Toggle spoken feedback if two fingers are held down.

ui/chromeos/touch_accessibility_enabler.cc

+// Copyright 2016 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 "ui/chromeos/touch_accessibility_enabler.h"
+
+#include <utility>
+
+#include "base/logging.h"
+#include "base/time/default_tick_clock.h"
+#include "ui/aura/window.h"
+#include "ui/aura/window_event_dispatcher.h"
+#include "ui/aura/window_tree_host.h"
+#include "ui/events/event.h"
+#include "ui/events/event_processor.h"
+#include "ui/events/event_utils.h"
+
+namespace ui {
+
+namespace {
+
+// Delay between timer callbacks. Each one plays a tick sound.
+const int kTimerDelayInMS = 500;

[oshima, 2016/11/08 18:14:43]

nit: constexpr

[dmazzoni, 2016/11/08 20:43:47]

Done.

+
+// The number of ticks of the timer before toggling spoken feedback.
+const int kTimerTicksToToggleSpokenFeedback = 7;
+
+}  // namespace
+
+TouchAccessibilityEnabler::TouchAccessibilityEnabler(
+    aura::Window* root_window,
+    TouchAccessibilityEnablerDelegate* delegate)
+    : root_window_(root_window),
+      delegate_(delegate),
+      state_(NO_FINGERS_DOWN),
+      tick_clock_(NULL) {
+  DCHECK(root_window);

[oshima, 2016/11/08 18:14:43]

delegate too?

[dmazzoni, 2016/11/08 20:43:47]

Done.

+  root_window->GetHost()->GetEventSource()->AddEventRewriter(this);
+}
+
+TouchAccessibilityEnabler::~TouchAccessibilityEnabler() {
+  root_window_->GetHost()->GetEventSource()->RemoveEventRewriter(this);
+}
+
+ui::EventRewriteStatus TouchAccessibilityEnabler::RewriteEvent(
+    const ui::Event& event,
+    std::unique_ptr<ui::Event>* rewritten_event) {

[oshima, 2016/11/08 18:14:43]

so eventhandler doesn't work?

[dmazzoni, 2016/11/08 20:43:47]

Oh, good catch! Originally I did rewrite an event but I didn't
need to after all. Switched to EventHandler using AddPreTargetHandler
and confirmed that it works.

[dmazzoni, 2016/11/08 21:18:04]

Actually after testing some more, it doesn't work as an EventHandler.
It works for toggling it on, but toggling spoken feedback on installs
a different EventRewriter for touch accessibility, and that rewrites
all of the events before any EventHandlers get them - so we can't
toggle off.

I think it's simpler to just make this an EventRewriter. I added
a comment explaining why.

[sadrul, 2016/11/10 20:39:03]

I would like to understand more, because this is a misuse of the rewriter API.

What is the event-rewriter that gets installed with spoken feedback? Can that
notify this handler before it does the rewrite?

+  if (!event.IsTouchEvent())
+    return ui::EVENT_REWRITE_CONTINUE;
+
+  const ui::TouchEvent& touch_event = static_cast<const ui::TouchEvent&>(event);
+  HandleTouchEvent(touch_event);
+  return ui::EVENT_REWRITE_CONTINUE;
+}
+
+ui::EventRewriteStatus TouchAccessibilityEnabler::NextDispatchEvent(
+    const ui::Event& last_event,
+    std::unique_ptr<ui::Event>* new_event) {
+  NOTREACHED();
+  return ui::EVENT_REWRITE_CONTINUE;
+}
+
+void TouchAccessibilityEnabler::HandleTouchEvent(const ui::TouchEvent& event) {
+  const ui::EventType type = event.type();
+  const gfx::PointF& location = event.location_f();
+  const int touch_id = event.touch_id();
+
+  if (type == ui::ET_TOUCH_PRESSED) {
+    touch_ids_.push_back(touch_id);
+    touch_locations_.insert(std::pair<int, gfx::PointF>(touch_id, location));
+  } else if (type == ui::ET_TOUCH_RELEASED || type == ui::ET_TOUCH_CANCELLED) {
+    auto iter = std::find(touch_ids_.begin(), touch_ids_.end(), touch_id);
+
+    // Can happen if this object is constructed while fingers were down.
+    if (iter == touch_ids_.end())
+      return;
+
+    touch_ids_.erase(iter);
+    touch_locations_.erase(touch_id);
+  } else if (type == ui::ET_TOUCH_MOVED) {
+    auto iter = std::find(touch_ids_.begin(), touch_ids_.end(), touch_id);
+
+    // Can happen if this object is constructed while fingers were down.
+    if (iter == touch_ids_.end())
+      return;
+
+    float delta = (location - touch_locations_[*iter]).Length();
+    if (delta > gesture_detector_config_.double_tap_slop) {
+      state_ = WAIT_FOR_NO_FINGERS;
+      CancelTimer();
+      return;
+    }
+  } else {
+    NOTREACHED() << "Unexpected event type received: " << event.name();
+    return;
+  }
+
+  if (touch_ids_.size() == 0) {
+    state_ = NO_FINGERS_DOWN;
+    CancelTimer();
+    return;
+  }
+
+  if (touch_ids_.size() > 2) {
+    state_ = WAIT_FOR_NO_FINGERS;
+    CancelTimer();
+    return;
+  }
+
+  if (state_ == NO_FINGERS_DOWN && event.type() == ui::ET_TOUCH_PRESSED) {
+    state_ = ONE_FINGER_DOWN;
+  } else if (state_ == ONE_FINGER_DOWN &&
+             event.type() == ui::ET_TOUCH_PRESSED) {
+    state_ = TWO_FINGERS_DOWN;
+    two_finger_start_time_ = Now();
+    StartTimer();
+  }
+}
+
+base::TimeTicks TouchAccessibilityEnabler::Now() {
+  if (tick_clock_) {
+    // This is the same as what EventTimeForNow() does, but here we do it
+    // with a clock that can be replaced with a simulated clock for tests.
+    return tick_clock_->NowTicks();
+  }
+  return ui::EventTimeForNow();
+}
+
+void TouchAccessibilityEnabler::StartTimer() {
+  if (timer_.IsRunning())
+    return;
+
+  timer_.Start(FROM_HERE, base::TimeDelta::FromMilliseconds(kTimerDelayInMS),
+               this, &ui::TouchAccessibilityEnabler::OnTimer);
+}
+
+void TouchAccessibilityEnabler::CancelTimer() {
+  if (timer_.IsRunning())
+    timer_.Stop();
+}
+
+void TouchAccessibilityEnabler::OnTimer() {
+  base::TimeTicks now = Now();
+  double tick_count_f =
+      (now - two_finger_start_time_).InMillisecondsF() / kTimerDelayInMS;
+  int tick_count = roundf(tick_count_f);
+  if (tick_count >= 1 && tick_count < kTimerTicksToToggleSpokenFeedback) {
+    delegate_->PlaySpokenFeedbackToggleCountdown(tick_count);
+  }
+  if (tick_count == kTimerTicksToToggleSpokenFeedback) {
+    delegate_->ToggleSpokenFeedback();
+    state_ = WAIT_FOR_NO_FINGERS;
+  }
+}
+
+}  // namespace ui