Split View Mode: Support for the 2-finger bezel scroll.

athena/wm/bezel_controller.cc

+// Copyright 2014 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 "athena/wm/bezel_controller.h"
+
+#include "ui/aura/window.h"
+#include "ui/events/event_handler.h"
+
+namespace athena {
+namespace {
+
+// Using bezel swipes, the first touch that is registered is usually within
+// 5-10 pixels from the edge, but sometimes as far as 29 pixels away.
+// So setting this width fairly high for now.
+const float kBezelWidth = 20.0f;
+
+const float kScrollPositionNone = -100;
+
+bool ShouldProcessGesture(ui::EventType event_type) {
+  return event_type == ui::ET_GESTURE_SCROLL_UPDATE ||
+         event_type == ui::ET_GESTURE_SCROLL_BEGIN ||
+         event_type == ui::ET_GESTURE_BEGIN ||
+         event_type == ui::ET_GESTURE_END;
+}
+
+}  // namespace
+
+BezelController::BezelController(aura::Window* container)
+    : container_(container),
+      state_(NONE),
+      scroll_bezel_(BEZEL_NONE),
+      scroll_target_(NULL),
+      left_right_delegate_(NULL) {
+}
+
+float BezelController::GetDistance(const gfx::PointF& position,
+                                   BezelController::Bezel bezel) {
+  DCHECK(bezel == BEZEL_LEFT || bezel == BEZEL_RIGHT);
+  return bezel == BEZEL_LEFT
+             ? position.x()
+             : position.x() - container_->GetBoundsInScreen().width();
+}
+
+void BezelController::SetState(BezelController::State state,
+                               const gfx::PointF& scroll_position) {
+  if (!left_right_delegate_ || state == state_)
+    return;
+
+  if (state == BEZEL_SCROLLING_TWO_FINGERS) {
+    float delta = GetDistance(scroll_position, scroll_bezel_);
+    left_right_delegate_->ScrollBegin(scroll_bezel_, delta);
+  } else if (state_ == BEZEL_SCROLLING_TWO_FINGERS) {
+    left_right_delegate_->ScrollEnd();
+  }
+  state_ = state;
+  if (state == NONE) {
+    scroll_bezel_ = BEZEL_NONE;
+    scroll_target_ = NULL;
+  }
+}
+
+// Only implemented for LEFT and RIGHT bezels ATM.
+BezelController::Bezel BezelController::GetBezel(const gfx::PointF& location) {
+  if (location.x() < kBezelWidth) {
+    return BEZEL_LEFT;
+  } else if (location.x() >
+             container_->GetBoundsInScreen().width() - kBezelWidth) {
+    return BEZEL_RIGHT;
+  } else {
+    return BEZEL_NONE;
+  }
+}
+
+void BezelController::OnGestureEvent(ui::GestureEvent* event) {
+  // TODO (mfomitchev): Currently we aren't retargetting or consuming any of the
+  // touch events. This means that content can prevent the generation of gesture
+  // events and two-finger scroll won't work. Possible solution to this problem
+  // is hosting our own gesture recognizer or retargetting touch events at the
+  // bezel.
+
+  if (!left_right_delegate_)
+    return;
+
+  ui::EventType type = event->type();
+  if (!ShouldProcessGesture(type))
+    return;
+
+  if (scroll_target_ && event->target() != scroll_target_)
+    return;
+
+  const gfx::PointF& event_location = event->location_f();
+  const ui::GestureEventDetails& event_details = event->details();
+  int num_touch_points = event_details.touch_points();
+
+  if (type == ui::ET_GESTURE_BEGIN) {
+    if (num_touch_points > 2) {
+      SetState(IGNORE_CURRENT_SCROLL,
+               gfx::Point(kScrollPositionNone, kScrollPositionNone));
+      return;
+    }
+    BezelController::Bezel event_bezel = GetBezel(event->location_f());
+    switch (state_) {
+      case NONE:
+        scroll_bezel_ = event_bezel;
+        scroll_target_ = event->target();
+        if (event_bezel != BEZEL_LEFT && event_bezel != BEZEL_RIGHT) {
+          SetState(IGNORE_CURRENT_SCROLL,
+                   gfx::Point(kScrollPositionNone, kScrollPositionNone));
+        } else {
+          SetState(BEZEL_GESTURE_STARTED, event_location);
+        }
+        break;
+      case IGNORE_CURRENT_SCROLL:
+        break;
+      case BEZEL_GESTURE_STARTED:
+      case BEZEL_SCROLLING_ONE_FINGER:
+        DCHECK_EQ(num_touch_points, 2);
+        DCHECK(scroll_target_);
+        DCHECK_NE(scroll_bezel_, BEZEL_NONE);
+
+        if (event_bezel != scroll_bezel_) {
+          SetState(IGNORE_CURRENT_SCROLL,
+                   gfx::Point(kScrollPositionNone, kScrollPositionNone));
+          return;
+        }
+        if (state_ == BEZEL_SCROLLING_ONE_FINGER)
+          SetState(BEZEL_SCROLLING_TWO_FINGERS, event_location);
+        break;
+      case BEZEL_SCROLLING_TWO_FINGERS:
+        // Should've exited above
+        NOTREACHED();
+        break;
+    }
+  } else if (type == ui::ET_GESTURE_END) {
+    if (state_ == NONE)
+      return;
+
+    CHECK(scroll_target_);
+    if (num_touch_points == 1) {
+      SetState(NONE, gfx::Point(kScrollPositionNone, kScrollPositionNone));
+    } else {
+      SetState(IGNORE_CURRENT_SCROLL,
+               gfx::Point(kScrollPositionNone, kScrollPositionNone));
+    }
+  } else if (type == ui::ET_GESTURE_SCROLL_BEGIN) {
+    DCHECK(state_ == IGNORE_CURRENT_SCROLL || state_ == BEZEL_GESTURE_STARTED);
+    if (state_ != BEZEL_GESTURE_STARTED)
+      return;
+
+    if (num_touch_points == 1) {
+      SetState(BEZEL_SCROLLING_ONE_FINGER, event_location);
+      return;
+    }
+
+    DCHECK_EQ(num_touch_points, 2);
+    SetState(BEZEL_SCROLLING_TWO_FINGERS, event_location);
+    if (left_right_delegate_->CanScroll())
+      event->SetHandled();
+  } else if (type == ui::ET_GESTURE_SCROLL_UPDATE) {
+    if (state_ != BEZEL_SCROLLING_TWO_FINGERS)
+      return;
+
+    float scroll_delta = GetDistance(event_location, scroll_bezel_);
+    left_right_delegate_->ScrollUpdate(scroll_delta);
+    if (left_right_delegate_->CanScroll())
+      event->SetHandled();
+  }
+}
+
+}  // namespace athena