From 24edce24f1f351e7408475d6b5a74acfde9a7a1d Mon Sep 17 00:00:00 2001
From: Tim Schaub <tim.schaub@gmail.com>
Date: Wed, 26 Sep 2012 12:15:52 +0200
Subject: [PATCH] Add alternate tiles under tiles at target z

When zooming or panning, if we have tiles at alternate resolutions, those tiles are inserted in the DOM before the tiles at the target resolution.  This means you should see blurry tiles instead of whitespace when panning (assuming you've already zoomed in a bit).
---
 src/ol/renderer/dom/tilelayer.js | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/src/ol/renderer/dom/tilelayer.js b/src/ol/renderer/dom/tilelayer.js
index 28687e95d6..65e67e7535 100644
--- a/src/ol/renderer/dom/tilelayer.js
+++ b/src/ol/renderer/dom/tilelayer.js
@@ -248,7 +248,9 @@ ol.renderer.dom.TileLayer.prototype.render = function() {
   goog.array.sort(zs);
 
   var fragment = document.createDocumentFragment();
+  var altFragment = document.createDocumentFragment();
   var newTiles = false;
+  var newAltTiles = false;
   for (var i = 0, ii = zs.length; i < ii; ++i) {
     var tileZ = zs[i];
     var tilesToDraw = tilesToDrawByZ[tileZ];
@@ -269,12 +271,25 @@ ol.renderer.dom.TileLayer.prototype.render = function() {
       if (!(key in this.renderedTiles_)) {
         this.renderedTiles_[key] = tile;
         style.position = 'absolute';
-        goog.dom.appendChild(fragment, img);
-        newTiles = true;
+        if (tileZ === z) {
+          goog.dom.appendChild(fragment, img);
+          newTiles = true;
+        } else {
+          goog.dom.appendChild(altFragment, img);
+          newAltTiles = true;
+        }
       }
     }
   }
 
+  if (newAltTiles) {
+    var child = this.target.firstChild;
+    if (child) {
+      goog.dom.insertSiblingBefore(altFragment, child);
+    } else {
+      goog.dom.appendChild(this.target, altFragment);
+    }
+  }
   if (newTiles) {
     goog.dom.appendChild(this.target, fragment);
   }