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silverwind
75 lines
2.4 KiB
Go
75 lines
2.4 KiB
Go
// Copyright 2023 The Gitea Authors. All rights reserved.
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// SPDX-License-Identifier: MIT
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package util
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import (
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"fmt"
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"math"
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"strconv"
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"strings"
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)
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// HexToRBGColor parses color as RGB values in 0..255 range from the hex color string (with or without #)
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func HexToRBGColor(colorString string) (float64, float64, float64) {
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hexString := colorString
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if strings.HasPrefix(colorString, "#") {
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hexString = colorString[1:]
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}
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// only support transfer of rgb, rgba, rrggbb and rrggbbaa
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// if not in these formats, use default values 0, 0, 0
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if len(hexString) != 3 && len(hexString) != 4 && len(hexString) != 6 && len(hexString) != 8 {
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return 0, 0, 0
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}
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if len(hexString) == 3 || len(hexString) == 4 {
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hexString = fmt.Sprintf("%c%c%c%c%c%c", hexString[0], hexString[0], hexString[1], hexString[1], hexString[2], hexString[2])
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}
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if len(hexString) == 8 {
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hexString = hexString[0:6]
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}
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color, err := strconv.ParseUint(hexString, 16, 32)
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color32 := uint32(color)
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if err != nil {
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return 0, 0, 0
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}
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r := float64(uint8(0xFF & (color32 >> 16)))
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g := float64(uint8(0xFF & (color32 >> 8)))
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b := float64(uint8(0xFF & color32))
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return r, g, b
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}
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// linearizeChannel undoes the sRGB transfer function, channel is in 0..255 range
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func linearizeChannel(channel float64) float64 {
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srgb := channel / 255
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if srgb <= 0.04045 {
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return srgb / 12.92
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}
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return math.Pow((srgb+0.055)/1.055, 2.4)
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}
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// getRelativeLuminance returns relative luminance for a SRGB color - https://www.w3.org/TR/WCAG20/#relativeluminancedef
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// Keep this in sync with web_src/js/utils/color.ts
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func getRelativeLuminance(color string) float64 {
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r, g, b := HexToRBGColor(color)
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return 0.2126*linearizeChannel(r) + 0.7152*linearizeChannel(g) + 0.0722*linearizeChannel(b)
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}
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// GetPerceivedBrightness weights the gamma-encoded channels, so it stays in the same space as the
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// raw channels and can scale them proportionally. Not a luminance, don't use it for contrast.
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func GetPerceivedBrightness(color string) float64 {
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r, g, b := HexToRBGColor(color)
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return (0.2126729*r + 0.7151522*g + 0.0721750*b) / 255
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}
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func UseLightText(backgroundColor string) bool {
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return getRelativeLuminance(backgroundColor) < 0.36 // matches APCA better than WCAG's own 0.179
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}
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// ContrastColor returns a black or white foreground color that the highest contrast ratio.
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func ContrastColor(backgroundColor string) string {
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if UseLightText(backgroundColor) {
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return "#fff"
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}
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return "#000"
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}
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