From f9ae12f2271adf4422da33f4dc9797d61d24e89f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=89ric=20Lemoine?= <eric.lemoine@gmail.com>
Date: Wed, 19 Oct 2011 20:42:34 +0200
Subject: [PATCH] minor refactoring in Layer.Grid - add a removeBackBuffer
 function

---
 lib/OpenLayers/Layer/Grid.js | 35 +++++++++++++++++++++++------------
 1 file changed, 23 insertions(+), 12 deletions(-)

diff --git a/lib/OpenLayers/Layer/Grid.js b/lib/OpenLayers/Layer/Grid.js
index fd13b1aabb..fc2232a6a8 100644
--- a/lib/OpenLayers/Layer/Grid.js
+++ b/lib/OpenLayers/Layer/Grid.js
@@ -462,7 +462,7 @@ OpenLayers.Layer.Grid = OpenLayers.Class(OpenLayers.Layer.HTTPRequest, {
                         return;
                     }
                     // to be able to correctly position the back buffer we
-                    // place the first tile at (0, 0) in the back buffer
+                    // place the tiles grid at (0, 0) in the back buffer
                     tile.style.left = (j * this.tileSize.w) + '%';
                     tile.style.top = (i * this.tileSize.h) + '%';
                     backBuffer.appendChild(tile);
@@ -472,15 +472,31 @@ OpenLayers.Layer.Grid = OpenLayers.Class(OpenLayers.Layer.HTTPRequest, {
         return backBuffer;
     },
 
+    /**
+     * Method: removeBackBuffer
+     * Remove back buffer from DOM.
+     */
+    removeBackBuffer: function() {
+        if(this.backBuffer && this.backBuffer.parentNode) {
+            this.div.removeChild(this.backBuffer);
+            this.backBuffer = null;
+        }
+    },
+
     /**
      * Method: updateBackBufferData
      * Upstate states in the backBufferData property
      */
     updateBackBufferData: function() {
-        this.backBufferData.resolution = this.getServerResolution();
-        var topLeftTile = this.grid[0][0];
-        this.backBufferData.lonlat = {lon: topLeftTile.bounds.left,
-                                      lat: topLeftTile.bounds.top};
+        // updateBackBufferData is called asynchronously when tiles are
+        // received, so we need to check that the map is still there
+        if (this.map) {
+            var resolution = this.map.getResolution();
+            this.backBufferData.resolution = this.getServerResolution(resolution);
+            var topLeftTile = this.grid[0][0];
+            this.backBufferData.lonlat = {lon: topLeftTile.bounds.left,
+                                          lat: topLeftTile.bounds.top};
+        }
     },
 
     /**
@@ -902,13 +918,8 @@ OpenLayers.Layer.Grid = OpenLayers.Class(OpenLayers.Layer.HTTPRequest, {
             //if that was the last tile, then trigger a 'loadend' on the layer
             if (this.numLoadingTiles == 0) {
                 this.events.triggerEvent("loadend");
-                if(this.backBuffer && this.backBuffer.parentNode) {
-                    this.div.removeChild(this.backBuffer);
-                    this.backBuffer = null;
-                }
-                if(this.map) {
-                    this.updateBackBufferData();
-                }
+                this.removeBackBuffer();
+                this.updateBackBufferData();
             }
         };
         tile.events.register("loadend", this, tile.onLoadEnd);