Add support for priority field

index.js

@@ -894,8 +894,19 @@ define(['three'], function(THREE, BSPTree){
 				});
 				return;
 			}
-					
-			if(comparison){
+			
+			if(comparison === 0){
+				var nodePriority = BSPTree.utils.getPriority(node);
+				var compareWithPriority = BSPTree.utils.getPriority(compareWith);
+				
+				if(nodePriority > compareWithPriority){
+					comparison = -1;
+				} else {
+					comparison = 1;
+				}
+			}
+			
+			if(comparison === 1){
                 if(!compareWith.back){
                     compareWith.back = node;
                 } else {
@@ -930,6 +941,13 @@ define(['three'], function(THREE, BSPTree){
 			getPointSign: function(normal, point, pointOnPlane){
 				return this.sign(normal.dot(point.clone().sub(pointOnPlane)));
 			},
+			getPriority: function(node){
+				if(typeof node.element.priority === 'number'){
+					return node.element.priority;
+				} else {
+					return 0;
+				}
+			},
 			isPointInSegment: function(point, p1, p2){
 				// This function assumes that point lies on the line
 				// and determines whether it is in line _segment_
@@ -1004,7 +1022,13 @@ define(['three'], function(THREE, BSPTree){
 			
 			if(thisSign === undefined) return undefined;
 
-			return (viewerSign !== thisSign);
+			if(thisSign === 0) return 0;
+
+			if(viewerSign !== thisSign){
+				return 1;
+			} else {
+				return -1;
+			}
 		}