First pass at alt-tile rendering for dom renderer

src/ol/renderer/dom/tilelayer.js

@@ -1,6 +1,10 @@
 goog.provide('ol.renderer.dom.TileLayer');
 
+goog.require('goog.asserts');
 goog.require('goog.dom');
+goog.require('goog.events');
+goog.require('goog.events.Event');
+goog.require('goog.events.EventType');
 goog.require('ol.Coordinate');
 goog.require('ol.Extent');
 goog.require('ol.renderer.dom.Layer');
@@ -28,6 +32,26 @@ ol.renderer.dom.TileLayer = function(mapRenderer, tileLayer, target) {
    * @private
    */
   this.renderedMapResolution_ = undefined;
+
+  /**
+   * @type {number|undefined}
+   * @private
+   */
+  this.renderedTileRange_ = undefined;
+
+  /**
+   * @type {number|undefined}
+   * @private
+   */
+  this.renderedZ_ = undefined;
+
+  /**
+   * Map of tile keys loading at the currently rendered z.
+   * @type {Object.<sring, ol.Tile>}
+   * @private
+   */
+  this.loadingTiles_ = {};
+
 };
 goog.inherits(ol.renderer.dom.TileLayer, ol.renderer.dom.Layer);
 
@@ -63,11 +87,10 @@ ol.renderer.dom.TileLayer.prototype.getTileOffset_ = function(z, resolution) {
 /**
  * Get rid of tiles outside the rendered extent.
  * @private
- * @param {ol.TileRange} tileRange Tile range.
- * @param {number} z Z.
  */
-ol.renderer.dom.TileLayer.prototype.removeInvisibleTiles_ = function(
-    tileRange, z) {
+ol.renderer.dom.TileLayer.prototype.removeInvisibleTiles_ = function() {
+  var tileRange = this.renderedTileRange_;
+  var z = this.renderedZ_;
   var key, tileCoord, prune, tile;
   for (key in this.renderedTiles_) {
     tileCoord = ol.TileCoord.createFromString(key);
@@ -85,6 +108,30 @@ ol.renderer.dom.TileLayer.prototype.removeInvisibleTiles_ = function(
 };
 
 
+/**
+ * @param {goog.events.Event} event Tile change event.
+ * @private
+ */
+ol.renderer.dom.TileLayer.prototype.handleTileChange_ = function(event) {
+  var tile = event.target;
+  goog.asserts.assert(tile.getState() == ol.TileState.LOADED);
+  var tileCoord = tile.tileCoord;
+  if (tileCoord.z === this.renderedZ_) {
+    var key = tileCoord.toString();
+    delete this.loadingTiles_[key];
+    // determine if we've fully loaded this zoom level
+    var loaded = true;
+    for (key in this.loadingTiles_) {
+      loaded = false;
+      break;
+    }
+    if (loaded) {
+      this.removeInvisibleTiles_();
+    }
+  }
+};
+
+
 /**
  * @inheritDoc
  */
@@ -101,48 +148,119 @@ ol.renderer.dom.TileLayer.prototype.render = function() {
   var tileStore = tileLayer.getStore();
   var tileGrid = tileStore.getTileGrid();
 
-  if (mapResolution != this.renderedMapResolution_) {
-    this.renderedTiles_ = {};
-    goog.dom.removeChildren(this.target);
-  }
-
   // z represents the "best" resolution
   var z = tileGrid.getZForResolution(mapResolution);
 
+  if (z != this.renderedZ_) {
+    // no longer wait for previously loading tiles
+    this.loadingTiles_ = {};
+  }
+
+  /**
+   * @type {Object.<number, Object.<string, ol.Tile>>}
+   */
+  var tilesToDrawByZ = {};
+  tilesToDrawByZ[z] = {};
+
   var tileRange =
       tileGrid.getTileRangeForExtentAndResolution(mapExtent, mapResolution);
-  var tileOffset = this.getTileOffset_(z, mapResolution);
+
+
+  // first pass through the tile range to determine all the tiles needed
+  var allTilesLoaded = true;
+  tileRange.forEachTileCoord(z, function(tileCoord) {
+
+    var tile = tileStore.getTile(tileCoord);
+    if (goog.isNull(tile)) {
+      // we're outside the store's extent, continue
+      return;
+    }
+
+    var key = tile.tileCoord.toString();
+    if (tile.getState() == ol.TileState.LOADED) {
+      tilesToDrawByZ[z][key] = tile;
+      return;
+    } else {
+      if (!(key in this.loadingTiles_)) {
+        goog.events.listen(tile, goog.events.EventType.CHANGE,
+            this.handleTileChange_, false, this);
+        this.loadingTiles_[key] = tile;
+        allTilesLoaded = false;
+        tile.load();
+      }
+      // TODO: only append after load?
+      tilesToDrawByZ[z][key] = tile;
+    }
+
+    /**
+     * Look for already loaded tiles that can serve as placeholders.
+     */
+    // FIXME this could be more efficient about filling partial holes
+    tileGrid.forEachTileCoordParentTileRange(
+        tileCoord,
+        function(altZ, altTileRange) {
+          var fullyCovered = true;
+          altTileRange.forEachTileCoord(altZ, function(altTileCoord) {
+            var tileKey = altTileCoord.toString();
+            if (tilesToDrawByZ[altZ] && tilesToDrawByZ[altZ][tileKey]) {
+              return;
+            }
+            var altTile = tileStore.getTile(altTileCoord);
+            if (!goog.isNull(altTile) &&
+                altTile.getState() == ol.TileState.LOADED) {
+              if (!(altZ in tilesToDrawByZ)) {
+                tilesToDrawByZ[altZ] = {};
+              }
+              tilesToDrawByZ[altZ][tileKey] = altTile;
+            } else {
+              fullyCovered = false;
+            }
+          });
+          return fullyCovered;
+        });
+
+  }, this);
+
+  /** @type {Array.<number>} */
+  var zs = goog.object.getKeys(tilesToDrawByZ);
+  goog.array.sort(zs);
 
   var fragment = document.createDocumentFragment();
-
-  var key, tile, pixelBounds, img, newTiles = false;
-  tileRange.forEachTileCoord(z, function(tileCoord) {
-    key = tileCoord.toString();
-    tile = this.renderedTiles_[key];
-    if (!goog.isDef(tile)) {
-      tile = tileStore.getTile(tileCoord);
-      if (goog.isNull(tile)) {
-      } else {
-        tile.load();
+  var newTiles = false;
+  for (var i = 0, ii = zs.length; i < ii; ++i) {
+    var tileZ = zs[i];
+    var tilesToDraw = tilesToDrawByZ[tileZ];
+    var tileOffset = this.getTileOffset_(tileZ, mapResolution);
+    for (var key in tilesToDraw) {
+      var tile = tilesToDraw[key];
+      var tileCoord = tile.tileCoord;
+      var pixelBounds = tileGrid.getPixelBoundsForTileCoordAndResolution(
+          tileCoord, mapResolution);
+      var img = tile.getImage(this);
+      var style = img.style;
+      // TODO: use translate method
+      style.left = (pixelBounds.minX - tileOffset.x) + 'px';
+      style.top = (-pixelBounds.maxY - tileOffset.y) + 'px';
+      style.width = pixelBounds.getWidth() + 'px';
+      style.height = pixelBounds.getHeight() + 'px';
+      if (!(key in this.renderedTiles_)) {
         this.renderedTiles_[key] = tile;
-        pixelBounds = tileGrid.getPixelBoundsForTileCoordAndResolution(
-            tileCoord, mapResolution);
-        img = tile.getImage(this);
-        img.style.position = 'absolute';
-        img.style.left = (pixelBounds.minX - tileOffset.x) + 'px';
-        img.style.top = (-pixelBounds.maxY - tileOffset.y) + 'px';
-        img.style.width = pixelBounds.getWidth() + 'px';
-        img.style.height = pixelBounds.getHeight() + 'px';
+        style.position = 'absolute';
         goog.dom.appendChild(fragment, img);
         newTiles = true;
       }
     }
-  }, this);
+  }
 
   if (newTiles) {
     goog.dom.appendChild(this.target, fragment);
   }
 
-  this.removeInvisibleTiles_(tileRange, z);
+  if (allTilesLoaded) {
+    this.removeInvisibleTiles_();
+  }
+
+  this.renderedTileRange_ = tileRange;
+  this.renderedZ_ = z;
   this.renderedMapResolution_ = mapResolution;
 };