Webgl points / read only one pixel for feature hit detection

Also implements `hasFeatureAtCoordinate`.

`hitTolerance` is not supported for now.

src/ol/renderer/webgl/Layer.js

@@ -3,6 +3,7 @@
  */
 import LayerRenderer from '../Layer.js';
 import WebGLHelper from '../../webgl/Helper.js';
+import {TRUE} from '../../functions.js';
 
 
 /**
@@ -81,6 +82,14 @@ class WebGLLayerRenderer extends LayerRenderer {
   getShaderCompileErrors() {
     return this.helper.getShaderCompileErrors();
   }
+
+  /**
+   * @inheritDoc
+   */
+  hasFeatureAtCoordinate(coordinate, frameState) {
+    const feature = this.forEachFeatureAtCoordinate(coordinate, frameState, 0, TRUE, null);
+    return feature !== undefined;
+  }
 }
 
 

src/ol/renderer/webgl/PointsLayer.js

@@ -377,6 +377,7 @@ class WebGLPointsLayerRenderer extends WebGLLayerRenderer {
     }
 
     this.renderHitDetection(frameState);
+    this.hitRenderTarget_.clearCachedData();
 
     return canvas;
   }
@@ -533,17 +534,14 @@ class WebGLPointsLayerRenderer extends WebGLLayerRenderer {
    * @inheritDoc
    */
   forEachFeatureAtCoordinate(coordinate, frameState, hitTolerance, callback, declutteredFeatures) {
-    const pixel = applyTransform(frameState.coordinateToPixelTransform, coordinate.slice(0, 2));
-    const width = frameState.size[0];
-    const height = frameState.size[1];
+    const pixel = applyTransform(frameState.coordinateToPixelTransform, coordinate.slice());
 
-    const data = this.hitRenderTarget_.read();
-    const index = Math.floor(pixel[0]) + (height - Math.floor(pixel[1])) * width;
+    const data = this.hitRenderTarget_.readPixel(pixel[0], pixel[1]);
     const color = [
-      data[index * 4] / 255,
-      data[index * 4 + 1] / 255,
-      data[index * 4 + 2] / 255,
-      data[index * 4 + 3] / 255
+      data[0] / 255,
+      data[1] / 255,
+      data[2] / 255,
+      data[3] / 255
     ];
     const uid = colorDecodeId(color).toString();
 

src/ol/webgl/RenderTarget.js

@@ -118,6 +118,7 @@ class WebGLRenderTarget {
    * @param {number} x Pixel coordinate
    * @param {number} y Pixel coordinate
    * @returns {Uint8Array} Integer array with one color value (4 components)
+   * @api
    */
   readPixel(x, y) {
     this.readAll();