Scaling scroll/fling events in multi-monitor setup

ash/display/event_transformation_handler.cc

+// 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.
+
+#include "ash/display/event_transformation_handler.h"
+
+#include "ash/display/display_manager.h"
+#include "ash/screen_ash.h"
+#include "ash/shell.h"
+#include "ash/wm/coordinate_conversion.h"
+#include "ash/wm/window_util.h"
+#include "ui/aura/root_window.h"
+#include "ui/aura/window.h"
+#include "ui/base/events/event.h"
+#include "ui/compositor/dip_util.h"
+#include "ui/gfx/display.h"
+#include "ui/gfx/screen.h"
+
+namespace ash {
+namespace internal {
+namespace {
+
+// Boost factor for non-integrated displays.
+const float kBoostForNonIntegrated = 1.20f;
+}
+
+EventTransformationHandler::EventTransformationHandler()
+    : transformation_mode_(TRANSFORM_AUTO) {
+}
+
+EventTransformationHandler::~EventTransformationHandler() {
+}
+
+void EventTransformationHandler::OnScrollEvent(ui::ScrollEvent* event) {
+  if (transformation_mode_ == TRANSFORM_NONE)
+    return;
+
+  // Get the device scale factor and stack it on the final scale factor.
+  gfx::Point point_in_screen(event->location());
+  aura::Window* target = static_cast<aura::Window*>(event->target());
+  const float scale_at_target = ui::GetDeviceScaleFactor(target->layer());
+  float scale = scale_at_target;
+
+  // Apply some additional scaling if the display is non-integrated.
+  wm::ConvertPointToScreen(target, &point_in_screen);
+  const gfx::Display& display =
+      Shell::GetScreen()->GetDisplayNearestPoint(point_in_screen);
+  DisplayManager* display_manager = Shell::GetInstance()->display_manager();
+  if (!display_manager->IsInternalDisplayId(display.id()))
+    scale *= kBoostForNonIntegrated;
+
+  event->Scale(scale);
+}
+
+}  // namespace internal
+}  // namespace ash
+