RendererGLContext supports reparenting a GL context.

content/renderer/gpu/renderer_gl_context.cc

Index: content/renderer/gpu/renderer_gl_context.cc
===================================================================
--- content/renderer/gpu/renderer_gl_context.cc	(revision 89700)
+++ content/renderer/gpu/renderer_gl_context.cc	(working copy)
@@ -161,7 +161,7 @@
     const int32* attrib_list,
     const GURL& active_url) {
 #if defined(ENABLE_GPU)
-  scoped_ptr<RendererGLContext> context(new RendererGLContext(channel, NULL));
+  scoped_ptr<RendererGLContext> context(new RendererGLContext(channel));
   if (!context->Initialize(
       true,
       render_surface,
@@ -188,13 +188,12 @@
 
 RendererGLContext* RendererGLContext::CreateOffscreenContext(
     GpuChannelHost* channel,
-    RendererGLContext* parent,
     const gfx::Size& size,
     const char* allowed_extensions,
     const int32* attrib_list,
     const GURL& active_url) {
 #if defined(ENABLE_GPU)
-  scoped_ptr<RendererGLContext> context(new RendererGLContext(channel, parent));
+  scoped_ptr<RendererGLContext> context(new RendererGLContext(channel));
   if (!context->Initialize(
       false,
       gfx::kNullPluginWindow,
@@ -211,6 +210,42 @@
 #endif
 }
 
+bool RendererGLContext::SetParent(RendererGLContext* new_parent) {
+  // Allocate a texture ID with respect to the parent and change the parent.
+  uint32 new_parent_texture_id = 0;
+  if (new_parent) {
+    TRACE_EVENT0("gpu", "RendererGLContext::SetParent::flushParent");
+    // Flush any remaining commands in the parent context to make sure the
+    // texture id accounting stays consistent.
+    int32 token = new_parent->gles2_helper_->InsertToken();
+    new_parent->gles2_helper_->WaitForToken(token);
+    new_parent_texture_id = new_parent->gles2_implementation_->MakeTextureId();
+
+    if (!command_buffer_->SetParent(new_parent->command_buffer_,
+                                    new_parent_texture_id)) {

[piman, 2011/06/22 00:10:59]

Drive-by: since this happens out-of-band (with a message, not from the command
buffers), can this race with, say, latches ?
Case scenario:
child->SetLatch(child_to_parent)
parent1->WaitLatch(child_to_parent);
child->SetParent(parent2)
parent1->Finish()

What happens if the SetParent is executed before the SetLatch is executed ? Or
the WaitLatch ?

[apatrick_chromium, 2011/06/22 00:21:03]

It should be alright at the moment because SetParent is always called
immediately after the context is created with no latch related stuff in between.
There have been some latch related issues since this landed when trying to
create a canvas and using it to render to a window that doesn't yet exist (like
JavaScript synchronously opening a popup and then sticking a canvas in its DOM).
That doesn't work anyway though.

Going forward, I'm going to see if I can replace latches with proper glFlush /
glBindTexture semantics. I.e. call glFlush and the side effects are visible on
any other context on the channel, whether or not it was the parent at the time.

+      new_parent->gles2_implementation_->FreeTextureId(parent_texture_id_);
+      return false;
+    }
+  } else {
+    if (!command_buffer_->SetParent(NULL, 0))
+      return false;
+  }
+
+  // Free the previous parent's texture ID.
+  if (parent_.get() && parent_texture_id_ != 0)
+    parent_->gles2_implementation_->FreeTextureId(parent_texture_id_);
+
+  if (new_parent) {
+    parent_ = new_parent->AsWeakPtr();
+    parent_texture_id_ = new_parent_texture_id;
+  } else {
+    parent_.reset();
+    parent_texture_id_ = 0;
+  }
+
+  return true;
+}
+
 void RendererGLContext::ResizeOffscreen(const gfx::Size& size) {
   DCHECK(size.width() > 0 && size.height() > 0);
   if (size_ != size) {
@@ -342,11 +377,9 @@
   return gles2_implementation_;
 }
 
-RendererGLContext::RendererGLContext(GpuChannelHost* channel,
-                                     RendererGLContext* parent)
+RendererGLContext::RendererGLContext(GpuChannelHost* channel)
     : channel_(channel),
-      parent_(parent ?
-          parent->AsWeakPtr() : base::WeakPtr<RendererGLContext>()),
+      parent_(base::WeakPtr<RendererGLContext>()),
       parent_texture_id_(0),
       child_to_parent_latch_(kInvalidLatchId),
       parent_to_child_latch_(kInvalidLatchId),
@@ -377,16 +410,6 @@
   // Ensure the gles2 library is initialized first in a thread safe way.
   g_gles2_initializer.Get();
 
-  // Allocate a frame buffer ID with respect to the parent.
-  if (parent_.get()) {
-    TRACE_EVENT0("gpu", "RendererGLContext::Initialize::flushParent");
-    // Flush any remaining commands in the parent context to make sure the
-    // texture id accounting stays consistent.
-    int32 token = parent_->gles2_helper_->InsertToken();
-    parent_->gles2_helper_->WaitForToken(token);
-    parent_texture_id_ = parent_->gles2_implementation_->MakeTextureId();
-  }
-
   std::vector<int32> attribs;
   while (attrib_list) {
     int32 attrib = *attrib_list++;
@@ -431,14 +454,10 @@
           active_url);
     }
   } else {
-    CommandBufferProxy* parent_command_buffer =
-        parent_.get() ? parent_->command_buffer_ : NULL;
     command_buffer_ = channel_->CreateOffscreenCommandBuffer(
-        parent_command_buffer,
         size,
         allowed_extensions,
         attribs,
-        parent_texture_id_,
         active_url);
   }
   if (!command_buffer_) {
@@ -501,12 +520,10 @@
 
   // If this is a child context, setup latches for synchronization between child
   // and parent.
-  if (parent_.get()) {
-    if (!CreateLatch(&child_to_parent_latch_) ||
-        !CreateLatch(&parent_to_child_latch_)) {
-      Destroy();
-      return false;
-    }
+  if (!CreateLatch(&child_to_parent_latch_) ||
+      !CreateLatch(&parent_to_child_latch_)) {
+    Destroy();
+    return false;
   }
 
   // Create the object exposing the OpenGL API.
@@ -523,10 +540,7 @@
 }
 
 void RendererGLContext::Destroy() {
-  if (parent_.get() && parent_texture_id_ != 0) {
-    parent_->gles2_implementation_->FreeTextureId(parent_texture_id_);
-    parent_texture_id_ = 0;
-  }
+  SetParent(NULL);
 
   delete gles2_implementation_;
   gles2_implementation_ = NULL;