src/pkg/exp/draw/color.go

// Copyright 2009 The Go Authors.  All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package draw

import "image"

// A Color represents a color with 8-bit R, G, B, and A values,
// packed into a uint32—0xRRGGBBAA—so that comparison
// is defined on colors.
// Color implements image.Color.
// Color also implements image.Image: it is a
// 10⁹x10⁹-pixel image of uniform color.
type Color uint32

// Check that Color implements image.Color and image.Image
var _ image.Color = Black
var _ image.Image = Black

var (
	Opaque		Color	= 0xFFFFFFFF;
	Transparent	Color	= 0x00000000;
	Black		Color	= 0x000000FF;
	White		Color	= 0xFFFFFFFF;
	Red		Color	= 0xFF0000FF;
	Green		Color	= 0x00FF00FF;
	Blue		Color	= 0x0000FFFF;
	Cyan		Color	= 0x00FFFFFF;
	Magenta		Color	= 0xFF00FFFF;
	Yellow		Color	= 0xFFFF00FF;
	PaleYellow	Color	= 0xFFFFAAFF;
	DarkYellow	Color	= 0xEEEE9EFF;
	DarkGreen	Color	= 0x448844FF;
	PaleGreen	Color	= 0xAAFFAAFF;
	MedGreen	Color	= 0x88CC88FF;
	DarkBlue	Color	= 0x000055FF;
	PaleBlueGreen	Color	= 0xAAFFFFFF;
	PaleBlue	Color	= 0x0000BBFF;
	BlueGreen	Color	= 0x008888FF;
	GreyGreen	Color	= 0x55AAAAFF;
	PaleGreyGreen	Color	= 0x9EEEEEFF;
	YellowGreen	Color	= 0x99994CFF;
	MedBlue		Color	= 0x000099FF;
	GreyBlue	Color	= 0x005DBBFF;
	PaleGreyBlue	Color	= 0x4993DDFF;
	PurpleBlue	Color	= 0x8888CCFF;
)

func (c Color) RGBA() (r, g, b, a uint32) {
	x := uint32(c);
	r, g, b, a = x>>24, (x>>16)&0xFF, (x>>8)&0xFF, x&0xFF;
	r |= r << 8;
	r |= r << 16;
	g |= g << 8;
	g |= g << 16;
	b |= b << 8;
	b |= b << 16;
	a |= a << 8;
	a |= a << 16;
	return;
}

// SetAlpha returns the color obtained by changing
// c's alpha value to a and scaling r, g, and b appropriately.
func (c Color) SetAlpha(a uint8) Color {
	r, g, b, oa := c>>24, (c>>16)&0xFF, (c>>8)&0xFF, c&0xFF;
	if oa == 0 {
		return 0
	}
	r = r * Color(a) / oa;
	if r < 0 {
		r = 0
	}
	if r > 0xFF {
		r = 0xFF
	}
	g = g * Color(a) / oa;
	if g < 0 {
		g = 0
	}
	if g > 0xFF {
		g = 0xFF
	}
	b = b * Color(a) / oa;
	if b < 0 {
		b = 0
	}
	if b > 0xFF {
		b = 0xFF
	}
	return r<<24 | g<<16 | b<<8 | Color(a);
}

func (c Color) Width() int	{ return 1e9 }

func (c Color) Height() int	{ return 1e9 }

func (c Color) At(x, y int) image.Color	{ return c }

func toColor(color image.Color) image.Color {
	if c, ok := color.(Color); ok {
		return c
	}
	r, g, b, a := color.RGBA();
	return Color(r>>24<<24 | g>>24<<16 | b>>24<<8 | a>>24);
}

func (c Color) ColorModel() image.ColorModel	{ return image.ColorModelFunc(toColor) }