apply patch from #1106, minor tweaks for performance. (Closes #1106)

git-svn-id: http://svn.openlayers.org/trunk/openlayers@5243 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Layer/Grid.js

@@ -341,6 +341,10 @@ OpenLayers.Layer.Grid = OpenLayers.Class(OpenLayers.Layer.HTTPRequest, {
 
         var rowidx = 0;
         
+        var layerContainerDivLeft = parseInt(this.map.layerContainerDiv.style.left);
+        var layerContainerDivTop = parseInt(this.map.layerContainerDiv.style.top);
+        
+    
         do {
             var row = this.grid[rowidx++];
             if (!row) {
@@ -360,10 +364,10 @@ OpenLayers.Layer.Grid = OpenLayers.Class(OpenLayers.Layer.HTTPRequest, {
                                           tileoffsetlat + tilelat);
 
                 var x = tileoffsetx;
-                x -= parseInt(this.map.layerContainerDiv.style.left);
+                x -= layerContainerDivLeft;
 
                 var y = tileoffsety;
-                y -= parseInt(this.map.layerContainerDiv.style.top);
+                y -= layerContainerDivTop;
 
                 var px = new OpenLayers.Pixel(x, y);
                 var tile = row[colidx++];
@@ -560,13 +564,14 @@ OpenLayers.Layer.Grid = OpenLayers.Class(OpenLayers.Layer.HTTPRequest, {
      */
     shiftRow:function(prepend) {
         var modelRowIndex = (prepend) ? 0 : (this.grid.length - 1);
-        var modelRow = this.grid[modelRowIndex];
+        var grid = this.grid;
+        var modelRow = grid[modelRowIndex];
 
         var resolution = this.map.getResolution();
         var deltaY = (prepend) ? -this.tileSize.h : this.tileSize.h;
         var deltaLat = resolution * -deltaY;
 
-        var row = (prepend) ? this.grid.pop() : this.grid.shift();
+        var row = (prepend) ? grid.pop() : grid.shift();
 
         for (var i=0; i < modelRow.length; i++) {
             var modelTile = modelRow[i];
@@ -579,9 +584,9 @@ OpenLayers.Layer.Grid = OpenLayers.Class(OpenLayers.Layer.HTTPRequest, {
         }
 
         if (prepend) {
-            this.grid.unshift(row);
+            grid.unshift(row);
         } else {
-            this.grid.push(row);
+            grid.push(row);
         }
     },
 
@@ -612,9 +617,9 @@ OpenLayers.Layer.Grid = OpenLayers.Class(OpenLayers.Layer.HTTPRequest, {
             var tile = prepend ? this.grid[i].pop() : this.grid[i].shift();
             tile.moveTo(bounds, position);
             if (prepend) {
-                this.grid[i].unshift(tile);
+                row.unshift(tile);
             } else {
-                this.grid[i].push(tile);
+                row.push(tile);
             }
         }
     },