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

Documentation: image/color/palette

     1  // Copyright 2013 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // +build ignore
     6  
     7  package main
     8  
     9  // This program generates palette.go. Invoke it as
    10  //	go run gen.go -output palette.go
    11  
    12  import (
    13  	"bytes"
    14  	"flag"
    15  	"fmt"
    16  	"go/format"
    17  	"io"
    18  	"io/ioutil"
    19  	"log"
    20  )
    21  
    22  var filename = flag.String("output", "palette.go", "output file name")
    23  
    24  func main() {
    25  	flag.Parse()
    26  
    27  	var buf bytes.Buffer
    28  
    29  	fmt.Fprintln(&buf, `// Copyright 2013 The Go Authors. All rights reserved.
    30  // Use of this source code is governed by a BSD-style
    31  // license that can be found in the LICENSE file.`)
    32  	fmt.Fprintln(&buf)
    33  	fmt.Fprintln(&buf, "// generated by go run gen.go -output palette.go; DO NOT EDIT")
    34  	fmt.Fprintln(&buf)
    35  	fmt.Fprintln(&buf, "package palette")
    36  	fmt.Fprintln(&buf)
    37  	fmt.Fprintln(&buf, `import "image/color"`)
    38  	fmt.Fprintln(&buf)
    39  	printPlan9(&buf)
    40  	printWebSafe(&buf)
    41  
    42  	data, err := format.Source(buf.Bytes())
    43  	if err != nil {
    44  		log.Fatal(err)
    45  	}
    46  	err = ioutil.WriteFile(*filename, data, 0644)
    47  	if err != nil {
    48  		log.Fatal(err)
    49  	}
    50  }
    51  
    52  func printPlan9(w io.Writer) {
    53  	c, lines := [3]int{}, [256]string{}
    54  	for r, i := 0, 0; r != 4; r++ {
    55  		for v := 0; v != 4; v, i = v+1, i+16 {
    56  			for g, j := 0, v-r; g != 4; g++ {
    57  				for b := 0; b != 4; b, j = b+1, j+1 {
    58  					den := r
    59  					if g > den {
    60  						den = g
    61  					}
    62  					if b > den {
    63  						den = b
    64  					}
    65  					if den == 0 {
    66  						c[0] = 0x11 * v
    67  						c[1] = 0x11 * v
    68  						c[2] = 0x11 * v
    69  					} else {
    70  						num := 17 * (4*den + v)
    71  						c[0] = r * num / den
    72  						c[1] = g * num / den
    73  						c[2] = b * num / den
    74  					}
    75  					lines[i+(j&0x0f)] =
    76  						fmt.Sprintf("\tcolor.RGBA{0x%02x, 0x%02x, 0x%02x, 0xff},", c[0], c[1], c[2])
    77  				}
    78  			}
    79  		}
    80  	}
    81  	fmt.Fprintln(w, "// Plan9 is a 256-color palette that partitions the 24-bit RGB space")
    82  	fmt.Fprintln(w, "// into 4×4×4 subdivision, with 4 shades in each subcube. Compared to the")
    83  	fmt.Fprintln(w, "// WebSafe, the idea is to reduce the color resolution by dicing the")
    84  	fmt.Fprintln(w, "// color cube into fewer cells, and to use the extra space to increase the")
    85  	fmt.Fprintln(w, "// intensity resolution. This results in 16 gray shades (4 gray subcubes with")
    86  	fmt.Fprintln(w, "// 4 samples in each), 13 shades of each primary and secondary color (3")
    87  	fmt.Fprintln(w, "// subcubes with 4 samples plus black) and a reasonable selection of colors")
    88  	fmt.Fprintln(w, "// covering the rest of the color cube. The advantage is better representation")
    89  	fmt.Fprintln(w, "// of continuous tones.")
    90  	fmt.Fprintln(w, "//")
    91  	fmt.Fprintln(w, "// This palette was used in the Plan 9 Operating System, described at")
    92  	fmt.Fprintln(w, "// https://9p.io/magic/man2html/6/color")
    93  	fmt.Fprintln(w, "var Plan9 = []color.Color{")
    94  	for _, line := range lines {
    95  		fmt.Fprintln(w, line)
    96  	}
    97  	fmt.Fprintln(w, "}")
    98  	fmt.Fprintln(w)
    99  }
   100  
   101  func printWebSafe(w io.Writer) {
   102  	lines := [6 * 6 * 6]string{}
   103  	for r := 0; r < 6; r++ {
   104  		for g := 0; g < 6; g++ {
   105  			for b := 0; b < 6; b++ {
   106  				lines[36*r+6*g+b] =
   107  					fmt.Sprintf("\tcolor.RGBA{0x%02x, 0x%02x, 0x%02x, 0xff},", 0x33*r, 0x33*g, 0x33*b)
   108  			}
   109  		}
   110  	}
   111  	fmt.Fprintln(w, "// WebSafe is a 216-color palette that was popularized by early versions")
   112  	fmt.Fprintln(w, "// of Netscape Navigator. It is also known as the Netscape Color Cube.")
   113  	fmt.Fprintln(w, "//")
   114  	fmt.Fprintln(w, "// See http://en.wikipedia.org/wiki/Web_colors#Web-safe_colors for details.")
   115  	fmt.Fprintln(w, "var WebSafe = []color.Color{")
   116  	for _, line := range lines {
   117  		fmt.Fprintln(w, line)
   118  	}
   119  	fmt.Fprintln(w, "}")
   120  	fmt.Fprintln(w)
   121  }
   122  

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