Merge pull request #226 from twpayne/preserve-low-resolution-tiles

Preserve low resolution tiles

src/ol/renderer/canvas/canvastilelayerrenderer.js

@@ -199,6 +199,7 @@ ol.renderer.canvas.TileLayer.prototype.renderFrame =
   }
 
   this.updateUsedTiles(frameState.usedTiles, tileSource, z, tileRange);
+  tileSource.useLowResolutionTiles(z, frameState.extent);
   this.scheduleExpireCache(frameState, tileSource);
 
   var transform = this.transform_;

src/ol/renderer/dom/domtilelayerrenderer.js

@@ -217,6 +217,7 @@ ol.renderer.dom.TileLayer.prototype.renderFrame =
   }
 
   this.updateUsedTiles(frameState.usedTiles, tileSource, z, tileRange);
+  tileSource.useLowResolutionTiles(z, frameState.extent);
   this.scheduleExpireCache(frameState, tileSource);
 
 };

src/ol/renderer/layerrenderer.js

@@ -14,7 +14,6 @@ goog.require('ol.TileState');
 goog.require('ol.layer.Layer');
 goog.require('ol.layer.LayerProperty');
 goog.require('ol.layer.LayerState');
-goog.require('ol.source.Source');
 goog.require('ol.source.TileSource');
 
 
@@ -222,24 +221,24 @@ ol.renderer.Layer.prototype.updateAttributions =
 /**
  * @protected
  * @param {Object.<string, Object.<string, ol.TileRange>>} usedTiles Used tiles.
- * @param {ol.source.Source} source Source.
+ * @param {ol.source.TileSource} tileSource Tile source.
  * @param {number} z Z.
  * @param {ol.TileRange} tileRange Tile range.
  */
 ol.renderer.Layer.prototype.updateUsedTiles =
-    function(usedTiles, source, z, tileRange) {
+    function(usedTiles, tileSource, z, tileRange) {
   // FIXME should we use tilesToDrawByZ instead?
-  var sourceKey = goog.getUid(source).toString();
+  var tileSourceKey = goog.getUid(tileSource).toString();
   var zKey = z.toString();
-  if (sourceKey in usedTiles) {
-    if (zKey in usedTiles[sourceKey]) {
-      usedTiles[sourceKey][zKey].extend(tileRange);
+  if (tileSourceKey in usedTiles) {
+    if (zKey in usedTiles[tileSourceKey]) {
+      usedTiles[tileSourceKey][zKey].extend(tileRange);
     } else {
-      usedTiles[sourceKey][zKey] = tileRange;
+      usedTiles[tileSourceKey][zKey] = tileRange;
     }
   } else {
-    usedTiles[sourceKey] = {};
-    usedTiles[sourceKey][zKey] = tileRange;
+    usedTiles[tileSourceKey] = {};
+    usedTiles[tileSourceKey][zKey] = tileRange;
   }
 };
 
@@ -247,15 +246,15 @@ ol.renderer.Layer.prototype.updateUsedTiles =
 /**
  * @protected
  * @param {Object.<string, Object.<string, boolean>>} wantedTiles Wanted tiles.
- * @param {ol.source.Source} source Source.
+ * @param {ol.source.TileSource} tileSource Tile source.
  * @param {ol.TileCoord} tileCoord Tile coordinate.
  */
 ol.renderer.Layer.prototype.updateWantedTiles =
-    function(wantedTiles, source, tileCoord) {
-  var sourceKey = goog.getUid(source).toString();
+    function(wantedTiles, tileSource, tileCoord) {
+  var tileSourceKey = goog.getUid(tileSource).toString();
   var coordKey = tileCoord.toString();
-  if (!(sourceKey in wantedTiles)) {
-    wantedTiles[sourceKey] = {};
+  if (!(tileSourceKey in wantedTiles)) {
+    wantedTiles[tileSourceKey] = {};
   }
-  wantedTiles[sourceKey][coordKey] = true;
+  wantedTiles[tileSourceKey][coordKey] = true;
 };

src/ol/renderer/webgl/webgltilelayerrenderer.js

@@ -459,6 +459,7 @@ ol.renderer.webgl.TileLayer.prototype.renderFrame =
   }
 
   this.updateUsedTiles(frameState.usedTiles, tileSource, z, tileRange);
+  tileSource.useLowResolutionTiles(z, frameState.extent);
   this.scheduleExpireCache(frameState, tileSource);
 
   goog.vec.Mat4.makeIdentity(this.texCoordMatrix_);

src/ol/source/imagetilesource.js

@@ -109,3 +109,14 @@ ol.source.ImageTileSource.prototype.getTile = function(tileCoord) {
 ol.source.ImageTileSource.prototype.getTileCoordUrl = function(tileCoord) {
   return this.tileUrlFunction(tileCoord);
 };
+
+
+/**
+ * @inheritDoc
+ */
+ol.source.ImageTileSource.prototype.useTile = function(tileCoord) {
+  var key = tileCoord.toString();
+  if (this.tileCache_.containsKey(key)) {
+    this.tileCache_.get(key);
+  }
+};

src/ol/source/tilesource.js

@@ -119,3 +119,29 @@ ol.source.TileSource.prototype.getTile = goog.abstractMethod;
 ol.source.TileSource.prototype.getTileGrid = function() {
   return this.tileGrid;
 };
+
+
+/**
+ * @param {number} z Z.
+ * @param {ol.Extent} extent Extent.
+ */
+ol.source.TileSource.prototype.useLowResolutionTiles = function(z, extent) {
+  var tileGrid = this.getTileGrid();
+  var tileRange, x, y, zKey;
+  // FIXME this should loop up to tileGrid's minZ when implemented
+  for (; z >= 0; --z) {
+    tileRange = tileGrid.getTileRangeForExtentAndZ(extent, z);
+    for (x = tileRange.minX; x <= tileRange.maxX; ++x) {
+      for (y = tileRange.minY; y <= tileRange.maxY; ++y) {
+        this.useTile(z + '/' + x + '/' + y);
+      }
+    }
+  }
+};
+
+
+/**
+ * Marks a tile coord as being used, without triggering a load.
+ * @param {string} tileCoordKey Tile coordinate key.
+ */
+ol.source.TileSource.prototype.useTile = goog.nullFunction;