Prerender labels and cache them as images

src/ol/render/canvas/replaygroup.js

@@ -22,12 +22,13 @@ goog.require('ol.transform');
  * @param {number} tolerance Tolerance.
  * @param {ol.Extent} maxExtent Max extent.
  * @param {number} resolution Resolution.
+ * @param {number} pixelRatio Pixel ratio.
  * @param {boolean} overlaps The replay group can have overlapping geometries.
  * @param {number=} opt_renderBuffer Optional rendering buffer.
  * @struct
  */
 ol.render.canvas.ReplayGroup = function(
-    tolerance, maxExtent, resolution, overlaps, opt_renderBuffer) {
+    tolerance, maxExtent, resolution, pixelRatio, overlaps, opt_renderBuffer) {
   ol.render.ReplayGroup.call(this);
 
   /**
@@ -48,6 +49,12 @@ ol.render.canvas.ReplayGroup = function(
    */
   this.overlaps_ = overlaps;
 
+  /**
+   * @private
+   * @type {number}
+   */
+  this.pixelRatio_ = pixelRatio;
+
   /**
    * @private
    * @type {number}
@@ -296,7 +303,7 @@ ol.render.canvas.ReplayGroup.prototype.getReplay = function(zIndex, replayType)
   if (replay === undefined) {
     var Constructor = ol.render.canvas.ReplayGroup.BATCH_CONSTRUCTORS_[replayType];
     replay = new Constructor(this.tolerance_, this.maxExtent_,
-        this.resolution_, this.overlaps_);
+        this.resolution_, this.pixelRatio_, this.overlaps_);
     replays[replayType] = replay;
   }
   return replay;
@@ -402,7 +409,7 @@ ol.render.canvas.ReplayGroup.prototype.replayHitDetection_ = function(
  * @private
  * @type {Object.<ol.render.ReplayType,
  *                function(new: ol.render.canvas.Replay, number, ol.Extent,
- *                number, boolean)>}
+ *                number, number, boolean)>}
  */
 ol.render.canvas.ReplayGroup.BATCH_CONSTRUCTORS_ = {
   'Circle': ol.render.canvas.PolygonReplay,