From 36c80f61bccc13fd245c41263941732e4f98cb56 Mon Sep 17 00:00:00 2001
From: Andreas Hocevar <andreas.hocevar@gmail.com>
Date: Wed, 28 Jun 2017 23:16:11 +0200
Subject: [PATCH 1/2] Do not delete tile keys for error or empty tiles

---
 src/ol/vectorimagetile.js | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/src/ol/vectorimagetile.js b/src/ol/vectorimagetile.js
index ed7db45da6..1ad0aeecac 100644
--- a/src/ol/vectorimagetile.js
+++ b/src/ol/vectorimagetile.js
@@ -244,17 +244,18 @@ ol.VectorImageTile.prototype.load = function() {
  */
 ol.VectorImageTile.prototype.finishLoading_ = function() {
   var errors = false;
-  var tile;
-  for (var i = this.tileKeys.length - 1; i >= 0; --i) {
-    tile = this.getTile(this.tileKeys[i]);
-    if (tile.getState() == ol.TileState.ERROR) {
-      errors = true;
-    }
-    if (tile.getState() != ol.TileState.LOADED) {
-      this.tileKeys.splice(i, 1);
+  var loaded = this.tileKeys.length;
+  var state;
+  for (var i = loaded - 1; i >= 0; --i) {
+    state = this.getTile(this.tileKeys[i]).getState();
+    if (state != ol.TileState.LOADED) {
+      if (state == ol.TileState.ERROR) {
+        errors = true;
+      }
+      --loaded;
     }
   }
-  this.setState(this.tileKeys.length > 0 ?
+  this.setState(loaded > 0 ?
     ol.TileState.LOADED :
     (errors ? ol.TileState.ERROR : ol.TileState.EMPTY));
 };

From 970265acb002f19592e33b9d1ed9900dc571c9d4 Mon Sep 17 00:00:00 2001
From: Andreas Hocevar <andreas.hocevar@gmail.com>
Date: Thu, 29 Jun 2017 00:02:24 +0200
Subject: [PATCH 2/2] Give preloaded lower resolution tiles a chance to display
 immediately

---
 src/ol/renderer/canvas/tilelayer.js | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/src/ol/renderer/canvas/tilelayer.js b/src/ol/renderer/canvas/tilelayer.js
index 2f3695d510..2fb975e72c 100644
--- a/src/ol/renderer/canvas/tilelayer.js
+++ b/src/ol/renderer/canvas/tilelayer.js
@@ -144,9 +144,14 @@ ol.renderer.canvas.TileLayer.prototype.prepareFrame = function(frameState, layer
   for (x = tileRange.minX; x <= tileRange.maxX; ++x) {
     for (y = tileRange.minY; y <= tileRange.maxY; ++y) {
       tile = tileSource.getTile(z, x, y, pixelRatio, projection);
-      // When useInterimTilesOnError is false, we consider the error tile as loaded.
-      if (tile.getState() == ol.TileState.ERROR && !this.getLayer().getUseInterimTilesOnError()) {
-        tile.setState(ol.TileState.LOADED);
+      if (tile.getState() == ol.TileState.ERROR) {
+        if (!tileLayer.getUseInterimTilesOnError()) {
+          // When useInterimTilesOnError is false, we consider the error tile as loaded.
+          tile.setState(ol.TileState.LOADED);
+        } else if (tileLayer.getPreload() > 0) {
+          // Preloaded tiles for lower resolutions might have finished loading.
+          newTiles = true;
+        }
       }
       if (!this.isDrawableTile_(tile)) {
         tile = tile.getInterimTile();