cleaned up intersects logic, and added more docs

src/Shape.js

@@ -306,6 +306,7 @@ Kinetic.Shape = Kinetic.Node.extend({
         var pos = Kinetic.Type._getXY(Array.prototype.slice.call(arguments));
         var stage = this.getStage();
 
+        // path detection
         if(this.attrs.detectionType === 'path') {
             var pathLayer = stage.pathLayer;
             var pathLayerContext = pathLayer.getContext();
@@ -314,11 +315,16 @@ Kinetic.Shape = Kinetic.Node.extend({
 
             return pathLayerContext.isPointInPath(pos.x, pos.y);
         }
-        else {
+
+        // pixel detection
+        if(this.imageData) {
             var w = stage.attrs.width;
             var alpha = this.imageData.data[((w * pos.y) + pos.x) * 4 + 3];
-            return (!!alpha);
+            return (alpha);
         }
+
+        // default
+        return false;
     },
     _draw: function(layer) {
         if(layer && this.attrs.drawFunc) {