[Android] Implementation of overscroll effect for Android L

content/browser/android/edge_effect_l.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 "content/browser/android/edge_effect_l.h"
+
+#include "cc/layers/ui_resource_layer.h"
+#include "ui/base/android/system_ui_resource_manager.h"
+
+namespace content {
+
+namespace {
+
+// Time it will take the effect to fully recede in ms
+const int kRecedeTimeMs = 1000;
+
+// Time it will take before a pulled glow begins receding in ms
+const int kPullTimeMs = 167;
+
+const float kMaxAlpha = 1.f;
+
+const float kPullGlowBegin = 0.f;
+
+// Min/max velocity that will be absorbed
+const float kMinVelocity = 100.f;
+const float kMaxVelocity = 10000.f;
+
+const float kEpsilon = 0.001f;
+
+const float kSin = 0.5f;    // sin(PI / 6)
+const float kCos = 0.866f;  // cos(PI / 6);
+
+// How much dragging should effect the height of the glow image.
+// Number determined by user testing.
+const float kPullDistanceAlphaGlowFactor = 1.1f;
+
+const int kVelocityGlowFactor = 12;
+
+const ui::SystemUIResourceManager::ResourceType kResourceType =
+    ui::SystemUIResourceManager::OVERSCROLL_GLOW_L;
+
+template <typename T>
+T Lerp(T a, T b, T t) {
+  return a + (b - a) * t;
+}
+
+template <typename T>
+T Clamp(T value, T low, T high) {
+  return value < low ? low : (value > high ? high : value);
+}
+
+template <typename T>
+T Damp(T input, T factor) {
+  T result;
+  if (factor == 1) {
+    result = 1 - (1 - input) * (1 - input);
+  } else {
+    result = 1 - std::pow(1 - input, 2 * factor);
+  }
+  return result;
+}
+
+}  // namespace
+
+EdgeEffectL::EdgeEffectL(ui::SystemUIResourceManager* resource_manager)
+    : resource_manager_(resource_manager),
+      glow_(cc::UIResourceLayer::Create()),
+      glow_alpha_(0),
+      glow_scale_y_(0),
+      glow_alpha_start_(0),
+      glow_alpha_finish_(0),
+      glow_scale_y_start_(0),
+      glow_scale_y_finish_(0),
+      displacement_(0.5f),
+      target_displacement_(0.5f),
+      state_(STATE_IDLE),
+      pull_distance_(0) {
+  // Prevent the provided layers from drawing until the effect is activated.
+  glow_->SetIsDrawable(false);
+}
+
+EdgeEffectL::~EdgeEffectL() {
+  glow_->RemoveFromParent();
+}
+
+bool EdgeEffectL::IsFinished() const {
+  return state_ == STATE_IDLE;
+}
+
+void EdgeEffectL::Finish() {
+  glow_->SetIsDrawable(false);
+  pull_distance_ = 0;
+  state_ = STATE_IDLE;
+}
+
+void EdgeEffectL::Pull(base::TimeTicks current_time,
+                       float delta_distance,
+                       float displacement) {
+  target_displacement_ = displacement;
+  if (state_ == STATE_PULL_DECAY && current_time - start_time_ < duration_) {
+    return;
+  }
+  if (state_ != STATE_PULL) {
+    glow_scale_y_ = std::max(kPullGlowBegin, glow_scale_y_);
+  }
+  state_ = STATE_PULL;
+
+  start_time_ = current_time;
+  duration_ = base::TimeDelta::FromMilliseconds(kPullTimeMs);
+
+  float abs_delta_distance = std::abs(delta_distance);
+  pull_distance_ += delta_distance;
+
+  glow_alpha_ = glow_alpha_start_ = std::min(
+      kMaxAlpha,
+      glow_alpha_ + (abs_delta_distance * kPullDistanceAlphaGlowFactor));
+
+  if (pull_distance_ == 0) {
+    glow_scale_y_ = glow_scale_y_start_ = 0;
+  } else {
+    float scale = 1.f -
+                  1.f / std::sqrt(std::abs(pull_distance_) * bounds_.height()) -
+                  0.3f;
+    glow_scale_y_ = glow_scale_y_start_ = std::max(0.f, scale) / 0.7f;
+  }
+
+  glow_alpha_finish_ = glow_alpha_;
+  glow_scale_y_finish_ = glow_scale_y_;
+}
+
+void EdgeEffectL::Release(base::TimeTicks current_time) {
+  pull_distance_ = 0;
+
+  if (state_ != STATE_PULL && state_ != STATE_PULL_DECAY)
+    return;
+
+  state_ = STATE_RECEDE;
+  glow_alpha_start_ = glow_alpha_;
+  glow_scale_y_start_ = glow_scale_y_;
+
+  glow_alpha_finish_ = 0.f;
+  glow_scale_y_finish_ = 0.f;
+
+  start_time_ = current_time;
+  duration_ = base::TimeDelta::FromMilliseconds(kRecedeTimeMs);
+}
+
+void EdgeEffectL::Absorb(base::TimeTicks current_time, float velocity) {
+  state_ = STATE_ABSORB;
+
+  velocity = Clamp(std::abs(velocity), kMinVelocity, kMaxVelocity);
+
+  start_time_ = current_time;
+  // This should never be less than 1 millisecond.
+  duration_ = base::TimeDelta::FromMilliseconds(0.15f + (velocity * 0.02f));
+
+  // The glow depends more on the velocity, and therefore starts out
+  // nearly invisible.
+  glow_alpha_start_ = 0.3f;
+  glow_scale_y_start_ = std::max(glow_scale_y_, 0.f);
+
+  // Growth for the size of the glow should be quadratic to properly respond
+  // to a user's scrolling speed. The faster the scrolling speed, the more
+  // intense the effect should be for both the size and the saturation.
+  glow_scale_y_finish_ =
+      std::min(0.025f + (velocity * (velocity / 100) * 0.00015f) / 2.f, 1.f);
+  // Alpha should change for the glow as well as size.
+  glow_alpha_finish_ = Clamp(
+      glow_alpha_start_, velocity * kVelocityGlowFactor * .00001f, kMaxAlpha);
+  target_displacement_ = 0.5;
+}
+
+bool EdgeEffectL::Update(base::TimeTicks current_time) {
+  if (IsFinished())
+    return false;
+
+  const double dt = (current_time - start_time_).InMilliseconds();
+  const double t = std::min(dt / duration_.InMilliseconds(), 1.);
+  const float interp = static_cast<float>(Damp(t, 1.));
+
+  glow_alpha_ = Lerp(glow_alpha_start_, glow_alpha_finish_, interp);
+  glow_scale_y_ = Lerp(glow_scale_y_start_, glow_scale_y_finish_, interp);
+  displacement_ = (displacement_ + target_displacement_) / 2.f;
+
+  if (t >= 1.f - kEpsilon) {
+    switch (state_) {
+      case STATE_ABSORB:
+        state_ = STATE_RECEDE;
+        start_time_ = current_time;
+        duration_ = base::TimeDelta::FromMilliseconds(kRecedeTimeMs);
+
+        glow_alpha_start_ = glow_alpha_;
+        glow_scale_y_start_ = glow_scale_y_;
+
+        glow_alpha_finish_ = 0.f;
+        glow_scale_y_finish_ = 0.f;
+        break;
+      case STATE_PULL:
+        // Hold in this state until explicitly released.
+        break;
+      case STATE_PULL_DECAY:
+        state_ = STATE_RECEDE;
+        break;
+      case STATE_RECEDE:
+        Finish();
+        break;
+      default:
+        break;
+    }
+  }
+
+  bool one_last_frame = false;
+  if (state_ == STATE_RECEDE && glow_scale_y_ <= 0) {
+    Finish();
+    one_last_frame = true;
+  }
+
+  return !IsFinished() || one_last_frame;
+}
+
+void EdgeEffectL::ApplyToLayers(const gfx::SizeF& size,
+                                const gfx::Transform& transform) {
+  if (IsFinished())
+    return;
+
+  // An empty window size, while meaningless, is also relatively harmless, and
+  // will simply prevent any drawing of the layers.
+  if (size.IsEmpty()) {
+    glow_->SetIsDrawable(false);
+    return;
+  }
+
+  const float r = size.width() * 0.75f / kSin;
+  const float y = kCos * r;
+  const float h = r - y;
+  bounds_ = gfx::Size(size.width(), (int)std::min(size.height(), h));
+  gfx::Size image_bounds(r, std::min(1.f, glow_scale_y_) * bounds_.height());
+
+  glow_->SetIsDrawable(true);
+  glow_->SetUIResourceId(resource_manager_->GetUIResourceId(kResourceType));
+  glow_->SetTransformOrigin(gfx::Point3F(bounds_.width() * 0.5f, 0, 0));
+  glow_->SetBounds(image_bounds);
+  glow_->SetContentsOpaque(false);
+  glow_->SetOpacity(Clamp(glow_alpha_, 0.f, 1.f));
+
+  const float displacement = Clamp(displacement_, 0.f, 1.f) - 0.5f;
+  const float displacement_offset_x = bounds_.width() * displacement * 0.5f;
+  const float image_offset_x = (bounds_.width() - image_bounds.width()) * 0.5f;
+  gfx::Transform offset_transform;
+  offset_transform.Translate(image_offset_x - displacement_offset_x, 0);
+  offset_transform.ConcatTransform(transform);
+  glow_->SetTransform(offset_transform);
+}
+
+void EdgeEffectL::SetParent(cc::Layer* parent) {
+  if (glow_->parent() != parent)
+    parent->AddChild(glow_);
+  glow_->SetUIResourceId(resource_manager_->GetUIResourceId(kResourceType));
+}
+
+// static
+void EdgeEffectL::PreloadResources(
+    ui::SystemUIResourceManager* resource_manager) {
+  DCHECK(resource_manager);
+  resource_manager->PreloadResource(kResourceType);
+}
+
+}  // namespace content