Ink drops with touch input are redundant on Windows since the OS does something similar

ui/views/animation/ink_drop_host_view.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 "ui/views/animation/ink_drop_host_view.h"
 
 #include "ui/events/event.h"
 #include "ui/events/scoped_target_handler.h"
 #include "ui/gfx/color_palette.h"
 #include "ui/gfx/geometry/size_conversions.h"
@@ skipping 154 matching lines @@
 }
 
 gfx::Point InkDropHostView::GetInkDropCenterBasedOnLastEvent() const {
   return last_ripple_triggering_event_
              ? last_ripple_triggering_event_->location()
              : GetLocalBounds().CenterPoint();
 }
 
 void InkDropHostView::AnimateInkDrop(InkDropState state,
                                      const ui::LocatedEvent* event) {
+#if defined(OS_WIN)
+  if ((state == InkDropState::ACTION_PENDING ||

[sky, 2016/06/24 19:21:11]

Is there a reason why you care about the state in this case? Isn't the event
enough?

[Evan Stade, 2016/06/24 20:28:30]

I imagine this is to handle cases like if you were to press down with the mouse
then tap the view before releasing the mouse button?

I'd go for simpler code instead of trying to support a crazy use case like this,
unless the simpler code makes things look totally broken. Either way, docs would
be nice because this block is hard to grok.

[kylix_rd, 2016/06/24 20:32:18]

Only certain states or actions should be allowed to propagate when the event
source is touch (or gestures). Because Windows provides its own touch feedback
that is similar to the ink-drop feedback, it is favored. Only when the ink is
already present (from a mouse-click or focus event) should the state be
transitioned regardless of the event source.

At least that is my understanding of the requirement.

+       state == InkDropState::ALTERNATE_ACTION_PENDING ||
+       ((state == InkDropState::ACTION_TRIGGERED ||
+         state == InkDropState::ALTERNATE_ACTION_TRIGGERED) &&
+        ink_drop_->GetTargetInkDropState() == InkDropState::HIDDEN)) &&
+      event && event->IsGestureEvent())
+    return;
+#endif
   last_ripple_triggering_event_.reset(
       event ? ui::Event::Clone(*event).release()->AsLocatedEvent() : nullptr);
   ink_drop_->AnimateToState(state);
 }
 
 void InkDropHostView::VisibilityChanged(View* starting_from, bool is_visible) {
   View::VisibilityChanged(starting_from, is_visible);
   if (GetWidget() && !is_visible) {
     ink_drop()->AnimateToState(InkDropState::HIDDEN);
     ink_drop()->SetHovered(false);
@@ skipping 39 matching lines @@
   if (has_an_ink_drop) {
     ink_drop_.reset(new InkDropImpl(this));
     gesture_handler_.reset(new InkDropGestureHandler(this, ink_drop_.get()));
   } else {
     gesture_handler_.reset();
     ink_drop_.reset(new InkDropStub());
   }
 }
 
 }  // namespace views