Port of Android platform gesture detection code to C++

ui/events/gesture_detection/scale_gesture_detector.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 "ui/events/gesture_detection/scale_gesture_detector.h"
+
+#include <limits.h>
+#include <math.h>
+
+#include "base/logging.h"
+#include "ui/events/gesture_detection/motion_event.h"
+
+using base::TimeDelta;
+using base::TimeTicks;
+
+namespace ui {
+namespace {
+
+const int kTouchStabilizeTimeMs = 128;
+
+const float kScaleFactor = .5f;
+
+}  // namespace
+
+// Note: These constants were taken directly from the default (unscaled)
+// versions found in Android's ViewConfiguration.
+ScaleGestureDetector::Config::Config()
+    : quick_scale_enabled(false),
+      min_scaling_touch_major(48),
+      min_scaling_span(200) {}
+
+ScaleGestureDetector::Config::~Config() {}
+
+bool ScaleGestureDetector::SimpleScaleGestureListener::OnScale(
+    const ScaleGestureDetector&) {
+  return false;
+}
+
+bool ScaleGestureDetector::SimpleScaleGestureListener::OnScaleBegin(
+    const ScaleGestureDetector&) {
+  return true;
+}
+
+void ScaleGestureDetector::SimpleScaleGestureListener::OnScaleEnd(
+    const ScaleGestureDetector&) {}
+
+ScaleGestureDetector::ScaleGestureDetector(const Config& config,
+                                           ScaleGestureListener* listener)
+    : listener_(listener),
+      config_(config),
+      focus_x_(0),
+      focus_y_(0),
+      quick_scale_enabled_(false),
+      curr_span_(0),
+      prev_span_(0),
+      initial_span_(0),
+      curr_span_x_(0),
+      curr_span_y_(0),
+      prev_span_x_(0),
+      prev_span_y_(0),
+      in_progress_(0),
+      span_slop_(0),
+      min_span_(0),
+      touch_upper_(0),
+      touch_lower_(0),
+      touch_history_last_accepted_(0),
+      touch_history_direction_(0),
+      touch_min_major_(0),
+      double_tap_focus_x_(0),
+      double_tap_focus_y_(0),
+      double_tap_mode_(DOUBLE_TAP_MODE_NONE),
+      event_before_or_above_starting_gesture_event_(false) {
+  DCHECK(listener_);
+  span_slop_ = config.gesture_detector_config.scaled_touch_slop * 2;
+  touch_min_major_ = config.min_scaling_touch_major;
+  min_span_ = config.min_scaling_span;
+  SetQuickScaleEnabled(config.quick_scale_enabled);
+}
+
+ScaleGestureDetector::~ScaleGestureDetector() {}
+
+bool ScaleGestureDetector::OnTouchEvent(const MotionEvent& event) {
+  curr_time_ = event.GetEventTime();
+
+  const int action = event.GetAction();
+
+  // Forward the event to check for double tap gesture.
+  if (quick_scale_enabled_) {
+    DCHECK(gesture_detector_);
+    gesture_detector_->OnTouchEvent(event);
+  }
+
+  const bool stream_complete =
+      action == MotionEvent::ACTION_UP || action == MotionEvent::ACTION_CANCEL;
+
+  if (action == MotionEvent::ACTION_DOWN || stream_complete) {
+    // Reset any scale in progress with the listener.
+    // If it's an ACTION_DOWN we're beginning a new event stream.
+    // This means the app probably didn't give us all the events. Shame on it.
+    if (in_progress_) {
+      listener_->OnScaleEnd(*this);
+      in_progress_ = false;
+      initial_span_ = 0;
+      double_tap_mode_ = DOUBLE_TAP_MODE_NONE;
+    } else if (double_tap_mode_ == DOUBLE_TAP_MODE_IN_PROGRESS &&
+               stream_complete) {
+      in_progress_ = false;
+      initial_span_ = 0;
+      double_tap_mode_ = DOUBLE_TAP_MODE_NONE;
+    }
+
+    if (stream_complete) {
+      ClearTouchHistory();
+      return true;
+    }
+  }
+
+  const bool config_changed = action == MotionEvent::ACTION_DOWN ||
+                              action == MotionEvent::ACTION_POINTER_UP ||
+                              action == MotionEvent::ACTION_POINTER_DOWN;
+
+  const bool pointer_up = action == MotionEvent::ACTION_POINTER_UP;
+  const int skip_index = pointer_up ? event.GetActionIndex() : -1;
+
+  // Determine focal point.
+  float sum_x = 0, sum_y = 0;
+  const int count = event.GetPointerCount();
+  const int div = pointer_up ? count - 1 : count;
+  float focus_x;
+  float focus_y;
+  if (double_tap_mode_ == DOUBLE_TAP_MODE_IN_PROGRESS) {
+    // In double tap mode, the focal pt is always where the double tap
+    // gesture started.
+    focus_x = double_tap_focus_x_;
+    focus_y = double_tap_focus_y_;
+    if (event.GetY() < focus_y) {
+      event_before_or_above_starting_gesture_event_ = true;
+    } else {
+      event_before_or_above_starting_gesture_event_ = false;
+    }
+  } else {
+    for (int i = 0; i < count; i++) {
+      if (skip_index == i)
+        continue;
+      sum_x += event.GetX(i);
+      sum_y += event.GetY(i);
+    }
+
+    focus_x = sum_x / div;
+    focus_y = sum_y / div;
+  }
+
+  AddTouchHistory(event);
+
+  // Determine average deviation from focal point.
+  float dev_sum_x = 0, dev_sum_y = 0;
+  for (int i = 0; i < count; i++) {
+    if (skip_index == i)
+      continue;
+
+    // Convert the resulting diameter into a radius.
+    const float touch_size = touch_history_last_accepted_ / 2;
+    dev_sum_x += std::abs(event.GetX(i) - focus_x) + touch_size;
+    dev_sum_y += std::abs(event.GetY(i) - focus_y) + touch_size;
+  }
+  const float dev_x = dev_sum_x / div;
+  const float dev_y = dev_sum_y / div;
+
+  // Span is the average distance between touch points through the focal point;
+  // i.e. the diameter of the circle with a radius of the average deviation from
+  // the focal point.
+  const float span_x = dev_x * 2;
+  const float span_y = dev_y * 2;
+  float span;
+  if (InDoubleTapMode()) {
+    span = span_y;
+  } else {
+    span = std::sqrt(span_x * span_x + span_y * span_y);
+  }
+
+  // Dispatch begin/end events as needed.
+  // If the configuration changes, notify the app to reset its current state by
+  // beginning a fresh scale event stream.
+  const bool was_in_progress = in_progress_;
+  focus_x_ = focus_x;
+  focus_y_ = focus_y;
+  if (!InDoubleTapMode() && in_progress_ &&
+      (span < min_span_ || config_changed)) {
+    listener_->OnScaleEnd(*this);
+    in_progress_ = false;
+    initial_span_ = span;
+    double_tap_mode_ = DOUBLE_TAP_MODE_NONE;
+  }
+  if (config_changed) {
+    prev_span_x_ = curr_span_x_ = span_x;
+    prev_span_y_ = curr_span_y_ = span_y;
+    initial_span_ = prev_span_ = curr_span_ = span;
+  }
+
+  const int min_span = InDoubleTapMode() ? span_slop_ : min_span_;
+  if (!in_progress_ && span >= min_span &&
+      (was_in_progress || std::abs(span - initial_span_) > span_slop_)) {
+    prev_span_x_ = curr_span_x_ = span_x;
+    prev_span_y_ = curr_span_y_ = span_y;
+    prev_span_ = curr_span_ = span;
+    prev_time_ = curr_time_;
+    in_progress_ = listener_->OnScaleBegin(*this);
+  }
+
+  // Handle motion; focal point and span/scale factor are changing.
+  if (action == MotionEvent::ACTION_MOVE) {
+    curr_span_x_ = span_x;
+    curr_span_y_ = span_y;
+    curr_span_ = span;
+
+    bool update_prev = true;
+
+    if (in_progress_) {
+      update_prev = listener_->OnScale(*this);
+    }
+
+    if (update_prev) {
+      prev_span_x_ = curr_span_x_;
+      prev_span_y_ = curr_span_y_;
+      prev_span_ = curr_span_;
+      prev_time_ = curr_time_;
+    }
+  }
+
+  return true;
+}
+
+void ScaleGestureDetector::SetQuickScaleEnabled(bool scales) {
+  quick_scale_enabled_ = scales;
+  if (quick_scale_enabled_ && !gesture_detector_) {
+    gesture_detector_.reset(
+        new GestureDetector(config_.gesture_detector_config, this, this));
+  }
+}
+
+bool ScaleGestureDetector::IsQuickScaleEnabled() const {
+  return quick_scale_enabled_;
+}
+
+bool ScaleGestureDetector::IsInProgress() const { return in_progress_; }
+
+float ScaleGestureDetector::GetFocusX() const { return focus_x_; }
+
+float ScaleGestureDetector::GetFocusY() const { return focus_y_; }
+
+float ScaleGestureDetector::GetCurrentSpan() const { return curr_span_; }
+
+float ScaleGestureDetector::GetCurrentSpanX() const { return curr_span_x_; }
+
+float ScaleGestureDetector::GetCurrentSpanY() const { return curr_span_y_; }
+
+float ScaleGestureDetector::GetPreviousSpan() const { return prev_span_; }
+
+float ScaleGestureDetector::GetPreviousSpanX() const { return prev_span_x_; }
+
+float ScaleGestureDetector::GetPreviousSpanY() const { return prev_span_y_; }
+
+float ScaleGestureDetector::GetScaleFactor() const {
+  if (InDoubleTapMode()) {
+    // Drag is moving up; the further away from the gesture start, the smaller
+    // the span should be, the closer, the larger the span, and therefore the
+    // larger the scale.
+    const bool scale_up = (event_before_or_above_starting_gesture_event_ &&
+                           (curr_span_ < prev_span_)) ||
+                          (!event_before_or_above_starting_gesture_event_ &&
+                           (curr_span_ > prev_span_));
+    const float span_diff =
+        (std::abs(1.f - (curr_span_ / prev_span_)) * kScaleFactor);
+    return prev_span_ <= 0 ? 1.f
+                           : (scale_up ? (1.f + span_diff) : (1.f - span_diff));
+  }
+  return prev_span_ > 0 ? curr_span_ / prev_span_ : 1;
+}
+
+base::TimeDelta ScaleGestureDetector::GetTimeDelta() const {
+  return curr_time_ - prev_time_;
+}
+
+base::TimeTicks ScaleGestureDetector::GetEventTime() const {
+  return curr_time_;
+}
+
+bool ScaleGestureDetector::OnDoubleTap(const MotionEvent& ev) {
+  // Double tap: start watching for a swipe.
+  double_tap_focus_x_ = ev.GetX();
+  double_tap_focus_y_ = ev.GetY();
+  double_tap_mode_ = DOUBLE_TAP_MODE_IN_PROGRESS;
+  return true;
+}
+
+void ScaleGestureDetector::AddTouchHistory(const MotionEvent& ev) {
+  const base::TimeTicks current_time = base::TimeTicks::Now();
+  const int count = ev.GetPointerCount();
+  bool accept = (current_time - touch_history_last_accepted_time_)
+                    .InMilliseconds() >= kTouchStabilizeTimeMs;
+  float total = 0;
+  int sample_count = 0;
+  for (int i = 0; i < count; i++) {
+    const bool has_last_accepted = !std::isnan(touch_history_last_accepted_);
+    const int history_size = ev.GetHistorySize();
+    const int pointersample_count = history_size + 1;
+    for (int h = 0; h < pointersample_count; h++) {
+      float major;
+      if (h < history_size) {
+        major = ev.GetHistoricalTouchMajor(i, h);
+      } else {
+        major = ev.GetTouchMajor(i);
+      }
+      if (major < touch_min_major_)
+        major = touch_min_major_;
+      total += major;
+
+      if (std::isnan(touch_upper_) || major > touch_upper_) {
+        touch_upper_ = major;
+      }
+      if (std::isnan(touch_lower_) || major < touch_lower_) {
+        touch_lower_ = major;
+      }
+
+      if (has_last_accepted) {
+        const float major_delta = major - touch_history_last_accepted_;
+        const int direction_sig =
+            major_delta > 0 ? 1 : (major_delta < 0 ? -1 : 0);
+        if (direction_sig != touch_history_direction_ ||
+            (direction_sig == 0 && touch_history_direction_ == 0)) {
+          touch_history_direction_ = direction_sig;
+          touch_history_last_accepted_time_ = h < history_size
+                                                  ? ev.GetHistoricalEventTime(h)
+                                                  : ev.GetEventTime();
+          accept = false;
+        }
+      }
+    }
+    sample_count += pointersample_count;
+  }
+
+  const float avg = total / sample_count;
+
+  if (accept) {
+    float new_accepted = (touch_upper_ + touch_lower_ + avg) / 3;
+    touch_upper_ = (touch_upper_ + new_accepted) / 2;
+    touch_lower_ = (touch_lower_ + new_accepted) / 2;
+    touch_history_last_accepted_ = new_accepted;
+    touch_history_direction_ = 0;
+    touch_history_last_accepted_time_ = ev.GetEventTime();
+  }
+}
+
+void ScaleGestureDetector::ClearTouchHistory() {
+  touch_upper_ = std::numeric_limits<float>::quiet_NaN();
+  touch_lower_ = std::numeric_limits<float>::quiet_NaN();
+  touch_history_last_accepted_ = std::numeric_limits<float>::quiet_NaN();
+  touch_history_direction_ = 0;
+  touch_history_last_accepted_time_ = base::TimeTicks();
+}
+
+bool ScaleGestureDetector::InDoubleTapMode() const {
+  return double_tap_mode_ == DOUBLE_TAP_MODE_IN_PROGRESS;
+}
+
+}  // namespace ui