Scaling scroll/fling events in multi-monitor setup

ash/display/event_transformation_handler.h

+// Copyright (c) 2013 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 ASH_DISPLAY_EVENT_TRANSFORMATION_HANDLER_H_
+#define ASH_DISPLAY_EVENT_TRANSFORMATION_HANDLER_H_
+
+#include "ash/ash_export.h"
+#include "base/compiler_specific.h"
+#include "ui/base/events/event_handler.h"
+
+namespace ash {
+
+namespace internal {
+
+// An event filter that transforms input event properties in extended desktop
+// environment. It currently handles only ScrollEvents.
+class ASH_EXPORT EventTransformationHandler : public ui::EventHandler {
+ public:
+  enum TransformationMode {
+    TRANSFORM_AUTO,   // Transform events by the default amount.
+                      // 1. Linear scaling w.r.t. the device scale factor.
+                      // 2. Add 20% more for non-integrated displays.
+    TRANSFORM_NONE,   // No transformation.
+  };
+
+  EventTransformationHandler();
+  virtual ~EventTransformationHandler();
+
+  void set_transformation_mode(TransformationMode transformation_mode) {
+    transformation_mode_ = transformation_mode;
+  }
+
+  // Overridden from ui::EventHandler.
+  virtual void OnScrollEvent(ui::ScrollEvent* event) OVERRIDE;
+
+ private:
+  TransformationMode transformation_mode_;
+
+  DISALLOW_COPY_AND_ASSIGN(EventTransformationHandler);
+};
+
+}  // namespace internal
+}  // namespace ash
+
+#endif  // ASH_DISPLAY_EVENT_TRANSFORMATION_HANDLER_H_
+