Webgl renderer / add id encode/decode utils

src/ol/renderer/webgl/Layer.js

@@ -238,4 +238,40 @@ export function getBlankTexture() {
   return image;
 }
 
+/**
+ * Generates a color array based on a numerical id
+ * Note: the range for each component is 0 to 1 with 256 steps
+ * @param {number} id Id
+ * @param {Array<number>} [opt_array] Reusable array
+ * @return {Array<number>} Color array containing the encoded id
+ */
+export function colorEncodeId(id, opt_array) {
+  const array = opt_array || [];
+  const radix = 256;
+  const divide = radix - 1;
+  array[0] = Math.floor(id / radix / radix / radix) / divide;
+  array[1] = (Math.floor(id / radix / radix) % radix) / divide;
+  array[2] = (Math.floor(id / radix) % radix) / divide;
+  array[3] = (id % radix) / divide;
+  return array;
+}
+
+
+/**
+ * Reads an id from a color-encoded array
+ * Note: the expected range for each component is 0 to 1 with 256 steps.
+ * @param {Array<number>} color Color array containing the encoded id
+ * @return {number} Decoded id
+ */
+export function colorDecodeId(color) {
+  let id = 0;
+  const radix = 256;
+  const mult = radix - 1;
+  id += Math.round(color[0] * radix * radix * radix * mult);
+  id += Math.round(color[1] * radix * radix * mult);
+  id += Math.round(color[2] * radix * mult);
+  id += Math.round(color[3] * mult);
+  return id;
+}
+
 export default WebGLLayerRenderer;