Adding fractionalZoom property to the map. This allows zooming to an arbitrary level, making it possible to have non-discrete resolutions for layers that support it. This property should not be set to true for layers with fixed zoom levels (commercial layers or others with cached tiles). r=elemoine,crschmidt,ahocevar (closes #1243)

git-svn-id: http://svn.openlayers.org/trunk/openlayers@5982 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Control/Navigation.js

@@ -137,7 +137,7 @@ OpenLayers.Control.Navigation = OpenLayers.Class(OpenLayers.Control, {
         var size    = this.map.getSize();
         var deltaX  = size.w/2 - evt.xy.x;
         var deltaY  = evt.xy.y - size.h/2;
-        var newRes  = this.map.baseLayer.resolutions[newZoom];
+        var newRes  = this.map.baseLayer.getResolutionForZoom(newZoom);
         var zoomPoint = this.map.getLonLatFromPixel(evt.xy);
         var newCenter = new OpenLayers.LonLat(
                             zoomPoint.lon + deltaX * newRes,

lib/OpenLayers/Layer.js

@@ -758,7 +758,7 @@ OpenLayers.Layer = OpenLayers.Class({
      */
     getResolution: function() {
         var zoom = this.map.getZoom();
-        return this.resolutions[zoom];
+        return this.getResolutionForZoom(zoom);
     },
 
     /** 
@@ -812,6 +812,29 @@ OpenLayers.Layer = OpenLayers.Class({
         //to be implemented by subclasses
     },
 
+    /**
+     * APIMethod: getResolutionForZoom
+     * 
+     * Parameter:
+     * zoom - {Float}
+     * 
+     * Returns:
+     * {Float} A suitable resolution for the specified zoom.
+     */
+    getResolutionForZoom: function(zoom) {
+        zoom = Math.max(0, Math.min(zoom, this.resolutions.length - 1));
+        var resolution;
+        if(this.map.fractionalZoom) {
+            var low = Math.floor(zoom);
+            var high = Math.ceil(zoom);
+            resolution = this.resolutions[high] +
+                ((zoom-low) * (this.resolutions[low]-this.resolutions[high]));
+        } else {
+            resolution = this.resolutions[Math.round(zoom)];
+        }
+        return resolution;
+    },
+
     /**
      * APIMethod: getZoomForResolution
      * 
@@ -831,22 +854,50 @@ OpenLayers.Layer = OpenLayers.Class({
      *     value and the 'closest' specification.
      */
     getZoomForResolution: function(resolution, closest) {
-        var diff;
-        var minDiff = Number.POSITIVE_INFINITY;
-        for(var i=0; i < this.resolutions.length; i++) {            
-            if (closest) {
-                diff = Math.abs(this.resolutions[i] - resolution);
-                if (diff > minDiff) {
-                    break;
+        var zoom;
+        if(this.map.fractionalZoom) {
+            var lowZoom = 0;
+            var highZoom = this.resolutions.length - 1;
+            var highRes = this.resolutions[lowZoom];
+            var lowRes = this.resolutions[highZoom];
+            var res;
+            for(var i=0; i<this.resolutions.length; ++i) {
+                res = this.resolutions[i];
+                if(res >= resolution) {
+                    highRes = res;
+                    lowZoom = i;
                 }
-                minDiff = diff;
-            } else {
-                if (this.resolutions[i] < resolution) {
+                if(res <= resolution) {
+                    lowRes = res;
+                    highZoom = i;
                     break;
                 }
             }
+            var dRes = highRes - lowRes;
+            if(dRes > 0) {
+                zoom = lowZoom + ((resolution - lowRes) / dRes);
+            } else {
+                zoom = lowZoom;
+            }
+        } else {
+            var diff;
+            var minDiff = Number.POSITIVE_INFINITY;
+            for(var i=0; i < this.resolutions.length; i++) {            
+                if (closest) {
+                    diff = Math.abs(this.resolutions[i] - resolution);
+                    if (diff > minDiff) {
+                        break;
+                    }
+                    minDiff = diff;
+                } else {
+                    if (this.resolutions[i] < resolution) {
+                        break;
+                    }
+                }
+            }
+            zoom = Math.max(0, i-1);
         }
-        return Math.max(0, i-1);
+        return zoom;
     },
     
     /**

lib/OpenLayers/Map.js

@@ -66,6 +66,14 @@ OpenLayers.Map = OpenLayers.Class({
      */
     id: null,
     
+    /**
+     * Property: fractionalZoom
+     * {Boolean} For a base layer that supports it, allow the map resolution
+     *     to be set to a value between one of the values in the resolutions
+     *     array.  Default is false.
+     */
+    fractionalZoom: false,
+    
     /**
      * APIProperty: events
      * {<OpenLayers.Events>} An events object that handles all 
@@ -1266,10 +1274,7 @@ OpenLayers.Map = OpenLayers.Class({
             if(zoom == null) { 
                 zoom = this.getZoom(); 
             }
-            var resolution = null;
-            if(this.baseLayer != null) {
-                resolution = this.baseLayer.resolutions[zoom];
-            }
+            var resolution = this.getResolutionForZoom(zoom);
             var extent = this.calculateBounds(lonlat, resolution); 
             if(!this.restrictedExtent.containsBounds(extent)) {
                 var maxCenter = this.restrictedExtent.getCenterLonLat(); 
@@ -1326,7 +1331,7 @@ OpenLayers.Map = OpenLayers.Class({
 
             if (zoomChanged) {
                 this.zoom = zoom;
-                this.resolution = this.baseLayer.getResolution();
+                this.resolution = this.getResolutionForZoom(zoom);
                 // zoom level has changed, increment viewRequestID.
                 this.viewRequestID++;
             }    
@@ -1594,6 +1599,24 @@ OpenLayers.Map = OpenLayers.Class({
         return zoom;
     },
 
+    /**
+     * APIMethod: getResolutionForZoom
+     * 
+     * Parameter:
+     * zoom - {Float}
+     * 
+     * Returns:
+     * {Float} A suitable resolution for the specified zoom.  If no baselayer
+     *     is set, returns null.
+     */
+    getResolutionForZoom: function(zoom) {
+        var resolution = null;
+        if(this.baseLayer) {
+            resolution = this.baseLayer.getResolutionForZoom(zoom);
+        }
+        return resolution;
+    },
+
     /**
      * APIMethod: getZoomForResolution
      *