github.com/comwrg/go/src@v0.0.0-20220319063731-c238d0440370/image/color/palette/gen.go (about)

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