Add named colors (e.g. image.Blue), suitable for exp/draw.

R=r, rsc
CC=golang-dev
https://golang.org/cl/198066

src/pkg/image/Makefile

@@ -8,5 +8,6 @@ TARG=image
 GOFILES=\
 	color.go\
 	image.go\
+	names.go\
 
 include ../../Make.pkg

src/pkg/image/names.go

+// Copyright 2010 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 image
+
+// Colors from the HTML 4.01 specification: http://www.w3.org/TR/REC-html40/types.html#h-6.5
+// These names do not necessarily match those from other lists, such as the X11 color names.
+var (
+	Aqua    = ColorImage{RGBAColor{0x00, 0xff, 0xff, 0xff}}
+	Black   = ColorImage{RGBAColor{0x00, 0x00, 0x00, 0xff}}
+	Blue    = ColorImage{RGBAColor{0x00, 0x00, 0xff, 0xff}}
+	Fuchsia = ColorImage{RGBAColor{0xff, 0x00, 0xff, 0xff}}
+	Gray    = ColorImage{RGBAColor{0x80, 0x80, 0x80, 0xff}}
+	Green   = ColorImage{RGBAColor{0x00, 0x80, 0x00, 0xff}}
+	Lime    = ColorImage{RGBAColor{0x00, 0xff, 0x00, 0xff}}
+	Maroon  = ColorImage{RGBAColor{0x80, 0x00, 0x00, 0xff}}
+	Navy    = ColorImage{RGBAColor{0x00, 0x00, 0x80, 0xff}}
+	Olive   = ColorImage{RGBAColor{0x80, 0x80, 0x00, 0xff}}
+	Red     = ColorImage{RGBAColor{0xff, 0x00, 0x00, 0xff}}
+	Purple  = ColorImage{RGBAColor{0x80, 0x00, 0x80, 0xff}}
+	Silver  = ColorImage{RGBAColor{0xc0, 0xc0, 0xc0, 0xff}}
+	Teal    = ColorImage{RGBAColor{0x00, 0x80, 0x80, 0xff}}
+	White   = ColorImage{RGBAColor{0xff, 0xff, 0xff, 0xff}}
+	Yellow  = ColorImage{RGBAColor{0xff, 0xff, 0x00, 0xff}}
+
+	// These synonyms are not in HTML 4.01.
+	Cyan    = Aqua
+	Magenta = Fuchsia
+)
+
+// A ColorImage is a practically infinite-sized Image of uniform Color.
+// It implements both the Color and Image interfaces.
+type ColorImage struct {
+	C Color
+}
+
+func (c ColorImage) RGBA() (r, g, b, a uint32) {
+	return c.C.RGBA()
+}
+
+func (c ColorImage) ColorModel() ColorModel {
+	return ColorModelFunc(func(Color) Color { return c.C })
+}
+
+func (c ColorImage) Width() int { return 1e9 }
+
+func (c ColorImage) Height() int { return 1e9 }
+
+func (c ColorImage) At(x, y int) Color { return c.C }