Pull in euzuro's patch from #366 - changing how maxResolution is set and a number of other efficiency changes

git-svn-id: http://svn.openlayers.org/trunk/openlayers@1737 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Layer/Image.js

@@ -1,6 +1,7 @@
 /* Copyright (c) 2006 MetaCarta, Inc., published under a modified BSD license.
  * See http://svn.openlayers.org/trunk/openlayers/repository-license.txt 
  * for the full text of the license. */
+ 
 /**
  * @fileoverview Image Layer
  * @author Tim Schaub
@@ -15,8 +16,10 @@ OpenLayers.Layer.Image = OpenLayers.Class.create();
 OpenLayers.Layer.Image.prototype = 
   OpenLayers.Class.inherit(OpenLayers.Layer, {
 
-    /** @type String */
+    /** By default, Layer.Image will be a baselayer
-    name: null,
+     * 
+     * @type Boolean */
+    isBaseLayer: true,
     
     /** @type String */
     url: null,
@@ -27,14 +30,10 @@ OpenLayers.Layer.Image.prototype =
     /** @type OpenLayers.Size */
     size: null,
 
-    /** @type Object */
-    options: null,
-
     /** @type OpenLayers.Tile.Image */
     tile: null,
 
-    /**
+    /** The ratio of height/width represented by a single pixel in the graphic
-     * The ratio of height/width represented by a single pixel in the graphic
      * 
      * @type Float */
     aspectRatio: null,
@@ -52,14 +51,10 @@ OpenLayers.Layer.Image.prototype =
         this.url = url;
         this.extent = extent;
         this.size = size;
-        this.aspectRatio = (this.extent.getHeight() / this.size.h) /
-                           (this.extent.getWidth() / this.size.w);
         OpenLayers.Layer.prototype.initialize.apply(this, [name, options]);
 
-        // unless explicitly set in options, the layer will be a base layer
+        this.aspectRatio = (this.extent.getHeight() / this.size.h) /
-        if((options == null) || (options.isBaseLayer == null)) {
+                           (this.extent.getWidth() / this.size.w);
-            this.isBaseLayer = true;
-        }
     },    
 
     /**
@@ -95,41 +90,19 @@ OpenLayers.Layer.Image.prototype =
         return obj;
     },    
     
-    /**
-     * This is a bad method to have here.  It would be nicer to be able
-     * to ask Layer directly.
-     */
-    shouldCalcResolutions: function() {
-        var props = new Array(
-            'scales', 'resolutions',
-            'maxScale', 'minScale', 
-            'maxResolution', 'minResolution', 
-            'minExtent', 'maxExtent',
-            'numZoomLevels', 'maxZoomLevel'
-        );
-        for(var i=0; i < props.length; i++) {
-            var property = props[i];
-            if(this.options[property] != null) {
-                return false;
-            }
-        }
-        return true;
-    },
-        
-    
     /**
      * @param {OpenLayers.Map} map
      */
     setMap: function(map) {
         // If nothing to do with resolutions has been set, assume a single
         //  resolution determined by extent/size
-        if(this.shouldCalcResolutions()) {
+        if( this.options.maxResolution == null ) {
-            this.options.resolutions = [this.extent.getWidth() / this.size.w];
+        	this.options.maxResolution = this.extent.getWidth() / this.size.w;
         }
         OpenLayers.Layer.prototype.setMap.apply(this, arguments);
     },
 
-    /** When zooming or first rendering, create a new tile for the image.
+    /** Create the tile for the image or resize it for the new resolution
      * 
      * @param {OpenLayers.Bounds} bounds
      * @param {Boolean} zoomChanged
@@ -142,15 +115,6 @@ OpenLayers.Layer.Image.prototype =
 
         if(zoomChanged || firstRendering) {
 
-            //clear out the old tile
-            if(this.tile) {
-                this.tile.destroy();
-                this.tile = null;
-            }
-            
-            //determine new tile bounds
-            var tileBounds = this.extent.clone();
-
             //determine new tile size
             var tileWidth = this.extent.getWidth() / this.map.getResolution();
             var tileHeight = this.extent.getHeight() /
@@ -158,11 +122,18 @@ OpenLayers.Layer.Image.prototype =
             var tileSize = new OpenLayers.Size(tileWidth, tileHeight);
             
             //determine new position (upper left corner of new bounds)
-            var ul = new OpenLayers.LonLat(tileBounds.left, tileBounds.top);
+            var ul = new OpenLayers.LonLat(this.extent.left, this.extent.top);
-            var pos = this.map.getLayerPxFromLonLat(ul);
+            var ulPx = this.map.getLayerPxFromLonLat(ul);
 
-            this.tile = new OpenLayers.Tile.Image(this, pos, tileBounds, 
+            if(firstRendering) {
+                //create the new tile
+                this.tile = new OpenLayers.Tile.Image(this, ulPx, this.extent, 
                                                       this.url, tileSize);
+            } else {
+                //just resize the tile and set it's new position
+                this.tile.size = tileSize.clone();
+                this.tile.position = ulPx.clone();
+            }
             this.tile.draw();
         }
     }, 
@@ -172,10 +143,13 @@ OpenLayers.Layer.Image.prototype =
      */
     setUrl: function(newUrl) {
         this.url = newUrl;
-        this.moveTo();
+        this.draw();
     },
 
-    /**
+    /** The url we return is always the same (the image itself never changes)
+     *   so we can ignore the bounds parameter (it will always be the same, 
+     *   anyways) 
+     * 
      * @param {OpenLayers.Bounds} bounds
      */
     getURL: function(bounds) {