Create an X window overlay with static ID for GL contexts.

This code creates an X window that overlays where tab contents are drawn. The handle associated with this window never changes (unlike the X window associated with a GTK widget that is created and destroyed whenever the widget is realized and unrealized respectively).  This is helpful when creating a GL context associated with an X window. Also, having a floating overlay allows us to handle detaching GPU accelerated tabs.

This code seems to have uncovered a race condition within the GPU process. When a tab that uses accelerated compositing is detached (e.g. http://webkit.org/blog/386/3d-transforms/), the tab contents often don't get displayed even though the tab is redrawn.  A slight delay of about 100ms in the GPU process on the call to glXSwapBuffers (in gl_context_linux.cc) fixes this. To witness that GL can draw to the overlay after delay, try it with a tab with constant animation (e.g. http://webkit.org/blog-files/3d-transforms/poster-circle.html).

I've written a bare bones test (about 150 lines of C) of the overlay technique, and it requires no such delay b/w reparenting the glXSwapBuffers. I've also confirmed that there is no synchronization issues w.r.t. the X server between my patch and GL draw commands. I propose filing a new bug for the race, if this patch gets accepted.

BUG=53345,56419
TEST=Open two tabs, one with GPU rendered content (http://webkit.org/blog/386/3d-transforms/). Detach the tab with GPU rendered content.  GPU process shouldn't crash.

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=61561

Review URL: http://codereview.chromium.org/3509004
Patch from Jonathan Backer <backer@google.com>.

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@61695 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 22 insertions, 4 deletions

diff --git a/gfx/gtk_native_view_id_manager.h b/gfx/gtk_native_view_id_manager.h
index 0a90e2f..439d843 100644
--- a/gfx/gtk_native_view_id_manager.h
+++ b/gfx/gtk_native_view_id_manager.h
@@ -6,6 +6,7 @@
 #define GFX_GTK_NATIVE_VIEW_ID_MANAGER_H_
 #pragma once
 
+#include <gtk/gtk.h>
 #include <map>
 
 #include "base/singleton.h"
@@ -59,10 +60,27 @@ class GtkNativeViewManager {
   // |*xid| is set to 0.
   bool GetXIDForId(XID* xid, gfx::NativeViewId id);
 
+  // Generate an XID that doesn't change.
+  //
+  // The GPU process assumes that the XID associated with a GL context
+  // does not change. To maintain this invariant we create and overlay
+  // whose XID is static. This requires reparenting as the underlying
+  // window comes and goes.  It incurs a bit of overhead, so a permanent
+  // XID must be requested.
+  //
+  // Must be called from the UI thread so that the widget that we
+  // overlay does not change while we construct the overlay.
+  //
+  // xid: (output) the resulting X window
+  // id: a value previously returned from GetIdForWidget
+  // returns: true if |id| is a valid id, false otherwise.
+  bool GetPermanentXIDForId(XID* xid, gfx::NativeViewId id);
+
   // These are actually private functions, but need to be called from statics.
   void OnRealize(gfx::NativeView widget);
   void OnUnrealize(gfx::NativeView widget);
   void OnDestroy(gfx::NativeView widget);
+  void OnSizeAllocate(gfx::NativeView widget, GtkAllocation *alloc);
 
   Lock& unrealize_lock() { return unrealize_lock_; }
 
@@ -73,11 +91,11 @@ class GtkNativeViewManager {
   friend struct DefaultSingletonTraits<GtkNativeViewManager>;
 
   struct NativeViewInfo {
-    NativeViewInfo()
-        : x_window_id(0) {
-    }
-
+    NativeViewInfo() : x_window_id(0), permanent_window_id(0) { }
+    // XID associated with GTK widget.
     XID x_window_id;
+    // Permanent overlay (0 if not requested yet).
+    XID permanent_window_id;
   };
 
   gfx::NativeViewId GetWidgetId(gfx::NativeView id);