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 444 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
