add color util

src/util/ColorUtil.ts

@@ -0,0 +1,51 @@
+//from this gist https://gist.github.com/jfsiii/5641126
+
+// from http://www.w3.org/TR/WCAG20/#relativeluminancedef
+export function relativeLuminanceW3C(
+  R8bit: number,
+  G8bit: number,
+  B8bit: number
+) {
+  const RsRGB = R8bit / 255;
+  const GsRGB = G8bit / 255;
+  const BsRGB = B8bit / 255;
+
+  const R =
+    RsRGB <= 0.03928 ? RsRGB / 12.92 : Math.pow((RsRGB + 0.055) / 1.055, 2.4);
+  const G =
+    GsRGB <= 0.03928 ? GsRGB / 12.92 : Math.pow((GsRGB + 0.055) / 1.055, 2.4);
+  const B =
+    BsRGB <= 0.03928 ? BsRGB / 12.92 : Math.pow((BsRGB + 0.055) / 1.055, 2.4);
+
+  // For the sRGB colorspace, the relative luminance of a color is defined as:
+  const L = 0.2126 * R + 0.7152 * G + 0.0722 * B;
+
+  return L;
+}
+
+export function relativeLuminanceW3CHexColor(hexColor: string): number {
+  const [r, g, b] = hexToRgb(hexColor);
+  return relativeLuminanceW3C(r, g, b);
+}
+
+// from https://www.codegrepper.com/code-examples/javascript/javascript+convert+color+string+to+rgb
+export function rgbToHex(r: number, g: number, b: number): string {
+  return "#" + ((1 << 24) + (r << 16) + (g << 8) + b).toString(16).slice(1);
+}
+
+// from https://www.codegrepper.com/code-examples/javascript/javascript+convert+color+string+to+rgb
+export function hexToRgb(
+  hex: string,
+  result = /^#?([a-f\d]{2})([a-f\d]{2})([a-f\d]{2})$/i.exec(hex)
+): number[] {
+  return result ? result.map((i) => parseInt(i, 16)).slice(1) : null;
+  //returns [23, 14, 45] -> reformat if needed
+}
+
+export function getColorByLuminance(
+  color: string,
+  lightColor: string,
+  darkColor: string
+): string {
+  return relativeLuminanceW3CHexColor(color) < 0.5 ? darkColor : lightColor;
+}