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forgejo/modules/util/color.go
silverwind f6c0c39f1a
[PORT] gitea##30237: Fix and rewrite contrast color calculation, fix project-related bugs
1. The previous color contrast calculation function was incorrect at
least for the `#84b6eb` where it output low-contrast white instead of
black. I've rewritten these functions now to accept hex colors and to
match GitHub's calculation and to output pure white/black for maximum
contrast. Before and after:
<img width="94" alt="Screenshot 2024-04-02 at 01 53 46"
src="https://github.com/go-gitea/gitea/assets/115237/00b39e15-a377-4458-95cf-ceec74b78228"><img
width="90" alt="Screenshot 2024-04-02 at 01 51 30"
src="https://github.com/go-gitea/gitea/assets/115237/1677067a-8d8f-47eb-82c0-76330deeb775">

2. Fix project-related issues:

- Expose the new `ContrastColor` function as template helper and use it
for project cards, replacing the previous JS solution which eliminates a
flash of wrong color on page load.
- Fix a bug where if editing a project title, the counter would get
lost.
- Move `rgbToHex` function to color utils.

Co-authored-by: delvh <dev.lh@web.de>
Co-authored-by: Giteabot <teabot@gitea.io>

---
Conflict resolution: Trivial.
(cherry picked from commit 36887ed3921d03f1864360c95bd2ecf853bfbe72)
2024-04-15 16:11:34 +02:00

57 lines
1.9 KiB
Go

// Copyright 2023 The Gitea Authors. All rights reserved.
// SPDX-License-Identifier: MIT
package util
import (
"fmt"
"strconv"
"strings"
)
// 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
}
// Returns relative luminance for a SRGB color - https://en.wikipedia.org/wiki/Relative_luminance
// 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
}
func UseLightText(backgroundColor string) bool {
return GetRelativeLuminance(backgroundColor) < 0.453
}
// Given a background color, 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.
// 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"
}