Move webgl utils out of ol/renderer/webgl/Layer module into their own module

src/ol/render/webgl/utils.js

@@ -0,0 +1,142 @@
+/**
+ * @module ol/render/webgl/utils
+ */
+const tmpArray_ = [];
+const bufferPositions_ = {vertexPosition: 0, indexPosition: 0};
+
+function writePointVertex(buffer, pos, x, y, index) {
+  buffer[pos + 0] = x;
+  buffer[pos + 1] = y;
+  buffer[pos + 2] = index;
+}
+
+/**
+ * An object holding positions both in an index and a vertex buffer.
+ * @typedef {Object} BufferPositions
+ * @property {number} vertexPosition Position in the vertex buffer
+ * @property {number} indexPosition Position in the index buffer
+ */
+
+/**
+ * Pushes a quad (two triangles) based on a point geometry
+ * @param {Float32Array} instructions Array of render instructions for points.
+ * @param {number} elementIndex Index from which render instructions will be read.
+ * @param {Float32Array} vertexBuffer Buffer in the form of a typed array.
+ * @param {Uint32Array} indexBuffer Buffer in the form of a typed array.
+ * @param {number} customAttributesCount Amount of custom attributes for each element.
+ * @param {BufferPositions} [bufferPositions] Buffer write positions; if not specified, positions will be set at 0.
+ * @return {BufferPositions} New buffer positions where to write next
+ * @property {number} vertexPosition New position in the vertex buffer where future writes should start.
+ * @property {number} indexPosition New position in the index buffer where future writes should start.
+ * @private
+ */
+export function writePointFeatureToBuffers(
+  instructions,
+  elementIndex,
+  vertexBuffer,
+  indexBuffer,
+  customAttributesCount,
+  bufferPositions
+) {
+  // This is for x, y and index
+  const baseVertexAttrsCount = 3;
+  const baseInstructionsCount = 2;
+  const stride = baseVertexAttrsCount + customAttributesCount;
+
+  const x = instructions[elementIndex + 0];
+  const y = instructions[elementIndex + 1];
+
+  // read custom numerical attributes on the feature
+  const customAttrs = tmpArray_;
+  customAttrs.length = customAttributesCount;
+  for (let i = 0; i < customAttrs.length; i++) {
+    customAttrs[i] = instructions[elementIndex + baseInstructionsCount + i];
+  }
+
+  let vPos = bufferPositions ? bufferPositions.vertexPosition : 0;
+  let iPos = bufferPositions ? bufferPositions.indexPosition : 0;
+  const baseIndex = vPos / stride;
+
+  // push vertices for each of the four quad corners (first standard then custom attributes)
+  writePointVertex(vertexBuffer, vPos, x, y, 0);
+  customAttrs.length &&
+    vertexBuffer.set(customAttrs, vPos + baseVertexAttrsCount);
+  vPos += stride;
+
+  writePointVertex(vertexBuffer, vPos, x, y, 1);
+  customAttrs.length &&
+    vertexBuffer.set(customAttrs, vPos + baseVertexAttrsCount);
+  vPos += stride;
+
+  writePointVertex(vertexBuffer, vPos, x, y, 2);
+  customAttrs.length &&
+    vertexBuffer.set(customAttrs, vPos + baseVertexAttrsCount);
+  vPos += stride;
+
+  writePointVertex(vertexBuffer, vPos, x, y, 3);
+  customAttrs.length &&
+    vertexBuffer.set(customAttrs, vPos + baseVertexAttrsCount);
+  vPos += stride;
+
+  indexBuffer[iPos++] = baseIndex;
+  indexBuffer[iPos++] = baseIndex + 1;
+  indexBuffer[iPos++] = baseIndex + 3;
+  indexBuffer[iPos++] = baseIndex + 1;
+  indexBuffer[iPos++] = baseIndex + 2;
+  indexBuffer[iPos++] = baseIndex + 3;
+
+  bufferPositions_.vertexPosition = vPos;
+  bufferPositions_.indexPosition = iPos;
+
+  return bufferPositions_;
+}
+
+/**
+ * Returns a texture of 1x1 pixel, white
+ * @private
+ * @return {ImageData} Image data.
+ */
+export function getBlankImageData() {
+  const canvas = document.createElement('canvas');
+  const image = canvas.getContext('2d').createImageData(1, 1);
+  image.data[0] = 255;
+  image.data[1] = 255;
+  image.data[2] = 255;
+  image.data[3] = 255;
+  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;
+}