Port of Android platform gesture detection code to C++

ui/events/gesture_detection/velocity_tracker_state.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/velocity_tracker_state.h"
+
+#include "base/logging.h"
+
+namespace ui {
+namespace {
+// Special constant to request the velocity of the active pointer.
+const int ACTIVE_POINTER_ID = -1;
+}
+
+VelocityTrackerState::VelocityTrackerState()
+    : velocity_tracker_(VelocityTracker::STRATEGY_DEFAULT),
+      active_pointer_id_(ACTIVE_POINTER_ID) {}
+
+VelocityTrackerState::VelocityTrackerState(VelocityTracker::Strategy strategy)
+    : velocity_tracker_(strategy), active_pointer_id_(ACTIVE_POINTER_ID) {}
+
+VelocityTrackerState::~VelocityTrackerState() {}
+
+void VelocityTrackerState::Clear() {
+  velocity_tracker_.Clear();
+  active_pointer_id_ = ACTIVE_POINTER_ID;
+  calculated_id_bits_.clear();
+}
+
+void VelocityTrackerState::AddMovement(const MotionEvent& event) {
+  velocity_tracker_.AddMovement(event);
+}
+
+void VelocityTrackerState::ComputeCurrentVelocity(int32_t units,
+                                                  float max_velocity) {
+  DCHECK_GE(max_velocity, 0);
+
+  BitSet32 id_bits(velocity_tracker_.GetCurrentPointerIdBits());
+  calculated_id_bits_ = id_bits;
+
+  for (uint32_t index = 0; !id_bits.is_empty(); index++) {
+    uint32_t id = id_bits.clear_first_marked_bit();
+
+    float vx, vy;
+    velocity_tracker_.GetVelocity(id, &vx, &vy);
+
+    vx = vx * units / 1000.f;
+    vy = vy * units / 1000.f;
+
+    if (vx > max_velocity)
+      vx = max_velocity;
+    else if (vx < -max_velocity)
+      vx = -max_velocity;
+
+    if (vy > max_velocity)
+      vy = max_velocity;
+    else if (vy < -max_velocity)
+      vy = -max_velocity;
+
+    Velocity& velocity = calculated_velocity_[index];
+    velocity.vx = vx;
+    velocity.vy = vy;
+  }
+}
+
+float VelocityTrackerState::GetXVelocity(int32_t id) const {
+  float vx;
+  GetVelocity(id, &vx, NULL);
+  return vx;
+}
+
+float VelocityTrackerState::GetYVelocity(int32_t id) const {
+  float vy;
+  GetVelocity(id, NULL, &vy);
+  return vy;
+}
+
+void VelocityTrackerState::GetVelocity(int32_t id,
+                                       float* out_vx,
+                                       float* out_vy) const {
+  DCHECK(out_vx || out_vy);
+  if (id == ACTIVE_POINTER_ID)
+    id = velocity_tracker_.GetActivePointerId();
+
+  float vx, vy;
+  if (id >= 0 && id <= VelocityTracker::MAX_POINTER_ID &&
+      calculated_id_bits_.has_bit(id)) {
+    uint32_t index = calculated_id_bits_.get_index_of_bit(id);
+    const Velocity& velocity = calculated_velocity_[index];
+    vx = velocity.vx;
+    vy = velocity.vy;
+  } else {
+    vx = 0;
+    vy = 0;
+  }
+
+  if (out_vx)
+    *out_vx = vx;
+
+  if (out_vy)
+    *out_vy = vy;
+}
+
+}  // namespace ui