Reproject image sources only if actually needed

src/ol/source/imagesource.js

@@ -5,9 +5,9 @@ goog.require('goog.array');
 goog.require('goog.asserts');
 goog.require('goog.events.Event');
 goog.require('ol.Attribution');
-goog.require('ol.Extent');
 goog.require('ol.ImageState');
 goog.require('ol.array');
+goog.require('ol.extent');
 goog.require('ol.proj');
 goog.require('ol.reproj.Image');
 goog.require('ol.source.Source');
@@ -58,6 +58,20 @@ ol.source.Image = function(options) {
             return b - a;
           }, true), 'resolutions must be null or sorted in descending order');
 
+
+  /**
+   * @private
+   * @type {ol.reproj.Image}
+   */
+  this.reprojectedImage_ = null;
+
+
+  /**
+   * @private
+   * @type {number}
+   */
+  this.reprojectedRevision_ = 0;
+
 };
 goog.inherits(ol.source.Image, ol.source.Source);
 
@@ -104,14 +118,28 @@ ol.source.Image.prototype.getImage =
     }
     return this.getImageInternal(extent, resolution, pixelRatio, projection);
   } else {
-    var image = new ol.reproj.Image(
+    if (!goog.isNull(this.reprojectedImage_)) {
+      if (this.reprojectedRevision_ == this.getRevision() &&
+          ol.proj.equivalent(
+              this.reprojectedImage_.getProjection(), projection) &&
+          this.reprojectedImage_.getResolution() == resolution &&
+          this.reprojectedImage_.getPixelRatio() == pixelRatio &&
+          ol.extent.equals(this.reprojectedImage_.getExtent(), extent)) {
+        return this.reprojectedImage_;
+      }
+      this.reprojectedImage_.dispose();
+      this.reprojectedImage_ = null;
+    }
+
+    this.reprojectedImage_ = new ol.reproj.Image(
         sourceProjection, projection, extent, resolution, pixelRatio,
         goog.bind(function(extent, resolution, pixelRatio) {
           return this.getImageInternal(extent, resolution,
               pixelRatio, sourceProjection);
         }, this));
+    this.reprojectedRevision_ = this.getRevision();
 
-    return image;
+    return this.reprojectedImage_;
   }
 };