Fixes rounding error when calculating MOVE event

components/exo/pointer.cc

 // Copyright 2015 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 "components/exo/pointer.h"
 
+#include <utility>

[reveman, 2017/05/25 23:59:12]

why was this needed?

+
 #include "ash/public/cpp/shell_window_ids.h"
 #include "cc/output/copy_output_request.h"
 #include "cc/output/copy_output_result.h"
 #include "components/exo/pointer_delegate.h"
 #include "components/exo/pointer_stylus_delegate.h"
 #include "components/exo/surface.h"
 #include "components/exo/wm_helper.h"
 #include "ui/aura/client/cursor_client.h"
 #include "ui/aura/env.h"
 #include "ui/aura/window.h"
 #include "ui/display/manager/display_manager.h"
 #include "ui/display/manager/managed_display_info.h"
 #include "ui/display/screen.h"
 #include "ui/events/event.h"
 #include "ui/gfx/geometry/vector2d_conversions.h"
 #include "ui/gfx/transform_util.h"
 
 #if defined(USE_OZONE)
 #include "ui/ozone/public/cursor_factory_ozone.h"
 #endif
 
 #if defined(USE_X11)
 #include "ui/base/cursor/cursor_loader_x11.h"
 #endif
 
 namespace exo {
 namespace {
 
 const float kLargeCursorScale = 2.8f;
+const double kLocatedEventEpsilonSquared = 1.0 / (2000.0 * 2000.0);
 
 // Synthesized events typically lack floating point precision so to avoid
 // generating mouse event jitter we consider the location of these events
 // to be the same as |location| if floored values match.
 bool SameLocation(const ui::LocatedEvent* event, const gfx::PointF& location) {
   if (event->flags() & ui::EF_IS_SYNTHESIZED)
     return event->location() == gfx::ToFlooredPoint(location);
 
-  return event->location_f() == location;
+  // In general, it is good practice to compare floats using an epsilon.
+  // In particular, the mouse location_f() could differ between the
+  // MOUSE_PRESSED and MOUSE_RELEASED events. At MOUSE_RELEASED, it will have a
+  // targeter() already cached, while at MOUSE_PRESSED, it will have to
+  // calculate it passing through all the hierarchy of windows, and that could
+  // generate rounding error. std::numeric_limits<float>::epsilon() is not big
+  // enough to catch this rounding error.
+  gfx::Vector2dF offset = event->location_f() - location;
+  return offset.LengthSquared() < (2 * kLocatedEventEpsilonSquared);
 }
 
 }  // namespace
 
 ////////////////////////////////////////////////////////////////////////////////
 // Pointer, public:
 
 Pointer::Pointer(PointerDelegate* delegate)
     : delegate_(delegate),
       cursor_(ui::CursorType::kNull),
@@ skipping 340 matching lines @@
   if (!root_window)
     return;
 
   aura::client::CursorClient* cursor_client =
       aura::client::GetCursorClient(root_window);
   if (cursor_client)
     cursor_client->SetCursor(cursor_);
 }
 
 }  // namespace exo