Controls offsets computed if either top or bottom are showing

cc/input/browser_controls_offset_manager.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 "cc/input/browser_controls_offset_manager.h"
 
 #include <stdint.h>
 
 #include <algorithm>
 
@@ skipping 25 matching lines @@
 BrowserControlsOffsetManager::BrowserControlsOffsetManager(
     BrowserControlsOffsetManagerClient* client,
     float controls_show_threshold,
     float controls_hide_threshold)
     : client_(client),
       animation_start_value_(0.f),
       animation_stop_value_(0.f),
       animation_direction_(NO_ANIMATION),
       permitted_state_(BOTH),
       accumulated_scroll_delta_(0.f),
-      baseline_content_offset_(0.f),
+      baseline_top_content_offset_(0.f),
+      baseline_bottom_content_offset_(0.f),
       controls_show_threshold_(controls_hide_threshold),
       controls_hide_threshold_(controls_show_threshold),
       pinch_gesture_active_(false) {
   CHECK(client_);
 }
 
 BrowserControlsOffsetManager::~BrowserControlsOffsetManager() {}
 
 float BrowserControlsOffsetManager::ControlsTopOffset() const {
   return ContentTopOffset() - TopControlsHeight();
@@ skipping 56 matching lines @@
 void BrowserControlsOffsetManager::ScrollBegin() {
   if (pinch_gesture_active_)
     return;
 
   ResetAnimations();
   ResetBaseline();
 }
 
 gfx::Vector2dF BrowserControlsOffsetManager::ScrollBy(
     const gfx::Vector2dF& pending_delta) {
-  if (!TopControlsHeight())
+  // If one or both of the top/bottom controls are showing, the shown ratio
+  // needs to be computed.
+  float controls_height =
+      TopControlsHeight() ? TopControlsHeight() : BottomControlsHeight();
+
+  if (!controls_height)
     return pending_delta;
 
   if (pinch_gesture_active_)
     return pending_delta;
 
   if (permitted_state_ == SHOWN && pending_delta.y() > 0)
     return pending_delta;
   else if (permitted_state_ == HIDDEN && pending_delta.y() < 0)
     return pending_delta;
 
   accumulated_scroll_delta_ += pending_delta.y();
 
-  float old_offset = ContentTopOffset();
+  float old_top_offset = ContentTopOffset();
+  float baseline_content_offset = TopControlsHeight()
+      ? baseline_top_content_offset_ : baseline_bottom_content_offset_;
   client_->SetCurrentBrowserControlsShownRatio(
-      (baseline_content_offset_ - accumulated_scroll_delta_) /
-      TopControlsHeight());
+      (baseline_content_offset - accumulated_scroll_delta_) / controls_height);
 
   // If the controls are fully visible, treat the current position as the
   // new baseline even if the gesture didn't end.
   if (TopControlsShownRatio() == 1.f)
     ResetBaseline();
 
   ResetAnimations();
 
-  gfx::Vector2dF applied_delta(0.f, old_offset - ContentTopOffset());
+  // applied_delta will negate any scroll on the content if the top browser
+  // controls are showing in favor of hiding the controls and resizing the
+  // content. If the top controls have no height, the content should scroll
+  // immediately.
+  gfx::Vector2dF applied_delta(0.f,
+      TopControlsHeight() ? old_top_offset - ContentTopOffset() : 0.0f);
   return pending_delta - applied_delta;
 }
 
 void BrowserControlsOffsetManager::ScrollEnd() {
   if (pinch_gesture_active_)
     return;
 
   StartAnimationIfNecessary();
 }
 
@@ skipping 22 matching lines @@
 
   float old_offset = ContentTopOffset();
   float new_ratio = gfx::Tween::ClampedFloatValueBetween(
       monotonic_time, animation_start_time_, animation_start_value_,
       animation_stop_time_, animation_stop_value_);
   client_->SetCurrentBrowserControlsShownRatio(new_ratio);
 
   if (IsAnimationComplete(new_ratio))
     ResetAnimations();
 
-  gfx::Vector2dF scroll_delta(0.f, ContentTopOffset() - old_offset);
+  // Don't move the content if the top controls aren't used.
+  gfx::Vector2dF scroll_delta(0.f,
+      TopControlsHeight() ? (ContentTopOffset() - old_offset) : 0.0f);

[aelias_OOO_until_Jul13, 2016/11/04 04:24:50]

ContentTopOffset() method name is now a lie (it doesn't affect content top
offset at all when only bottom controls are present) and you have a bit of
duplicated logic here.

So I suggest introducing a new method called VisibleControlsHeight which has the
exact same implementation as ContentTopOffset() does today.  Then change
ContentTopOffset() implementation to be { TopControlsHeight() ?
VisibleControlsHeight() : 0.f }

[mdjones, 2016/11/05 00:17:26]

I'm not sure I understand what you mean. In the case that only the bottom
controls are showing, ContentTopOffset will correctly return 0. The proposed
change would still result in me needing the logic for scroll_delta.

[aelias_OOO_until_Jul13, 2016/11/05 00:47:15]

OK, right.  Well, the source of my confusion is that assumed you made the change
here in order to fix a bug and drew a logical conclusion without actually
looking again at ContentTopOffset() implementation :).  Maybe you only added the
extra unnecessary complexity for some principle of cleanliness -- if so, I don't
agree with that principle, I prefer code to have as few branches as possible.

[mdjones, 2016/11/07 17:14:45]

Done, added logic to ContentTopOffset and ContentBottomOffset to return 0 if
their respective heights are 0.

   return scroll_delta;
 }
 
 void BrowserControlsOffsetManager::ResetAnimations() {
   animation_start_time_ = base::TimeTicks();
   animation_start_value_ = 0.f;
   animation_stop_time_ = base::TimeTicks();
   animation_stop_value_ = 0.f;
 
   animation_direction_ = NO_ANIMATION;
@@ skipping 46 matching lines @@
   }
 }
 
 bool BrowserControlsOffsetManager::IsAnimationComplete(float new_ratio) {
   return (animation_direction_ == SHOWING_CONTROLS && new_ratio >= 1.f) ||
          (animation_direction_ == HIDING_CONTROLS && new_ratio <= 0.f);
 }
 
 void BrowserControlsOffsetManager::ResetBaseline() {
   accumulated_scroll_delta_ = 0.f;
-  baseline_content_offset_ = ContentTopOffset();
+  baseline_top_content_offset_ = ContentTopOffset();
+  baseline_bottom_content_offset_ = ContentBottomOffset();
 }
 
 }  // namespace cc