Layer and tile API update.

The tile now has responsibility for resolving feature ids and fetching feature data given x, y pixel offsets with getFeatureId and getFeatureData methods.  The layer has corresponding getFeatureId and getFeatureData methods that take a map location, lookup the appropriate tile, and delegate to the tile for the rest of the work.

lib/OpenLayers/Control/UTFGrid.js

@@ -180,7 +180,7 @@ OpenLayers.Control.UTFGrid = OpenLayers.Class(OpenLayers.Control, {
             for (var i=0, len=layers.length; i<len; i++) {
                 layer = layers[i];
                 idx = this.map.layers.indexOf(layer);
-                dataLookup[idx] = layer.getData(lonLat);
+                dataLookup[idx] = layer.getFeatureData(lonLat);
             }
             this.callback(dataLookup); // perhaps pass tile, lonLat?
         }

lib/OpenLayers/Layer/UTFGrid.js

@@ -107,6 +107,9 @@ OpenLayers.Layer.UTFGrid = OpenLayers.Class(OpenLayers.Layer.Grid, {
      */
     initialize: function(name, url, options) {
         OpenLayers.Layer.Grid.prototype.initialize.apply(this, [name, url, {}, options]);
+        this.tileOptions = OpenLayers.Util.extend({
+            utfgridResolution: this.utfgridResolution
+        }, this.tileOptions);
     },
 
     /**
@@ -158,10 +161,12 @@ OpenLayers.Layer.UTFGrid = OpenLayers.Class(OpenLayers.Layer.Grid, {
 
     /**
      * APIProperty: utfgridResolution
-     * {Number} Number of pixels per grid "cell"
-     * Defaults to 4
+     * {Number}
+     * Ratio of the pixel width to the width of a UTFGrid data point.  If an 
+     *     entry in the grid represents a 2x2 block of pixels, the 
+     *     utfgridResolution would be 2.  Default is 4 (specified in 
+     *     <OpenLayers.Tile.UTFGrid>).
      */
-    utfgridResolution: 4,
 
     /** 
      * Method: getTileInfo
@@ -232,50 +237,41 @@ OpenLayers.Layer.UTFGrid = OpenLayers.Class(OpenLayers.Layer.Grid, {
     },
 
     /**
-     * APIProperty: getData
-     * Get tile data associated with a map location.
+     * APIProperty: getFeatureData
+     * Get feature data from UTFGrid associated with a map location.
      *
      * Parameters:
      * location - {<OpenLayers.LonLat>} map location
      *
      * Returns:
      * {Object} The UTFGrid data corresponding to the given map location.
      */
-    getData: function(location) {
-        var info = this.getTileInfo(location);
-        var tile = info.tile;
+    getFeatureData: function(location) {
         var data;
-        if (tile) {
-            var resolution = this.utfgridResolution;
-            var json = tile.json
-            if (json) {
-                var code = this.resolveCode(json.grid[ 
-                        Math.floor((info.j) / resolution) 
-                    ].charCodeAt(
-                        Math.floor((info.i) / resolution)
-                    ));
-                data = json.data[json.keys[code]];
-            }
+        var info = this.getTileInfo(location);
+        if (info.tile) {
+            data = info.tile.getFeatureData(info.i, info.j);
         }
         return data;
     },
 
     /**
-     * Method: resolveCode
-     * Resolve the UTF-8 encoding stored in grids to simple number values.  
-     *     See the UTFGrid spec for details.
+     * APIMethod: getFeatureId
+     * Get the identifier for the feature associated with a map location.
      *
      * Parameters:
-     * key - {Integer}
+     * location - {<OpenLayers.LonLat>} map location
      *
      * Returns:
-     * {Integer} Adjusted key for non-escaped chars
+     * {Object} The feature identifier corresponding to the given map location.
      */
-    resolveCode: function(key) {
-        if (key >= 93) key--;
-        if (key >= 35) key--;
-        key -= 32;
-        return key;
+    getFeatureId: function(location) {
+        var id;
+        var info = this.getTileInfo(location);
+        if (info.tile) {
+            id = info.tile.getFeatureId(info.i, info.j);
+        }
+        return id;
     },
 
     /**

lib/OpenLayers/Tile/UTFGrid.js

@@ -32,6 +32,15 @@ OpenLayers.Tile.UTFGrid = OpenLayers.Class(OpenLayers.Tile, {
      */
     url: null,
 
+    /**
+     * Property: utfgridResolution
+     * {Number}
+     * Ratio of the pixel width to the width of a UTFGrid data point.  If an 
+     *     entry in the grid represents a 2x2 block of pixels, the 
+     *     utfgridResolution would be 2.  Default is 4.
+     */
+    utfgridResolution: 4,
+
     /** 
      * Property: json
      * {Object}
@@ -135,6 +144,68 @@ OpenLayers.Tile.UTFGrid = OpenLayers.Class(OpenLayers.Tile, {
         }
         this.isLoading = false;
     },
+
+    /**
+     * Method: getFeatureData
+     * Get feature data associated with a pixel offset.
+     *
+     * Parameters:
+     * i - {Number} X-axis pixel offset (from top left of tile)
+     * j - {Number} Y-axis pixel offset (from top left of tile)
+     *
+     * Returns:
+     * {Object} The UTFGrid data corresponding to the given pixel offset.
+     */
+    getFeatureData: function(i, j) {
+        var data;
+        if (this.json) {
+            data = this.json.data[this.getFeatureId(i, j)];
+        }
+        return data;
+    },
+
+    /**
+     * Method: getFeatureId
+     * Get the identifier for the feature associated with a pixel offset.
+     *
+     * Parameters:
+     * i - {Number} X-axis pixel offset (from top left of tile)
+     * j - {Number} Y-axis pixel offset (from top left of tile)
+     *
+     * Returns:
+     * {Object} The feature identifier corresponding to the given pixel offset.
+     */
+    getFeatureId: function(i, j) {
+        var id;
+        if (this.json) {
+            var resolution = this.utfgridResolution;
+            var code = this.resolveCode(this.json.grid[ 
+                    Math.floor((j) / resolution) 
+                ].charCodeAt(
+                    Math.floor((i) / resolution)
+                ));
+            id = this.json.keys[code];
+        }
+        return id;
+    },
+
+    /**
+     * Method: resolveCode
+     * Resolve the UTF-8 encoding stored in grids to simple number values.  
+     *     See the UTFGrid spec for details.
+     *
+     * Parameters:
+     * key - {Integer}
+     *
+     * Returns:
+     * {Integer} Adjusted key for non-escaped chars
+     */
+    resolveCode: function(key) {
+        if (key >= 93) key--;
+        if (key >= 35) key--;
+        key -= 32;
+        return key;
+    },
 
     /**
      * Method: parseData

tests/Tile/UTFGrid.html

@@ -15,7 +15,7 @@
             projection: "EPSG:900913",
             layers: [layer],
             center: [0, 0],
-            zoom: 0
+            zoom: 1
         });
     }
 
@@ -158,6 +158,42 @@
         });
 
     }
+
+    function test_getFeatureId(t) {
+        t.plan(3);
+        setUp();
+
+        var tile = layer.grid[1][1];
+        t.delay_call(0.5, function() {
+            var id = tile.getFeatureId(16, 60);
+            t.eq(id, "238", "feature 238 at 16, 60");
+            t.eq(tile.getFeatureId(18, 63), id, "same feature at 18, 63");
+
+            t.eq(tile.getFeatureId(300, 10), undefined, "undefined id outside tile");
+
+            tearDown();
+        });
+    }
+
+    function test_getFeatureData(t) {
+        t.plan(3);
+        setUp();
+
+        var tile = layer.grid[1][1];
+        t.delay_call(0.5, function() {
+            var data = tile.getFeatureData(16, 60);
+            var exp = {
+                NAME: "Svalbard",
+                POP2005: 0
+            };
+            t.eq(data, exp, "feature data at 16, 60");
+            t.eq(tile.getFeatureData(17, 62), exp, "same feature at 17, 62");
+
+            t.eq(tile.getFeatureData(300, 10), undefined, "undefined data outside tile");
+
+            tearDown();
+        });
+    }
 
   </script>
 </head>