Start work on transmitting RGB images

tools/utils/images/to_rgb.go

@@ -0,0 +1,141 @@
+// License: GPLv3 Copyright: 2023, Kovid Goyal, <kovid at kovidgoyal.net>
+
+package images
+
+import (
+	"fmt"
+	"image"
+	"image/color"
+)
+
+var _ = fmt.Print
+
+type NRGBColor struct {
+	R, G, B uint8
+}
+
+func (c NRGBColor) RGBA() (r, g, b, a uint32) {
+	r = uint32(c.R)
+	r |= r << 8
+	g = uint32(c.G)
+	g |= g << 8
+	b = uint32(c.B)
+	b |= b << 8
+	a = 65280 // ( 255 << 8 )
+	return
+}
+
+// NRGB is an in-memory image whose At method returns NRGBColor values.
+type NRGB struct {
+	// Pix holds the image's pixels, in R, G, B, A order. The pixel at
+	// (x, y) starts at Pix[(y-Rect.Min.Y)*Stride + (x-Rect.Min.X)*4].
+	Pix []uint8
+	// Stride is the Pix stride (in bytes) between vertically adjacent pixels.
+	Stride int
+	// Rect is the image's bounds.
+	Rect image.Rectangle
+}
+
+func nrgbModel(c color.Color) color.Color {
+	if _, ok := c.(NRGBColor); ok {
+		return c
+	}
+	r, g, b, a := c.RGBA()
+	if a == 0xffff {
+		return NRGBColor{uint8(r >> 8), uint8(g >> 8), uint8(b >> 8)}
+	}
+	if a == 0 {
+		return NRGBColor{0, 0, 0}
+	}
+	// Since Color.RGBA returns an alpha-premultiplied color, we should have r <= a && g <= a && b <= a.
+	r = (r * 0xffff) / a
+	g = (g * 0xffff) / a
+	b = (b * 0xffff) / a
+	return NRGBColor{uint8(r >> 8), uint8(g >> 8), uint8(b >> 8)}
+}
+
+var NRGBModel color.Model = color.ModelFunc(nrgbModel)
+
+func (p *NRGB) ColorModel() color.Model { return NRGBModel }
+
+func (p *NRGB) Bounds() image.Rectangle { return p.Rect }
+
+func (p *NRGB) At(x, y int) color.Color {
+	return p.NRGBAt(x, y)
+}
+
+func (p *NRGB) NRGBAt(x, y int) NRGBColor {
+	if !(image.Point{x, y}.In(p.Rect)) {
+		return NRGBColor{}
+	}
+	i := p.PixOffset(x, y)
+	s := p.Pix[i : i+4 : i+4] // Small cap improves performance, see https://golang.org/issue/27857
+	return NRGBColor{s[0], s[1], s[2]}
+}
+
+// PixOffset returns the index of the first element of Pix that corresponds to
+// the pixel at (x, y).
+func (p *NRGB) PixOffset(x, y int) int {
+	return (y-p.Rect.Min.Y)*p.Stride + (x-p.Rect.Min.X)*4
+}
+
+func (p *NRGB) Set(x, y int, c color.Color) {
+	if !(image.Point{x, y}.In(p.Rect)) {
+		return
+	}
+	i := p.PixOffset(x, y)
+	c1 := NRGBModel.Convert(c).(NRGBColor)
+	s := p.Pix[i : i+3 : i+3] // Small cap improves performance, see https://golang.org/issue/27857
+	s[0] = c1.R
+	s[1] = c1.G
+	s[2] = c1.B
+}
+
+func (p *NRGB) SetRGBA64(x, y int, c color.RGBA64) {
+	if !(image.Point{x, y}.In(p.Rect)) {
+		return
+	}
+	r, g, b, a := uint32(c.R), uint32(c.G), uint32(c.B), uint32(c.A)
+	if (a != 0) && (a != 0xffff) {
+		r = (r * 0xffff) / a
+		g = (g * 0xffff) / a
+		b = (b * 0xffff) / a
+	}
+	i := p.PixOffset(x, y)
+	s := p.Pix[i : i+3 : i+3] // Small cap improves performance, see https://golang.org/issue/27857
+	s[0] = uint8(r >> 8)
+	s[1] = uint8(g >> 8)
+	s[2] = uint8(b >> 8)
+}
+
+func (p *NRGB) SetNRGBA(x, y int, c color.NRGBA) {
+	if !(image.Point{x, y}.In(p.Rect)) {
+		return
+	}
+	i := p.PixOffset(x, y)
+	s := p.Pix[i : i+3 : i+3] // Small cap improves performance, see https://golang.org/issue/27857
+	s[0] = c.R
+	s[1] = c.G
+	s[2] = c.B
+}
+
+// SubImage returns an image representing the portion of the image p visible
+// through r. The returned value shares pixels with the original image.
+func (p *NRGB) SubImage(r image.Rectangle) image.Image {
+	r = r.Intersect(p.Rect)
+	// If r1 and r2 are Rectangles, r1.Intersect(r2) is not guaranteed to be inside
+	// either r1 or r2 if the intersection is empty. Without explicitly checking for
+	// this, the Pix[i:] expression below can panic.
+	if r.Empty() {
+		return &NRGB{}
+	}
+	i := p.PixOffset(r.Min.X, r.Min.Y)
+	return &NRGB{
+		Pix:    p.Pix[i:],
+		Stride: p.Stride,
+		Rect:   r,
+	}
+}
+
+// Opaque scans the entire image and reports whether it is fully opaque.
+func (p *NRGB) Opaque() bool { return true }