Restore gl scissor state when switching FBO targets on Qualcomm

ui/gl/gl_gl_api_implementation.cc

Index: ui/gl/gl_gl_api_implementation.cc
diff --git a/ui/gl/gl_gl_api_implementation.cc b/ui/gl/gl_gl_api_implementation.cc
index 672f1ea47473ec8e1b1d43b922f9c0c68dda102b..d9f5f63e59146318b4e41ce295be85256d8f903c 100644
--- a/ui/gl/gl_gl_api_implementation.cc
+++ b/ui/gl/gl_gl_api_implementation.cc
@@ -112,9 +112,9 @@ void VirtualGLApi::Initialize(DriverGL* driver, GLContext* real_context) {
 
 bool VirtualGLApi::MakeCurrent(GLContext* virtual_context, GLSurface* surface) {
   bool switched_contexts = g_current_gl_context != this;
-  GLSurface* current_surface = GLSurface::GetCurrent();
-  if (switched_contexts || surface != current_surface) {
-    if (!switched_contexts && current_surface &&
+  bool switched_surfaces = GLSurface::GetCurrent() != surface;

[brianderson, 2013/01/04 22:00:56]

Note:

This comparison is almost always false because I'm comparing the "real" surface
to the "virtual" surface, so this patch almost always restores the state on a
MakeCurrent.

That's a bit more often than I intended.

Other parts of the function compare these two surfaces though, which is where my
confusion came from.

Will need to figure out how to narrow down which case we need to restore the
state.  I'm not sure it's easy to detect FBO target changes from here.  Even if
we could detect it here, it'll probably be too late.

+  if (switched_contexts || switched_surfaces) {
+    if (!switched_contexts && GLSurface::GetCurrent() &&
         virtual_context->IsCurrent(surface)) {
       // MakeCurrent 'lite' path that avoids potentially expensive MakeCurrent()
       // calls if the GLSurface uses the same underlying surface or renders to
@@ -132,7 +132,13 @@ bool VirtualGLApi::MakeCurrent(GLContext* virtual_context, GLSurface* surface) {
   DCHECK(real_context_->IsCurrent(GLSurface::GetCurrent()));
   DCHECK(virtual_context->IsCurrent(surface));
 
-  if (switched_contexts || virtual_context != current_context_) {
+  // This work around restores gl state on virtual context switches
+  // where only the surface changes.
+  bool qualcomm_WAR_enabled = true;  // TODO: Set this only when needed.
+  bool use_qualcomm_WAR = qualcomm_WAR_enabled && switched_surfaces;
+
+  if (switched_contexts || virtual_context != current_context_ ||
+      use_qualcomm_WAR) {
     // There should be no errors from the previous context leaking into the
     // new context.
     DCHECK_EQ(glGetErrorFn(), static_cast<GLenum>(GL_NO_ERROR));