Sprites correctly handles zPosition

sky/examples/game/lib/sprite_box.dart

 part of sprites;
 
 enum SpriteBoxTransformMode {
   nativePoints,
   letterbox,
   stretch,
   scaleToFit,
   fixedWidth,
   fixedHeight,
 }
@@ skipping 56 matching lines @@
 
   void performLayout() {
     size = constraints.constrain(Size.infinite);
     _invalidateTransformMatrix();
     _callSpriteBoxPerformedLayout(_rootNode);
   }
 
   // Event handling
 
   void _addEventTargets(Node node, List<Node> eventTargets) {
+    List children = node.children;
+    int i = 0;
+
+    // Add childrens that are behind this node
+    while (i < children.length) {
+      Node child = children[i];
+      if (child.zPosition >= 0.0) break;
+      _addEventTargets(child, eventTargets);
+      i++;
+    }
+
+    // Add this node
     if (node.userInteractionEnabled) {
       eventTargets.add(node);
     }
-    for (Node child in node.children) {
+
+    // Add children in front of this node
+    while (i < children.length) {
+      Node child = children[i];
       _addEventTargets(child, eventTargets);
+      i++;
     }
   }
 
   void handleEvent(Event event, SpriteBoxHitTestEntry entry) {
     if (event is PointerEvent) {
 
       if (event.type == 'pointerdown') {
         // Build list of event targets
         if (_eventTargets == null) {
           _eventTargets = [];
           _addEventTargets(_rootNode, _eventTargets);
         }
 
         // Find the once that are hit by the pointer
         List<Node> nodeTargets = [];
         for (int i = _eventTargets.length - 1; i >= 0; i--) {
           Node node = _eventTargets[i];
 
           // Check if the node is ready to handle a pointer
           if (node.handleMultiplePointers || node._handlingPointer == null) {
             // Do the hit test
             Point posInNodeSpace = node.convertPointToNodeSpace(entry.localPosition);
-            if (node.hitTest(posInNodeSpace)) {
+            if (node.isPointInside(posInNodeSpace)) {
               nodeTargets.add(node);
               node._handlingPointer = event.pointer;
             }
           }
         }
 
         entry.nodeTargets = nodeTargets;
       }
 
       // Pass the event down to nodes that were hit by the pointerdown
@@ skipping 99 matching lines @@
     _rootNode._invalidateToBoxTransformMatrix();
   }
 
   void paint(RenderObjectDisplayList canvas) {
     canvas.save();
 
     // Move to correct coordinate space before drawing
     canvas.concat(transformMatrix.storage);
 
     // Draw the sprite tree
-    _rootNode.visit(canvas);
+    _rootNode._visit(canvas);
 
     canvas.restore();
   }
 
   // Updates
 
   int _animationId = 0;
 
   void _scheduleTick() {
     _animationId = scheduler.requestAnimationFrame(_tick);
@@ skipping 47 matching lines @@
     return nodes;
   }
 
   _addNodesAtPosition(Node node, Point position, List<Node> list) {
     // Visit children first
     for (Node child in node.children) {
       _addNodesAtPosition(child, position, list);
     }
     // Do the hit test
     Point posInNodeSpace = node.convertPointToNodeSpace(position);
-    if (node.hitTest(posInNodeSpace)) {
+    if (node.isPointInside(posInNodeSpace)) {
       list.add(node);
     }
   }
 }
 
 class SpriteBoxHitTestEntry extends BoxHitTestEntry {
   List<Node> nodeTargets;
   SpriteBoxHitTestEntry(RenderBox target, Point localPosition) : super(target, localPosition);
 }
 
 class SpriteBoxEvent {
   Point boxPosition;
   String type;
   int pointer;
 
   SpriteBoxEvent(this.boxPosition, this.type, this.pointer);
 }