Improve scroll performance on Windows 10 with high precision touchpads.

ui/gfx/win/direct_manipulation.h

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef UI_GFX_WIN_DIRECT_MANIPULATION_H_
+#define UI_GFX_WIN_DIRECT_MANIPULATION_H_
+
+#include <directmanipulation.h>
+
+#include "base/win/scoped_comptr.h"
+#include "ui/gfx/geometry/rect.h"
+#include "ui/gfx/gfx_export.h"
+
+namespace gfx {
+namespace win {
+
+// Windows 10 provides a new API called Direct Manipulation which generates
+// smooth scroll events via WM_MOUSEWHEEL messages with predictable deltas
+// on high precision touch pads. This basically requires the application window
+// to register as a Direct Manipulation consumer. The way mouse wheel messages
+// are dispatched is
+// 1. The foreground window is checked to see if it is a Direct Manipulation
+//    consumer.
+// 2. If it is then Direct Manipulation takes over and sends the following
+//    messages. WM_POINTERACTIVATE, WM_POINTERDOWN and DM_POINTERHITTEST.
+// 3. It then posts WM_MOUSEWHEEL messages with precision deltas which vary
+//    based on the amount of the scroll.
+// 4. If the foreground window is not a Direct Manipulation consumer, it
+//    then takes a fallback route where it posts WM_MOUSEWHEEL messages
+//    with precision but varying deltas to the window. There is a also
+//    a slight delay in receiving the first set of mouse wheel messages.
+//    This causes scrolling to appear janky and jumpy.
+// Our approach for addressing this is to do the absolute minimum to
+// register our window as a Direct Manipulation consumer. This class
+// provides the necessary functionality to register the passed in HWND as a
+// Direct Manipulation consumer. We don't rely on Direct manipulation
+// to do the smooth scrolling in the background thread as documented on
+// msdn.
+class GFX_EXPORT DirectManipulationHelper {
+ public:
+  // Creates an instance of this class if Direct Manipulation is enabled on
+  // the platform. If not returns NULL.
+  static DirectManipulationHelper* CreateInstance();

[sky, 2015/08/11 23:45:02]

Make this return a scoped_ptr.

[ananta, 2015/08/12 00:41:58]

Done.

+
+  // This function instantiates Direct Manipulation and creates a viewport for
+  // the passed in |window|.
+  // consumer. Most of the code is boiler plate and is based on the sample.
+  void Initialize(HWND window);
+
+  // Sets the bounds of the fake Direct manipulation viewport to match those
+  // of the legacy window.
+  void SetBounds(const gfx::Rect& bounds);
+
+  // Registers the passed in |window| as a Direct Manipulation consumer.
+  void Activate(HWND window);
+
+  // Passes the WM_MOUSEWHEEL messages to Direct Manipulation. This is for
+  // logistics purposes.
+  void HandleMouseWheel(HWND window, UINT message, WPARAM w_param,
+      LPARAM l_param);
+
+ private:
+  DirectManipulationHelper() {}

[sky, 2015/08/11 23:45:02]

Don't inline this.

[ananta, 2015/08/12 00:41:58]

Done.

+
+  base::win::ScopedComPtr<IDirectManipulationManager2> manager_;
+  base::win::ScopedComPtr<IDirectManipulationCompositor> compositor_;
+  base::win::ScopedComPtr<IDirectManipulationUpdateManager> update_manager_;
+  base::win::ScopedComPtr<IDirectManipulationFrameInfoProvider> frame_info_;
+  base::win::ScopedComPtr<IDirectManipulationViewport2> view_port_outer_;
+
+  DISALLOW_COPY_AND_ASSIGN(DirectManipulationHelper);
+};
+
+}  // namespace win
+}  // namespace gfx
+
+#endif  // UI_GFX_WIN_DIRECT_WRITE_H_