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gitea/modules/util/color.go

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// Copyright 2023 The Gitea Authors. All rights reserved.
// SPDX-License-Identifier: MIT
package util
import (
"fmt"
"math"
"strconv"
"strings"
)
// Check similar implementation in web_src/js/utils/color.js and keep synchronization
// Return R, G, B values defined in reletive luminance
func getLuminanceRGB(channel float64) float64 {
sRGB := channel / 255
if sRGB <= 0.03928 {
return sRGB / 12.92
}
return math.Pow((sRGB+0.055)/1.055, 2.4)
}
// Get color as RGB values in 0..255 range from the hex color string (with or without #)
func HexToRBGColor(colorString string) (float64, float64, float64) {
hexString := colorString
if strings.HasPrefix(colorString, "#") {
hexString = colorString[1:]
}
// only support transfer of rgb, rgba, rrggbb and rrggbbaa
// if not in these formats, use default values 0, 0, 0
if len(hexString) != 3 && len(hexString) != 4 && len(hexString) != 6 && len(hexString) != 8 {
return 0, 0, 0
}
if len(hexString) == 3 || len(hexString) == 4 {
hexString = fmt.Sprintf("%c%c%c%c%c%c", hexString[0], hexString[0], hexString[1], hexString[1], hexString[2], hexString[2])
}
if len(hexString) == 8 {
hexString = hexString[0:6]
}
color, err := strconv.ParseUint(hexString, 16, 64)
if err != nil {
return 0, 0, 0
}
r := float64(uint8(0xFF & (uint32(color) >> 16)))
g := float64(uint8(0xFF & (uint32(color) >> 8)))
b := float64(uint8(0xFF & uint32(color)))
return r, g, b
}
// return luminance given RGB channels
// Reference from: https://www.w3.org/WAI/GL/wiki/Relative_luminance
func GetLuminance(r, g, b float64) float64 {
R := getLuminanceRGB(r)
G := getLuminanceRGB(g)
B := getLuminanceRGB(b)
luminance := 0.2126*R + 0.7152*G + 0.0722*B
return luminance
}
// Reference from: https://firsching.ch/github_labels.html
// In the future WCAG 3 APCA may be a better solution.
// Check if text should use light color based on RGB of background
func UseLightTextOnBackground(r, g, b float64) bool {
return GetLuminance(r, g, b) < 0.453
}