X11: Avoid round-tripping to get the cursor position

This is a performance optimization which avoids calling XQueryPointer
when we're dispatching a mouse event.  It's become a convenience to
call GetCursorScreenPoint() all over the place in Chrome, even when an
event which has the cursor position is available.

R=sadrul@chromium.org

Review-Url: https://codereview.chromium.org/2398343002
Cr-Commit-Position: refs/heads/master@{#424645}

ui/events/platform/x11/x11_event_source.cc

@@ -96,7 +96,6 @@ X11EventSource::X11EventSource(X11EventSourceDelegate* delegate,
                                XDisplay* display)
     : delegate_(delegate),
       display_(display),
-      event_timestamp_(CurrentTime),
       dummy_initialized_(false),
       continue_stream_(true) {
   DCHECK(!instance_);
@@ -184,13 +183,43 @@ Time X11EventSource::GetCurrentServerTime() {
 }
 
 Time X11EventSource::GetTimestamp() {
-  if (event_timestamp_ != CurrentTime) {
+  if (!dispatching_events_.empty()) {
-    return event_timestamp_;
+    DCHECK(dispatching_events_.top());
+    Time timestamp = ExtractTimeFromXEvent(*dispatching_events_.top());
+    if (timestamp != CurrentTime)
+      return timestamp;
   }
   DVLOG(1) << "Making a round trip to get a recent server timestamp.";
   return GetCurrentServerTime();
 }
 
+base::Optional<gfx::Point>
+X11EventSource::GetRootCursorLocationFromCurrentEvent() const {
+  if (dispatching_events_.empty())
+    return base::nullopt;
+
+  XEvent* event = dispatching_events_.top();
+  DCHECK(event);
+  bool is_valid_event = false;
+  switch (event->type) {
+    case ButtonPress:
+    case ButtonRelease:
+    case MotionNotify:
+    case EnterNotify:
+    case LeaveNotify:
+      is_valid_event = true;
+      break;
+    case GenericEvent:
+      if (!ui::TouchFactory::GetInstance()->ShouldProcessXI2Event(event))
+        break;
+      is_valid_event = true;
+  }
+
+  if (is_valid_event)
+    return ui::EventSystemLocationFromNative(event);
+  return base::nullopt;
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // X11EventSource, protected
 
@@ -201,12 +230,12 @@ void X11EventSource::ExtractCookieDataDispatchEvent(XEvent* xevent) {
     have_cookie = true;
   }
 
-  event_timestamp_ = ExtractTimeFromXEvent(*xevent);
+  dispatching_events_.push(xevent);
 
   delegate_->ProcessXEvent(xevent);
   PostDispatchEvent(xevent);
 
-  event_timestamp_ = CurrentTime;
+  dispatching_events_.pop();
 
   if (have_cookie)
     XFreeEventData(xevent->xgeneric.display, &xevent->xcookie);

ui/events/platform/x11/x11_event_source.h

@@ -8,8 +8,10 @@
 #include <stdint.h>
 
 #include <memory>
+#include <stack>
 
 #include "base/macros.h"
+#include "base/optional.h"
 #include "ui/events/events_export.h"
 #include "ui/gfx/x/x11_types.h"
 
@@ -18,6 +20,10 @@ using XEvent = union _XEvent;
 using XID = unsigned long;
 using XWindow = unsigned long;
 
+namespace gfx {
+class Point;
+}
+
 namespace ui {
 
 class X11HotplugEventHandler;
@@ -77,6 +83,10 @@ class EVENTS_EXPORT X11EventSource {
   // current event does not have a timestamp.
   Time GetTimestamp();
 
+  // Returns the root pointer location only if there is an event being
+  // dispatched that contains that information.
+  base::Optional<gfx::Point> GetRootCursorLocationFromCurrentEvent() const;
+
   void StopCurrentEventStream();
   void OnDispatcherListChanged();
 
@@ -105,8 +115,9 @@ class EVENTS_EXPORT X11EventSource {
   // The connection to the X11 server used to receive the events.
   XDisplay* display_;
 
-  // The timestamp of the event being dispatched.
+  // Events currently being dispatched.  The topmost event in this stack
-  Time event_timestamp_;
+  // corresponds to the deepest-nested message loop.
+  std::stack<XEvent*> dispatching_events_;
 
   // State necessary for UpdateLastSeenServerTime
   bool dummy_initialized_;

ui/views/widget/desktop_aura/desktop_screen_x11.cc

@@ -22,6 +22,7 @@
 #include "ui/display/util/display_util.h"
 #include "ui/display/util/x11/edid_parser_x11.h"
 #include "ui/events/platform/platform_event_source.h"
+#include "ui/events/platform/x11/x11_event_source.h"
 #include "ui/gfx/font_render_params.h"
 #include "ui/gfx/geometry/point_conversions.h"
 #include "ui/gfx/geometry/size_conversions.h"
@@ -133,20 +134,18 @@ DesktopScreenX11::~DesktopScreenX11() {
 gfx::Point DesktopScreenX11::GetCursorScreenPoint() {
   TRACE_EVENT0("views", "DesktopScreenX11::GetCursorScreenPoint()");
 
-  XDisplay* display = gfx::GetXDisplay();
+  if (ui::X11EventSource::HasInstance()) {
+    auto point = ui::X11EventSource::GetInstance()
+                     ->GetRootCursorLocationFromCurrentEvent();
+    if (point)
+      return point.value();
+  }
 
   ::Window root, child;
   int root_x, root_y, win_x, win_y;
   unsigned int mask;
-  XQueryPointer(display,
+  XQueryPointer(xdisplay_, x_root_window_, &root, &child, &root_x, &root_y,
-                DefaultRootWindow(display),
+                &win_x, &win_y, &mask);
-                &root,
-                &child,
-                &root_x,
-                &root_y,
-                &win_x,
-                &win_y,
-                &mask);
 
   return PixelToDIPPoint(gfx::Point(root_x, root_y));
 }