Changed rainbow algorithm

Author: ginnyTheCat

src/utils/colour.js

@@ -0,0 +1,87 @@
+/*
+Copyright 2019 Michael Telatynski <[email protected]>
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import { number } from "prop-types";
+
+export function textToHtmlRainbow(str: string): string {
+    const frequency = (2 * Math.PI) / str.length;
+
+    return Array.from(str)
+        .map((c, i) => {
+            if (c === " ") {
+                return c;
+            }
+            const [a, b] = generateAB(i * frequency, 1);
+            const [red, green, blue] = labToRGB(75, a, b);
+            return (
+                '<font color="#' +
+                red.toString(16).padStart(2, "0") +
+                green.toString(16).padStart(2, "0") +
+                blue.toString(16).padStart(2, "0") +
+                '">' +
+                c +
+                "</font>"
+            );
+        })
+        .join("");
+}
+
+function generateAB(hue: number, chroma: number): [number, number] {
+    const a = chroma * 127 * Math.cos(hue);
+    const b = chroma * 127 * Math.sin(hue);
+
+    return [a, b];
+}
+
+function labToRGB(l: number, a: number, b: number): [number, number, number] {
+    // Convert CIELAB to CIEXYZ (D65)
+    var y = (l + 16) / 116;
+    const x = adjustXYZ(y + a / 500) * 0.9505;
+    const z = adjustXYZ(y - b / 200) * 1.089;
+
+    y = adjustXYZ(y);
+
+    // Linear transformation from CIEXYZ to RGB
+    const red = 3.24096994 * x - 1.53738318 * y - 0.49861076 * z;
+    const green = -0.96924364 * x + 1.8759675 * y + 0.04155506 * z;
+    const blue = 0.05563008 * x - 0.20397696 * y + 1.05697151 * z;
+
+    return [adjustRGB(red), adjustRGB(green), adjustRGB(blue)];
+}
+
+function adjustXYZ(v: number): number {
+    if (v > 0.2069) {
+        return Math.pow(v, 3);
+    }
+    return 0.1284 * v - 0.01771;
+}
+
+function gammaCorrection(v: number): number {
+    // Non-linear transformation to sRGB
+    if (v <= 0.0031308) {
+        return 12.92 * v;
+    }
+    return 1.055 * Math.pow(v, 1 / 2.4) - 0.055;
+}
+
+function adjustRGB(v: number): number {
+    const corrected = gammaCorrection(v);
+
+    // Limits number between 0 and 1
+    const limited = Math.min(Math.max(corrected, 0), 1);
+
+    return Math.round(limited * 255);
+}