Screen Magnifier: Change the zoom level with Alt + Scroll

ash/magnifier/magnification_controller.cc

 // Copyright (c) 2012 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/magnifier/magnification_controller.h"
 
 #include "ash/shell.h"
 #include "ui/aura/event.h"
 #include "ui/aura/event_filter.h"
 #include "ui/aura/root_window.h"
 #include "ui/aura/shared/compound_event_filter.h"
 #include "ui/aura/window.h"
 #include "ui/aura/window_property.h"
 #include "ui/gfx/point3.h"
 #include "ui/gfx/screen.h"
 #include "ui/compositor/dip_util.h"
 #include "ui/compositor/layer.h"
 #include "ui/compositor/layer_animation_observer.h"
 #include "ui/compositor/scoped_layer_animation_settings.h"
 
 namespace {
 
 const float kMaxMagnifiedScale = 4.0f;
 const float kMaxMagnifiedScaleThreshold = 4.0f;
 const float kMinMagnifiedScaleThreshold = 1.1f;
 const float kNonMagnifiedScale = 1.0f;
 
 const float kInitialMagnifiedScale = 2.0f;
+const float kScrollScaleChangeFactor = 0.05f;
 
 }  // namespace
 
 namespace ash {
 namespace internal {
 
 ////////////////////////////////////////////////////////////////////////////////
 // MagnificationControllerImpl:
 
 class MagnificationControllerImpl : virtual public MagnificationController,
@@ skipping 375 matching lines @@
 ////////////////////////////////////////////////////////////////////////////////
 // MagnificationControllerImpl: aura::EventFilter implementation
 
 bool MagnificationControllerImpl::PreHandleKeyEvent(aura::Window* target,
                                                     aura::KeyEvent* event) {
   return false;
 }
 
 bool MagnificationControllerImpl::PreHandleMouseEvent(aura::Window* target,
                                                       aura::MouseEvent* event) {
+  if (event->type() == ui::ET_SCROLL && event->IsAltDown()) {
+    aura::ScrollEvent* scroll_event = static_cast<aura::ScrollEvent*>(event);
+    float scale = GetScale();
+    scale += scroll_event->y_offset() * kScrollScaleChangeFactor;
+    SetScale(scale, true);
+    return true;
+  }
+
   if (IsMagnified() && event->type() == ui::ET_MOUSE_MOVED) {
     aura::RootWindow* current_root = target->GetRootWindow();
     gfx::Rect root_bounds = current_root->bounds();
 
     if (root_bounds.Contains(event->root_location())) {
       if (current_root != root_window_)
         SwitchTargetRootWindow(current_root);
 
       OnMouseMove(event->root_location());
     }
@@ skipping 17 matching lines @@
 ////////////////////////////////////////////////////////////////////////////////
 // MagnificationController:
 
 // static
 MagnificationController* MagnificationController::CreateInstance() {
   return new MagnificationControllerImpl();
 }
 
 }  // namespace internal
 }  // namespace ash