In Sky framework AppView, cache the hit test result for pointer events and...

In Sky framework AppView, cache the hit test result for pointer events and continue using that result until pointerup or pointer cancel event is received

R=abarth@chromium.org, abarth

Review URL: https://codereview.chromium.org/1158933004

sdk/lib/framework/app.dart

@@ -20,21 +20,40 @@ class AppView {
 
   RenderView _renderView;
 
+  Map<int, HitTestResult> _hitTestResultForPointer = new Map<int, HitTestResult>();
+
   RenderBox get root => _renderView.child;
   void set root(RenderBox value) {
     _renderView.child = value;
   }
-
   void _beginFrame(double timeStamp) {
     RenderNode.flushLayout();
     _renderView.paintFrame();
   }
 
   void _handleEvent(sky.Event event) {
-    if (event is! sky.PointerEvent)
-      return;
-    HitTestResult result = new HitTestResult();
-    _renderView.hitTest(result, x: event.x, y: event.y);
+    if (event is sky.PointerEvent)
+      _handlePointerEvent(event);
+  }
+
+  void _handlePointerEvent(sky.PointerEvent event) {
+    HitTestResult result;
+    switch(event.type) {
+      case 'pointerdown':
+        result = new HitTestResult();
+        _renderView.hitTest(result, x: event.x, y: event.y);
+        _hitTestResultForPointer[event.pointer] = result;
+        break;
+      case 'pointerup':
+      case 'pointercancel':
+        result = _hitTestResultForPointer[event.pointer];
+        _hitTestResultForPointer.remove(event.pointer);
+        break;
+      case 'pointermove':
+        result = _hitTestResultForPointer[event.pointer];
+        break;
+    }
+    assert(result != null);
     result.path.reversed.forEach((RenderNode node) {
       node.handlePointer(event);
     });