image/color/palette: move Plan9Palette and WebSafePalette out of the

image/color package into their own package. They require some non-
trivial init-time code (interface conversions, currently 40KiB of text)
that would otherwise burden any Go program that imported image/color.

R=r
CC=golang-dev
https://golang.org/cl/13256046

src/pkg/image/color/gen.go → src/pkg/image/color/palette/gen.go

@@ -7,7 +7,7 @@
 package main
 
 // This program generates palette.go. Invoke it as
-//	go run gen.go |gofmt >palette.go
+//	go run gen.go | gofmt > palette.go
 
 import (
 	"fmt"
@@ -16,7 +16,10 @@ import (
 func main() {
 	fmt.Println("// generated by go run gen.go; DO NOT EDIT")
 	fmt.Println()
-	fmt.Println("package color")
+	fmt.Println("// Package palette provides standard color palettes.")
+	fmt.Println("package palette")
+	fmt.Println()
+	fmt.Println(`import "image/color"`)
 	fmt.Println()
 	printPlan9()
 	printWebSafe()
@@ -46,14 +49,14 @@ func printPlan9() {
 						c[2] = b * num / den
 					}
 					lines[i+(j&0x0f)] =
-						fmt.Sprintf("\tRGBA{0x%02x, 0x%02x, 0x%02x, 0xff},", c[0], c[1], c[2])
+						fmt.Sprintf("\tcolor.RGBA{0x%02x, 0x%02x, 0x%02x, 0xff},", c[0], c[1], c[2])
 				}
 			}
 		}
 	}
-	fmt.Println("// Plan9Palette is a 256-color palette that partitions the 24-bit RGB space")
+	fmt.Println("// Plan9 is a 256-color palette that partitions the 24-bit RGB space")
 	fmt.Println("// into 4×4×4 subdivision, with 4 shades in each subcube. Compared to the")
-	fmt.Println("// WebSafePalette, the idea is to reduce the color resolution by dicing the")
+	fmt.Println("// WebSafe, the idea is to reduce the color resolution by dicing the")
 	fmt.Println("// color cube into fewer cells, and to use the extra space to increase the")
 	fmt.Println("// intensity resolution. This results in 16 gray shades (4 gray subcubes with")
 	fmt.Println("// 4 samples in each), 13 shades of each primary and secondary color (3")
@@ -63,7 +66,7 @@ func printPlan9() {
 	fmt.Println("//")
 	fmt.Println("// This palette was used in the Plan 9 Operating System, described at")
 	fmt.Println("// http://plan9.bell-labs.com/magic/man2html/6/color")
-	fmt.Println("var Plan9Palette = []Color{")
+	fmt.Println("var Plan9 = []color.Color{")
 	for _, line := range lines {
 		fmt.Println(line)
 	}
@@ -77,15 +80,15 @@ func printWebSafe() {
 		for g := 0; g < 6; g++ {
 			for b := 0; b < 6; b++ {
 				lines[36*r+6*g+b] =
-					fmt.Sprintf("\tRGBA{0x%02x, 0x%02x, 0x%02x, 0xff},", 0x33*r, 0x33*g, 0x33*b)
+					fmt.Sprintf("\tcolor.RGBA{0x%02x, 0x%02x, 0x%02x, 0xff},", 0x33*r, 0x33*g, 0x33*b)
 			}
 		}
 	}
-	fmt.Println("// WebSafePalette is a 216-color palette that was popularized by early versions")
+	fmt.Println("// WebSafe is a 216-color palette that was popularized by early versions")
 	fmt.Println("// of Netscape Navigator. It is also known as the Netscape Color Cube.")
 	fmt.Println("//")
 	fmt.Println("// See http://en.wikipedia.org/wiki/Web_colors#Web-safe_colors for details.")
-	fmt.Println("var WebSafePalette = []Color{")
+	fmt.Println("var WebSafe = []color.Color{")
 	for _, line := range lines {
 		fmt.Println(line)
 	}

src/pkg/image/gif/reader_test.go

@@ -11,11 +11,11 @@ import (
 
 // header, palette and trailer are parts of a valid 2x1 GIF image.
 const (
-	header = "GIF89a" +
+	headerStr = "GIF89a" +
 		"\x02\x00\x01\x00" + // width=2, height=1
 		"\x80\x00\x00" // headerFields=(a color map of 2 pixels), backgroundIndex, aspect
-	palette = "\x10\x20\x30\x40\x50\x60" // the color map, also known as a palette
-	trailer = "\x3b"
+	paletteStr = "\x10\x20\x30\x40\x50\x60" // the color map, also known as a palette
+	trailerStr = "\x3b"
 )
 
 func TestDecode(t *testing.T) {
@@ -41,8 +41,8 @@ func TestDecode(t *testing.T) {
 	}
 	for _, tc := range testCases {
 		b := &bytes.Buffer{}
-		b.WriteString(header)
-		b.WriteString(palette)
+		b.WriteString(headerStr)
+		b.WriteString(paletteStr)
 		// Write an image with bounds 2x1 but tc.nPix pixels. If tc.nPix != 2
 		// then this should result in an invalid GIF image. First, write a
 		// magic 0x2c (image descriptor) byte, bounds=(0,0)-(2,1), a flags
@@ -61,7 +61,7 @@ func TestDecode(t *testing.T) {
 			b.WriteString("\x01\x02") // A 1-byte payload with an 0x02 byte.
 		}
 		b.WriteByte(0x00) // An empty block signifies the end of the image data.
-		b.WriteString(trailer)
+		b.WriteString(trailerStr)
 
 		got, err := Decode(b)
 		if err != tc.wantErr {
@@ -143,7 +143,7 @@ func TestNoPalette(t *testing.T) {
 
 	// Manufacture a GIF with no palette, so any pixel at all
 	// will be invalid.
-	b.WriteString(header[:len(header)-3])
+	b.WriteString(headerStr[:len(headerStr)-3])
 	b.WriteString("\x00\x00\x00") // No global palette.
 
 	// Image descriptor: 2x1, no local palette.
@@ -159,7 +159,7 @@ func TestNoPalette(t *testing.T) {
 	b.Write(enc.Bytes())
 	b.WriteByte(0x00) // An empty block signifies the end of the image data.
 
-	b.WriteString(trailer)
+	b.WriteString(trailerStr)
 
 	try(t, b.Bytes(), "gif: invalid pixel value")
 }
@@ -169,8 +169,8 @@ func TestPixelOutsidePaletteRange(t *testing.T) {
 		b := &bytes.Buffer{}
 
 		// Manufacture a GIF with a 2 color palette.
-		b.WriteString(header)
-		b.WriteString(palette)
+		b.WriteString(headerStr)
+		b.WriteString(paletteStr)
 
 		// Image descriptor: 2x1, no local palette.
 		b.WriteString("\x2c\x00\x00\x00\x00\x02\x00\x01\x00\x00\x02")
@@ -185,7 +185,7 @@ func TestPixelOutsidePaletteRange(t *testing.T) {
 		b.Write(enc.Bytes())
 		b.WriteByte(0x00) // An empty block signifies the end of the image data.
 
-		b.WriteString(trailer)
+		b.WriteString(trailerStr)
 
 		// No error expected, unless the pixels are beyond the 2 color palette.
 		want := ""

src/pkg/image/gif/writer.go

@@ -10,6 +10,7 @@ import (
 	"errors"
 	"image"
 	"image/color"
+	"image/color/palette"
 	"image/draw"
 	"io"
 )
@@ -248,7 +249,7 @@ type Options struct {
 	NumColors int
 
 	// Quantizer is used to produce a palette with size NumColors.
-	// color.Plan9Palette is used in place of a nil Quantizer.
+	// palette.Plan9 is used in place of a nil Quantizer.
 	Quantizer draw.Quantizer
 
 	// Drawer is used to convert the source image to the desired palette.
@@ -308,7 +309,7 @@ func Encode(w io.Writer, m image.Image, o *Options) error {
 	pm, ok := m.(*image.Paletted)
 	if !ok || len(pm.Palette) > opts.NumColors {
 		// TODO: Pick a better sub-sample of the Plan 9 palette.
-		pm = image.NewPaletted(b, color.Plan9Palette[:opts.NumColors])
+		pm = image.NewPaletted(b, palette.Plan9[:opts.NumColors])
 		if opts.Quantizer != nil {
 			pm.Palette = opts.Quantizer.Quantize(make(color.Palette, 0, opts.NumColors), m)
 		}