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Source file src/image/color/palette/gen.go

Documentation: image/color/palette

  // Copyright 2013 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.
  
  // +build ignore
  
  package main
  
  // This program generates palette.go. Invoke it as
  //	go run gen.go -output palette.go
  
  import (
  	"bytes"
  	"flag"
  	"fmt"
  	"go/format"
  	"io"
  	"io/ioutil"
  	"log"
  )
  
  var filename = flag.String("output", "palette.go", "output file name")
  
  func main() {
  	flag.Parse()
  
  	var buf bytes.Buffer
  
  	fmt.Fprintln(&buf, `// Copyright 2013 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.`)
  	fmt.Fprintln(&buf)
  	fmt.Fprintln(&buf, "// generated by go run gen.go -output palette.go; DO NOT EDIT")
  	fmt.Fprintln(&buf)
  	fmt.Fprintln(&buf, "package palette")
  	fmt.Fprintln(&buf)
  	fmt.Fprintln(&buf, `import "image/color"`)
  	fmt.Fprintln(&buf)
  	printPlan9(&buf)
  	printWebSafe(&buf)
  
  	data, err := format.Source(buf.Bytes())
  	if err != nil {
  		log.Fatal(err)
  	}
  	err = ioutil.WriteFile(*filename, data, 0644)
  	if err != nil {
  		log.Fatal(err)
  	}
  }
  
  func printPlan9(w io.Writer) {
  	c, lines := [3]int{}, [256]string{}
  	for r, i := 0, 0; r != 4; r++ {
  		for v := 0; v != 4; v, i = v+1, i+16 {
  			for g, j := 0, v-r; g != 4; g++ {
  				for b := 0; b != 4; b, j = b+1, j+1 {
  					den := r
  					if g > den {
  						den = g
  					}
  					if b > den {
  						den = b
  					}
  					if den == 0 {
  						c[0] = 0x11 * v
  						c[1] = 0x11 * v
  						c[2] = 0x11 * v
  					} else {
  						num := 17 * (4*den + v)
  						c[0] = r * num / den
  						c[1] = g * num / den
  						c[2] = b * num / den
  					}
  					lines[i+(j&0x0f)] =
  						fmt.Sprintf("\tcolor.RGBA{0x%02x, 0x%02x, 0x%02x, 0xff},", c[0], c[1], c[2])
  				}
  			}
  		}
  	}
  	fmt.Fprintln(w, "// Plan9 is a 256-color palette that partitions the 24-bit RGB space")
  	fmt.Fprintln(w, "// into 4×4×4 subdivision, with 4 shades in each subcube. Compared to the")
  	fmt.Fprintln(w, "// WebSafe, the idea is to reduce the color resolution by dicing the")
  	fmt.Fprintln(w, "// color cube into fewer cells, and to use the extra space to increase the")
  	fmt.Fprintln(w, "// intensity resolution. This results in 16 gray shades (4 gray subcubes with")
  	fmt.Fprintln(w, "// 4 samples in each), 13 shades of each primary and secondary color (3")
  	fmt.Fprintln(w, "// subcubes with 4 samples plus black) and a reasonable selection of colors")
  	fmt.Fprintln(w, "// covering the rest of the color cube. The advantage is better representation")
  	fmt.Fprintln(w, "// of continuous tones.")
  	fmt.Fprintln(w, "//")
  	fmt.Fprintln(w, "// This palette was used in the Plan 9 Operating System, described at")
  	fmt.Fprintln(w, "// https://9p.io/magic/man2html/6/color")
  	fmt.Fprintln(w, "var Plan9 = []color.Color{")
  	for _, line := range lines {
  		fmt.Fprintln(w, line)
  	}
  	fmt.Fprintln(w, "}")
  	fmt.Fprintln(w)
  }
  
  func printWebSafe(w io.Writer) {
  	lines := [6 * 6 * 6]string{}
  	for r := 0; r < 6; r++ {
  		for g := 0; g < 6; g++ {
  			for b := 0; b < 6; b++ {
  				lines[36*r+6*g+b] =
  					fmt.Sprintf("\tcolor.RGBA{0x%02x, 0x%02x, 0x%02x, 0xff},", 0x33*r, 0x33*g, 0x33*b)
  			}
  		}
  	}
  	fmt.Fprintln(w, "// WebSafe is a 216-color palette that was popularized by early versions")
  	fmt.Fprintln(w, "// of Netscape Navigator. It is also known as the Netscape Color Cube.")
  	fmt.Fprintln(w, "//")
  	fmt.Fprintln(w, "// See http://en.wikipedia.org/wiki/Web_colors#Web-safe_colors for details.")
  	fmt.Fprintln(w, "var WebSafe = []color.Color{")
  	for _, line := range lines {
  		fmt.Fprintln(w, line)
  	}
  	fmt.Fprintln(w, "}")
  	fmt.Fprintln(w)
  }
  

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