(bw, "\033[%dm ", 40+c.(xtermColor)); err != nil {
+					return err
+				}
+			}
+		}
+		if _, err := io.WriteString(bw, "\033[49m"); err != nil {
+			return err
+		}
+	}
+	if err := bw.Flush(); err != nil {
+		return err
+	}
+	return nil
+}