aura-x11: Add custom web cursor support.

ui/aura/root_window_host_linux.cc

Index: ui/aura/root_window_host_linux.cc
diff --git a/ui/aura/root_window_host_linux.cc b/ui/aura/root_window_host_linux.cc
index 57f6394bfef26de22d21c9eb358a00656ce8303b..dcbc0bfb7b87ccbe37d112dfd8208fa4a7a34f2c 100644
--- a/ui/aura/root_window_host_linux.cc
+++ b/ui/aura/root_window_host_linux.cc
@@ -152,9 +152,11 @@ int CursorShapeFromNative(gfx::NativeCursor native_cursor) {
     case aura::kCursorZoomOut:
     case aura::kCursorGrab:
     case aura::kCursorGrabbing:
-    case aura::kCursorCustom:
       // TODO(jamescook): Need cursors for these.  crbug.com/111650
       return XC_left_ptr;
+    case aura::kCursorCustom:
+      NOTREACHED();
+      return XC_left_ptr;
   }
   NOTREACHED();
   return XC_left_ptr;
@@ -273,6 +275,7 @@ RootWindowHostLinux::RootWindowHostLinux(const gfx::Rect& bounds)
       xwindow_(0),
       x_root_window_(DefaultRootWindow(xdisplay_)),
       current_cursor_(aura::kCursorNull),
+      custom_cursor_(0),
       cursor_shown_(true),
       bounds_(bounds) {
   XSetWindowAttributes swa;
@@ -550,6 +553,16 @@ void RootWindowHostLinux::SetCursor(gfx::NativeCursor cursor) {
     SetCursorInternal(cursor);
 }
 
+void RootWindowHostLinux::SetCustomCursor(const gfx::PlatformCursor& cursor) {
+  if (custom_cursor_)
+    ui::UnrefCustomXCursor(custom_cursor_);

[Daniel Erat, 2012/02/24 21:04:36]

put this in the d'tor too

[sadrul, 2012/02/24 22:48:49]

Ah, good catch. Done.

+  custom_cursor_ = cursor;
+  if (custom_cursor_)
+    ui::RefCustomXCursor(custom_cursor_);
+  if (cursor_shown_)
+    XDefineCursor(xdisplay_, xwindow_, cursor);

[Daniel Erat, 2012/02/24 21:04:36]

i think that you need to make ShowCursor() handle the custom-cursor case too. 
what about something like the following?

- make SetCustomCursor() set custom_cursor_ to the passed-in cursor, set
current_cursor_ to kCursorCustom, and (if cursor_shown_ is true) call
SetCursorInternal(kCursorCustom)
- make SetCursorInternal() use custom_cursor_ (after CHECK()-ing that it's not
0) for the kCursorCustom case
- get rid of the cursor-unref-ing in SetCursorInternal(), and only unref in the
d'tor, SetCustomCursor(), and SetCursor()

[sadrul, 2012/02/24 22:48:49]

Very nice. Done!

One exception: I am not CHECK()ing in SetCursor for cursor != kCursorCustom.
This is because RootWindowEventFilter essentially does
root->SetCursor(target->GetCursor()). Doing this correctly in RWEF will involve
adding a corresponding GetCustomCursor on aura::Window, WindowDelegate, and
ref/unref-ing the custom cursor in RWEF (for a
|custom_cursor_to_set_on_unlock_|). I feel like that's bordering on too much
complication, and so decided against it.

[Daniel Erat, 2012/02/24 23:19:31]

Hmm, I see.  Will the current unsetting/unref-ing of custom_cursor_ in
SetCursor() cause problems here, since the custom cursor will be gone when we
try to restore it later?  Perhaps the old custom cursor should only be thrown
away in SetCustomCursor().

[sadrul, 2012/02/25 00:02:30]

I have changed the code in SetCursor to unset custom_cursor_ only if it wasn't
called with kCursorCustom.

[Daniel Erat, 2012/02/25 00:38:56]

So just to make sure that I understand correctly, is it now safe for
SetCursor(kCursorCustom) to be called even if custom_cursor_ is 0?  Or can this
never happen?  It seems like it can, if RootWindowEventFilter::UpdateCursor()
tries to set a custom cursor while the cursor is locked, but maybe this is
avoided for some other reason (I'm not familiar with RWEF).

+}
+
 void RootWindowHostLinux::ShowCursor(bool show) {
   if (show == cursor_shown_)
     return;
@@ -647,6 +660,10 @@ void RootWindowHostLinux::SetCursorInternal(gfx::NativeCursor cursor) {
       invisible_cursor_ :
       ui::GetXCursor(CursorShapeFromNative(cursor));
   XDefineCursor(xdisplay_, xwindow_, xcursor);
+  if (custom_cursor_) {
+    ui::UnrefCustomXCursor(custom_cursor_);
+    custom_cursor_ = 0;
+  }
 }
 
 // static