added support for text labels. This also adds getCentroid methods to all

geometries. Thanks crschmidt for the great help with this patch, and 
thanks to camptocamp for the initial work on this and rcoup for creating 
the first patches. r=crschmidt (closes #1895)


git-svn-id: http://svn.openlayers.org/trunk/openlayers@9262 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Renderer.js

@@ -176,7 +176,13 @@ OpenLayers.Renderer = OpenLayers.Class({
                 if (!bounds.intersectsBounds(this.extent)) {
                     style = {display: "none"};
                 }
-                return this.drawGeometry(feature.geometry, style, feature.id);
+                var rendered = this.drawGeometry(feature.geometry, style, feature.id);
+                if(style.display != "none" && style.label && rendered !== false) {
+                    this.drawText(feature.id, style, feature.geometry.getCentroid());
+                } else {
+                    this.removeText(feature.id);
+                }
+                return rendered;
             }
         }
     },
@@ -196,6 +202,28 @@ OpenLayers.Renderer = OpenLayers.Class({
      */
     drawGeometry: function(geometry, style, featureId) {},
         
+    /**
+     * Method: drawText
+     * Function for drawing text labels.
+     * This method is only called by the renderer itself.
+     * 
+     * Parameters: 
+     * featureId - {String}
+     * style -
+     * location - {<OpenLayers.Geometry.Point>}
+     */
+    drawText: function(featureId, style, location) {},
+
+    /**
+     * Method: removeText
+     * Function for removing text labels.
+     * This method is only called by the renderer itself.
+     * 
+     * Parameters: 
+     * featureId - {String}
+     */
+    removeText: function(featureId) {},
+    
     /**
      * Method: clear
      * Clear all vectors from the renderer.
@@ -231,6 +259,7 @@ OpenLayers.Renderer = OpenLayers.Class({
         }
         for(var i=0, len=features.length; i<len; ++i) {
             this.eraseGeometry(features[i].geometry);
+            this.removeText(features[i].id);
         }
     },