Makes event dispatch implicitly target specific window until release

components/mus/ws/event_dispatcher.h

Index: components/mus/ws/event_dispatcher.h
diff --git a/components/mus/ws/event_dispatcher.h b/components/mus/ws/event_dispatcher.h
index 0e89233572769c5dcadf0273fcc7798e172bf1c1..bbd2badce05cc8188c60cb9e6f660d5cc5e29568 100644
--- a/components/mus/ws/event_dispatcher.h
+++ b/components/mus/ws/event_dispatcher.h
@@ -13,6 +13,7 @@
 #include "components/mus/public/interfaces/input_event_matcher.mojom.h"
 #include "components/mus/public/interfaces/input_events.mojom.h"
 #include "components/mus/public/interfaces/input_key_codes.mojom.h"
+#include "components/mus/ws/server_window_observer.h"
 #include "ui/gfx/geometry/rect_f.h"
 
 namespace mus {
@@ -23,10 +24,10 @@ class EventMatcher;
 class ServerWindow;
 
 // Handles dispatching events to the right location as well as updating focus.
-class EventDispatcher {
+class EventDispatcher : public ServerWindowObserver {
  public:
   explicit EventDispatcher(EventDispatcherDelegate* delegate);
-  ~EventDispatcher();
+  ~EventDispatcher() override;
 
   void set_root(ServerWindow* root) { root_ = root; }
 
@@ -38,29 +39,67 @@ class EventDispatcher {
   void OnEvent(mojom::EventPtr event);
 
  private:
+  // Keeps track of state associated with a pointer down until the
+  // corresponding up/cancel.
+  struct PointerTarget {
+    PointerTarget() : window(nullptr), in_nonclient_area(false) {}
+
+    // NOTE: this is set to null if the window is destroyed before a
+    // corresponding release/cancel.
+    ServerWindow* window;
+
+    // Did the pointer event start in the non-client area.
+    bool in_nonclient_area;
+  };
+
+  void ProcessKeyEvent(mojom::EventPtr event);
+
+  // EventDispatcher provides the following logic for pointer events:
+  // . wheel events go to the current target of the associated pointer. If
+  //   there is no target, they go to the deepest window.
+  // . move (not drag) events go to the deepest window.
+  // . when a pointer goes down all events until the corresponding up or
+  //   cancel go to the deepest target. For mouse events the up only occurs
+  //   when no buttons on the mouse are down.
+  void ProcessPointerEvent(mojom::EventPtr event);
+
+  // If |target->window| is valid, then passes the event to the delegate.
+  void DispatchToPointerTarget(const PointerTarget& target,
+                               mojom::EventPtr event);
+
+  // Stops sending pointer events to |window|. This does not remove the entry
+  // for |window| from |pointer_targets_|, rather it nulls out the window. This
+  // way we continue to eat events until the up/cancel is received.
+  void CancelPointerEventsToTarget(ServerWindow* window);
+
+  // Returns true if we're currently an observer for |window|. We are an
+  // observer for a window if any pointer events are targeting it.
+  bool IsObservingWindow(ServerWindow* window);
+
   // Looks to see if there is an accelerator bound to the specified code/flags.
   // If there is one, sets |accelerator_id| to the id of the accelerator invoked
   // and returns true. If there is none, returns false so normal key event
   // processing can continue.
   bool FindAccelerator(const mojom::Event& event, uint32_t* accelerator_id);
 
-  // Returns the ServerWindow that should receive |event|. If |event| is a
-  // pointer-type event, then this function also updates the event location to
-  // make sure it is in the returned target's coordinate space.
-  ServerWindow* FindEventTarget(mojom::Event* event);
+  // ServerWindowObserver:
+  void OnWillChangeWindowHierarchy(ServerWindow* window,
+                                   ServerWindow* new_parent,
+                                   ServerWindow* old_parent) override;
+  void OnWindowVisibilityChanged(ServerWindow* window) override;
+  void OnWindowDestroyed(ServerWindow* window) override;
 
   EventDispatcherDelegate* delegate_;
   ServerWindow* root_;
 
   cc::SurfaceId surface_id_;
-  ServerWindow* capture_window_;
-
-  // Was the capture the result of clicking in the non-client area?
-  bool capture_in_nonclient_area_;
 
   using Entry = std::pair<uint32_t, EventMatcher>;
   std::map<uint32_t, EventMatcher> accelerators_;
 
+  using PointerIdToTargetMap = std::map<int32_t, PointerTarget>;
+  PointerIdToTargetMap pointer_targets_;
+
   DISALLOW_COPY_AND_ASSIGN(EventDispatcher);
 };