1 files changed, 57 insertions, 0 deletions
diff --git a/modules/util/color.go b/modules/util/color.go
new file mode 100644
index 0000000..9c520dc
--- /dev/null
+++ b/modules/util/color.go
@@ -0,0 +1,57 @@
+// 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"
+}