From a05eab29db1497d9e9328856967fb2e5eff9eea9 Mon Sep 17 00:00:00 2001
From: ahocevar <andreas.hocevar@gmail.com>
Date: Tue, 6 Mar 2012 14:40:08 +0100
Subject: [PATCH] Adding tileloadstart event to layer.

For this to be useful (i.e. so listeners can see/modify the tile url), a change in Tile.Image is required so we do not fire the loadstart event before we have the url to load.
---
 lib/OpenLayers/Layer/Grid.js | 4 ++++
 lib/OpenLayers/Tile/Image.js | 9 +++++----
 tests/Layer/Grid.html        | 5 +++--
 3 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/lib/OpenLayers/Layer/Grid.js b/lib/OpenLayers/Layer/Grid.js
index 8a8e74138b..67e47732a3 100644
--- a/lib/OpenLayers/Layer/Grid.js
+++ b/lib/OpenLayers/Layer/Grid.js
@@ -196,6 +196,9 @@ OpenLayers.Layer.Grid = OpenLayers.Class(OpenLayers.Layer.HTTPRequest, {
      * element - {DOMElement} A reference to layer.events.element.
      *
      * Supported event types:
+     * tileloadstart - Triggered when a tile starts loading. Listeners receive
+     *     an object as first argument, which has a tile property that
+     *     references the tile that starts loading.
      * tileloaded - Triggered when each new tile is
      *     loaded, as a means of progress update to listeners.
      *     listeners can access 'numLoadingTiles' if they wish to keep
@@ -971,6 +974,7 @@ OpenLayers.Layer.Grid = OpenLayers.Class(OpenLayers.Layer.HTTPRequest, {
             if (this.numLoadingTiles == 0) {
                 this.events.triggerEvent("loadstart");
             }
+            this.events.triggerEvent("tileloadstart", {tile: tile});
             this.numLoadingTiles++;
         };
       
diff --git a/lib/OpenLayers/Tile/Image.js b/lib/OpenLayers/Tile/Image.js
index e9cff59b5b..b9490c667a 100644
--- a/lib/OpenLayers/Tile/Image.js
+++ b/lib/OpenLayers/Tile/Image.js
@@ -21,9 +21,9 @@
 OpenLayers.Tile.Image = OpenLayers.Class(OpenLayers.Tile, {
 
     /** 
-     * Property: url
+     * APIProperty: url
      * {String} The URL of the image being requested. No default. Filled in by
-     * layer.getURL() function. 
+     * layer.getURL() function. May be modified by loadstart listeners.
      */
     url: null,
     
@@ -166,10 +166,10 @@ OpenLayers.Tile.Image = OpenLayers.Class(OpenLayers.Tile, {
             }
             if (this.isLoading) {
                 //if we're already loading, send 'reload' instead of 'loadstart'.
-                this.events.triggerEvent("reload"); 
+                this._loadEvent = "reload"; 
             } else {
                 this.isLoading = true;
-                this.events.triggerEvent("loadstart");
+                this._loadEvent = "loadstart";
             }
             this.positionTile();
             this.renderTile();
@@ -287,6 +287,7 @@ OpenLayers.Tile.Image = OpenLayers.Class(OpenLayers.Tile, {
      * Creates the content for the frame on the tile.
      */
     initImage: function() {
+        this.events.triggerEvent(this._loadEvent);
         var img = this.getImage();
         if (this.url && img.getAttribute("src") == this.url) {
             this.onImageLoad();
diff --git a/tests/Layer/Grid.html b/tests/Layer/Grid.html
index c07de6c17f..34abdea092 100644
--- a/tests/Layer/Grid.html
+++ b/tests/Layer/Grid.html
@@ -506,7 +506,7 @@
     }  
      
     function test_Layer_Grid_addTileMonitoringHooks(t) {
-        t.plan(17);
+        t.plan(18);
         
         layer = new OpenLayers.Layer.Grid();
         layer.events = {
@@ -546,10 +546,11 @@
 
         t.eq(g_events[0][0], "loadstart", "loadstart event triggered when numLoadingTiles is 0");
         t.eq(layer.numLoadingTiles, 1, "numLoadingTiles incremented");
+        t.eq(g_events[1][0], "tileloadstart", "tileloadstart event triggered");
 
         g_events = [];
         tile.onLoadStart.apply(layer);
-        t.eq(g_events.length, 0, "loadstart event not triggered when numLoadingTiles is not 0");
+        t.eq(g_events.length, 1, "tileloadstart, but not loadstart triggered when numLoadingTiles is not 0");
         t.eq(layer.numLoadingTiles, 2, "numLoadingTiles incremented");