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