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// Copyright 2023 The Gitea Authors. All rights reserved.
// SPDX-License-Identifier: MIT
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package util
import (
"fmt"
"strconv"
"strings"
)
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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 ) {
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
}
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// GetRelativeLuminance returns relative luminance for a SRGB color - https://en.wikipedia.org/wiki/Relative_luminance
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// Keep this in sync with web_src/js/utils/color.js
func GetRelativeLuminance ( color string ) float64 {
r , g , b := HexToRBGColor ( color )
return ( 0.2126729 * r + 0.7151522 * g + 0.0721750 * b ) / 255
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}
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func UseLightText ( backgroundColor string ) bool {
return GetRelativeLuminance ( backgroundColor ) < 0.453
}
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// ContrastColor returns a black or white foreground color that the highest contrast ratio.
// In the future, the APCA contrast function, or CSS `contrast-color` will be better.
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// https://github.com/color-js/color.js/blob/eb7b53f7a13bb716ec8b28c7a56f052cd599acd9/src/contrast/APCA.js#L42
func ContrastColor ( backgroundColor string ) string {
if UseLightText ( backgroundColor ) {
return "#fff"
}
return "#000"
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}