Initial patch set to implement improved touch support for screen magnification

ash/magnifier/magnification_controller.cc

Index: ash/magnifier/magnification_controller.cc
diff --git a/ash/magnifier/magnification_controller.cc b/ash/magnifier/magnification_controller.cc
index c677caae5c56b2b741f3a8ae9c87dffc785470b0..bcd763e0c710ba0830bbd346680007bb316c16cd 100644
--- a/ash/magnifier/magnification_controller.cc
+++ b/ash/magnifier/magnification_controller.cc
@@ -20,6 +20,7 @@
 #include "base/command_line.h"
 #include "base/synchronization/waitable_event.h"
 #include "base/timer/timer.h"
+#include "chromeos/chromeos_switches.h"
 #include "ui/aura/client/cursor_client.h"
 #include "ui/aura/window.h"
 #include "ui/aura/window_tree_host.h"
@@ -34,6 +35,7 @@
 #include "ui/display/screen.h"
 #include "ui/events/event.h"
 #include "ui/events/event_handler.h"
+#include "ui/events/gesture_event_details.h"
 #include "ui/gfx/geometry/point3_f.h"
 #include "ui/gfx/geometry/point_conversions.h"
 #include "ui/gfx/geometry/point_f.h"
@@ -191,6 +193,7 @@ class MagnificationControllerImpl : public MagnificationController,
   void OnMouseEvent(ui::MouseEvent* event) override;
   void OnScrollEvent(ui::ScrollEvent* event) override;
   void OnTouchEvent(ui::TouchEvent* event) override;
+  void OnGestureEvent(ui::GestureEvent* event) override;
 
   // Moves the view port when |point| is located within
   // |x_panning_margin| and |y_pannin_margin| to the edge of the visible
@@ -261,6 +264,9 @@ class MagnificationControllerImpl : public MagnificationController,
   // mode.
   bool disable_move_magnifier_delay_;
 
+  // Flag whether user is currently performing pinch gesture or not.
+  bool is_performing_pinch_gesture_;
+
   DISALLOW_COPY_AND_ASSIGN(MagnificationControllerImpl);
 };
 
@@ -275,7 +281,8 @@ MagnificationControllerImpl::MagnificationControllerImpl()
       move_cursor_after_animation_(false),
       scale_(kNonMagnifiedScale),
       scroll_direction_(SCROLL_NONE),
-      disable_move_magnifier_delay_(false) {
+      disable_move_magnifier_delay_(false),
+      is_performing_pinch_gesture_(false) {
   Shell::GetInstance()->AddPreTargetHandler(this);
   root_window_->AddObserver(this);
   point_of_interest_ = root_window_->bounds().CenterPoint();
@@ -690,6 +697,45 @@ void MagnificationControllerImpl::OnTouchEvent(ui::TouchEvent* event) {
   }
 }
 
+void MagnificationControllerImpl::OnGestureEvent(ui::GestureEvent* event) {
+  if (!base::CommandLine::ForCurrentProcess()->HasSwitch(
+          chromeos::switches::kEnableTouchSupportForScreenMagnification)) {
+    return;
+  }
+
+  const ui::GestureEventDetails& details = event->details();
+  if (details.type() == ui::ET_GESTURE_SCROLL_UPDATE &&
+      details.touch_points() == 2 && !is_performing_pinch_gesture_) {
+    gfx::Rect viewport_rect_in_dip = GetViewportRect();
+    viewport_rect_in_dip.Offset(details.scroll_x() * -1,
+                                details.scroll_y() * -1);
+    const gfx::Rect& viewport_rect_in_pixel =
+        ui::ConvertRectToPixel(root_window_->layer(), viewport_rect_in_dip);
+    MoveWindow(viewport_rect_in_pixel.origin(), false);
+    event->SetHandled();
+  } else if (details.type() == ui::ET_GESTURE_PINCH_BEGIN) {
+    // Set this flag to prevent scrolling while user is changing zoom level.
+    is_performing_pinch_gesture_ = true;
+    event->SetHandled();
+  } else if (details.type() == ui::ET_GESTURE_PINCH_END) {
+    is_performing_pinch_gesture_ = false;
+    event->SetHandled();
+  } else if (details.type() == ui::ET_GESTURE_PINCH_UPDATE &&
+             details.touch_points() == 3) {
+    float scale = GetScale() * details.scale();
+
+    if (scale < kMinMagnifiedScaleThreshold) {
+      scale = kMinMagnifiedScaleThreshold;
+    } else if (scale > kMaxMagnifiedScaleThreshold) {
+      scale = kMaxMagnifiedScaleThreshold;
+    }
+
+    point_of_interest_ = event->root_location();

[yoshiki, 2017/01/20 05:26:33]

Should we move the mouse cursor to the point of interest here (or in
GESTURE_PINCH_END handler)? Otherwise the magnification window may jump suddenly
from here to the mouse cursor position just after user moves mouse, I think.

[yawano, 2017/02/06 06:49:04]

I don't think we need to do it. IIUC, the mouse cursor is managed in the actual
(physical) screen coordinate, i.e. the cursor will stick to the current physical
location on the screen even if we change zoom level or scroll.

[yoshiki, 2017/02/06 17:22:07]

Thank you for explanation. Then, ok.

+    SetScale(scale, false);
+    event->SetHandled();
+  }
+}
+
 void MagnificationControllerImpl::MoveMagnifierWindowFollowPoint(
     const gfx::Point& point,
     int x_panning_margin,