Add decluttering for images and text

src/ol/render/canvas.js

@@ -1,6 +1,9 @@
 goog.provide('ol.render.canvas');
 
 
+goog.require('ol.transform');
+
+
 /**
  * @const
  * @type {string}
@@ -91,3 +94,41 @@ ol.render.canvas.rotateAtOffset = function(context, rotation, offsetX, offsetY)
     context.translate(-offsetX, -offsetY);
   }
 };
+
+
+ol.render.canvas.resetTransform_ = ol.transform.create();
+
+
+/**
+ * @param {CanvasRenderingContext2D} context Context.
+ * @param {ol.Transform|null} transform Transform.
+ * @param {number} opacity Opacity.
+ * @param {HTMLImageElement|HTMLCanvasElement|HTMLVideoElement} image Image.
+ * @param {number} originX Origin X.
+ * @param {number} originY Origin Y.
+ * @param {number} w Width.
+ * @param {number} h Height.
+ * @param {number} x X.
+ * @param {number} y Y.
+ * @param {number} scale Scale.
+ */
+ol.render.canvas.drawImage = function(context,
+    transform, opacity, image, originX, originY, w, h, x, y, scale) {
+  var alpha;
+  if (opacity != 1) {
+    alpha = context.globalAlpha;
+    context.globalAlpha = alpha * opacity;
+  }
+  if (transform) {
+    context.setTransform.apply(context, transform);
+  }
+
+  context.drawImage(image, originX, originY, w, h, x, y, w * scale, h * scale);
+
+  if (alpha) {
+    context.globalAlpha = alpha;
+  }
+  if (transform) {
+    context.setTransform.apply(context, ol.render.canvas.resetTransform_);
+  }
+};