Introduce an icon image cache

src/ol/style/iconstyle.js

@@ -2,6 +2,7 @@
 
 goog.provide('ol.style.Icon');
 goog.provide('ol.style.IconAnchorUnits');
+goog.provide('ol.style.IconImageCache');
 
 goog.require('goog.array');
 goog.require('goog.asserts');
@@ -395,3 +396,83 @@ ol.style.IconImage_.prototype.unlistenImage_ = function() {
   goog.array.forEach(this.imageListenerKeys_, goog.events.unlistenByKey);
   this.imageListenerKeys_ = null;
 };
+
+
+
+/**
+ * @constructor
+ */
+ol.style.IconImageCache = function() {
+
+  /**
+   * @type {Object.<string, ol.style.IconImage_>}
+   * @private
+   */
+  this.cache_ = {};
+
+  /**
+   * @type {number}
+   * @private
+   */
+  this.cacheSize_ = 0;
+
+  /**
+   * @const
+   * @type {number}
+   * @private
+   */
+  this.maxCacheSize_ = 32;
+};
+goog.addSingletonGetter(ol.style.IconImageCache);
+
+
+/**
+ * @param {string} src Src.
+ * @param {?string} crossOrigin Cross origin.
+ * @return {string} Cache key.
+ */
+ol.style.IconImageCache.getKey = function(src, crossOrigin) {
+  goog.asserts.assert(goog.isDef(crossOrigin));
+  return crossOrigin + ':' + src;
+};
+
+
+/**
+ * FIXME empty description for jsdoc
+ */
+ol.style.IconImageCache.prototype.expire = function() {
+  if (this.cacheSize_ > this.maxCacheSize_) {
+    var i = 0;
+    var key, iconImage;
+    for (key in this.cache_) {
+      iconImage = this.cache_[key];
+      if ((i++ & 3) === 0 && !goog.events.hasListener(iconImage)) {
+        delete this.cache_[key];
+        --this.cacheSize_;
+      }
+    }
+  }
+};
+
+
+/**
+ * @param {string} src Src.
+ * @param {?string} crossOrigin Cross origin.
+ * @return {ol.style.IconImage_} Icon image.
+ */
+ol.style.IconImageCache.prototype.get = function(src, crossOrigin) {
+  var key = ol.style.IconImageCache.getKey(src, crossOrigin);
+  return key in this.cache_ ? this.cache_[key] : null;
+};
+
+
+/**
+ * @param {string} src Src.
+ * @param {?string} crossOrigin Cross origin.
+ * @param {ol.style.IconImage_} iconImage Icon image.
+ */
+ol.style.IconImageCache.prototype.set = function(src, crossOrigin, iconImage) {
+  var key = ol.style.IconImageCache.getKey(src, crossOrigin);
+  this.cache_[key] = iconImage;
+  ++this.cacheSize_;
+};