Implement initial version of scroll end effect

chrome/browser/ui/views/frame/scroll_end_effect_controller_ash.cc

 // Copyright 2013 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 "chrome/browser/ui/views/frame/scroll_end_effect_controller_ash.h"
 
-ScrollEndEffectController* ScrollEndEffectController::Create() {
-  return new ScrollEndEffectControllerAsh();
+#include "chrome/browser/ui/views/frame/browser_frame.h"
+#include "chrome/browser/ui/views/frame/browser_view.h"
+#include "content/public/browser/web_contents.h"
+#include "content/public/browser/web_contents_view.h"
+#include "ui/aura/window.h"
+#include "ui/compositor/layer_type.h"
+#include "ui/gfx/rect.h"
+#include "ui/gfx/transform.h"
+
+namespace {
+// This factor is used to control how much translation is applied relative to
+// the size of the window. Specifically translation is limited to a max of
+// window_size * factor.
+const float kScrollEndEffectFactor = 0.10;
 }
 
-ScrollEndEffectControllerAsh::ScrollEndEffectControllerAsh() {
+ScrollEndEffectController* ScrollEndEffectController::Create(
+    BrowserView* view) {
+  return new ScrollEndEffectControllerAsh(view);
+}
+
+ScrollEndEffectControllerAsh::ScrollEndEffectControllerAsh(BrowserView* view)
+    : browser_view_(view),
+      is_effect_active_(false),
+      browser_frame_layer_(NULL),
+      web_contents_layer_(NULL),
+      non_client_layer_(NULL),
+      web_contents_parent_(NULL),
+      non_client_view_(NULL) {
 }
 
 ScrollEndEffectControllerAsh::~ScrollEndEffectControllerAsh() {
 }
 
 void ScrollEndEffectControllerAsh::OverscrollUpdate(int delta_y) {
-  // TODO(rharrison): Implement initial version of scroll end effect
+  if (browser_view_ == NULL || browser_view_->frame() == NULL) {
+    return;
+  }
+
+  if (delta_y == 0 && is_effect_active_) {
+    if (browser_frame_layer_) {
+      ApplyDelta(browser_frame_layer_, browser_frame_layer_->bounds(), 0);
+      DeactivateEffect();
+    }
+    return;
+  }
+
+  if (!is_effect_active_)
+    ActivateEffect();
+
+  int capped_delta_y = delta_y;
+  gfx::Rect bounds = browser_frame_layer_->bounds();
+  // Limiting the delta size being a proportion of the frame bounds size.
+  if (capped_delta_y > 0) {
+    capped_delta_y = std::min(static_cast<int>(roundf(bounds.height() *
+                                                      kScrollEndEffectFactor)),
+                              capped_delta_y);
+  } else if (capped_delta_y < 0) {
+    capped_delta_y = -std::min(static_cast<int>(roundf(bounds.height() *
+                                                       kScrollEndEffectFactor)),
+                               -capped_delta_y);
+  }
+  ApplyDelta(browser_frame_layer_, bounds, capped_delta_y);
 }
+
+void ScrollEndEffectControllerAsh::ActivateEffect() {
+  is_effect_active_ = true;
+
+  // Get layers for all of the parts to be manipulated
+  browser_frame_layer_ = browser_view_->frame()->GetLayer();
+  web_contents_layer_ = browser_view_-> GetActiveWebContents()->GetView()->
+      GetNativeView()->layer();
+  non_client_view_ = browser_view_->frame()->GetContentsView();
+  non_client_view_->SetPaintToLayer(true);
+  non_client_layer_ = non_client_view_->layer();
+  non_client_layer_->SetFillsBoundsOpaquely(false);
+  //  non_client_layer_->SetOpacity(0.5);
+
+  CHECK(web_contents_layer_ != NULL);

[sadrul, 2013/08/20 16:14:59]

CHECK(web_contents_layer_), or CHECK_NE

[rharrison, 2013/08/20 19:57:41]

Done.

+  CHECK(non_client_layer_ != NULL);
+
+  // Setup clipping layers
+  frame_clipping_layer_.reset(new ui::Layer(ui::LAYER_NOT_DRAWN));
+  frame_clipping_layer_->set_name("OverscrollFrameClippingLayer");
+  frame_clipping_layer_->SetMasksToBounds(true);
+  gfx::Rect frame_clipping_bounds = browser_frame_layer_->bounds();
+  frame_clipping_bounds.set_origin(gfx::Point(0,0));

[sadrul, 2013/08/20 16:14:59]

gfx::Point()

[rharrison, 2013/08/20 19:57:41]

Done.

+  frame_clipping_layer_->SetBounds(frame_clipping_bounds);
+
+  web_clipping_layer_.reset(new ui::Layer(ui::LAYER_NOT_DRAWN));
+  web_clipping_layer_->set_name("OverscrollWebClippingLayer");
+  web_clipping_layer_->SetMasksToBounds(true);
+  gfx::Rect web_clipping_bounds = browser_frame_layer_->bounds();
+  non_content_height_ = browser_frame_layer_->bounds().height() -
+      web_contents_layer_->bounds().height();
+  web_clipping_bounds.set_height(browser_frame_layer_->bounds().height() -
+                                 non_content_height_);
+  web_clipping_bounds.set_origin(gfx::Point(0, non_content_height_));
+  web_clipping_layer_->SetBounds(web_clipping_bounds);
+
+  // Move the web contents since bounds are relative to the parent layer
+  gfx::Rect web_contents_bounds = web_clipping_bounds;
+  web_contents_parent_ = web_contents_layer_->parent();
+  web_contents_bounds.set_origin(gfx::Point(0, 0));
+  web_contents_bounds_ = web_contents_layer_->bounds();
+  web_contents_layer_->SetBounds(web_contents_bounds);
+
+  // Adjust the toplogy of the layer tree to add clipping layers
+  browser_frame_layer_->Add(frame_clipping_layer_.get());
+  frame_clipping_layer_->Add(non_client_layer_);
+  frame_clipping_layer_->Add(web_clipping_layer_.get());
+  web_clipping_layer_->Add(web_contents_layer_);

[sadrul, 2013/08/20 16:14:59]

I think this looks reasonable. Two notes:
 * Is it necessary to maintain the pointers to the layers? (i.e. instead of
keeping |browser_frame_layer_| around, why not use
|browser_view_->frame()->GetLayer()| in a local variable where necessary? etc.

 * Can you please explain the layer hierarchy before/during/after the
overscroll?

[rharrison, 2013/08/20 19:57:41]

Done.

+}
+
+void ScrollEndEffectControllerAsh::DeactivateEffect() {
+  is_effect_active_ = false;
+
+  web_contents_layer_->SetBounds(web_contents_bounds_);
+  web_contents_parent_->Add(web_contents_layer_);
+  web_contents_parent_ = NULL;
+  web_contents_layer_ = NULL;
+
+  frame_clipping_layer_->Remove(non_client_layer_);
+  non_client_view_->SetPaintToLayer(false);
+  non_client_layer_ = NULL;
+  non_client_view_ = NULL;
+
+  frame_clipping_layer_->Remove(web_clipping_layer_.get());
+  web_clipping_layer_.reset();
+  browser_frame_layer_->Remove(frame_clipping_layer_.get());
+  frame_clipping_layer_.reset();
+  browser_frame_layer_ = NULL;
+}
+
+void ScrollEndEffectControllerAsh::ApplyDelta(ui::Layer* frame,
+                                              gfx::Rect bounds,
+                                              int delta_y) {
+  float scale_factor = std::abs(delta_y);
+  scale_factor /= bounds.height();
+  scale_factor = 1 - scale_factor;
+
+  gfx::Transform frame_transform;
+  if (delta_y > 0) {
+    frame_transform.Translate(0, delta_y);
+    frame_transform.Scale(1, scale_factor);
+  } else {
+    frame_transform.Scale(1, scale_factor);
+  }
+  gfx::Transform counter_transform;
+  CHECK(frame_transform.GetInverse(&counter_transform));
+  frame->SetTransform(frame_transform);
+
+  // Ensure that we apply the counter translation about origin of the web
+  // contents
+  gfx::Transform web_to_frame_transform;
+  web_to_frame_transform.Translate(0, -non_content_height_);
+  gfx::Transform frame_to_web_transform;
+  frame_to_web_transform.Translate(0, non_content_height_);
+  gfx::Transform web_clipping_transform = counter_transform;
+  web_clipping_transform.ConcatTransform(web_to_frame_transform);
+  web_clipping_transform.PreconcatTransform(frame_to_web_transform);
+
+  if (delta_y >= 0) {
+    web_clipping_transform.Translate(0, delta_y);
+  }
+  web_clipping_layer_->SetTransform(web_clipping_transform);
+
+  if (delta_y <= 0) {
+    gfx::Transform web_contents_transform;
+    web_contents_transform.Translate(0, delta_y);
+    web_contents_layer_->SetTransform(web_contents_transform);
+  }
+
+  gfx::Transform non_client_transform = counter_transform;
+  if (delta_y >= 0) {
+    non_client_transform.Translate(0, delta_y);
+  }
+  non_client_layer_->SetTransform(non_client_transform);
+}
+