command_buffer: Implement EXT_blend_func_extended

gpu/command_buffer/service/context_group.cc

Index: gpu/command_buffer/service/context_group.cc
diff --git a/gpu/command_buffer/service/context_group.cc b/gpu/command_buffer/service/context_group.cc
index 04bff52c51f8f3bad599c03c1f4a39bdc8fda89f..9d8cee05a726f218a22daedf6116771d425e7e7d 100644
--- a/gpu/command_buffer/service/context_group.cc
+++ b/gpu/command_buffer/service/context_group.cc
@@ -68,6 +68,7 @@ ContextGroup::ContextGroup(
       max_vertex_uniform_vectors_(0u),
       max_color_attachments_(1u),
       max_draw_buffers_(1u),
+      max_dual_source_draw_buffers_(0u),
       program_cache_(NULL),
       feature_info_(feature_info) {
   {
@@ -144,6 +145,12 @@ bool ContextGroup::Initialize(
     if (max_draw_buffers_ < 1)
       max_draw_buffers_ = 1;
   }
+  if (feature_info_->feature_flags().ext_blend_func_extended) {
+    GetIntegerv(GL_MAX_DUAL_SOURCE_DRAW_BUFFERS,
+                &max_dual_source_draw_buffers_);
+    if (max_dual_source_draw_buffers_ < 1)
+      max_dual_source_draw_buffers_ = 0;

[Mark Kilgard, 2015/08/28 19:53:24]

Context: just to set expectations, the value of GL_MAX_DUAL_SOURCE_DRAW_BUFFERS
is 1 for all GPUs which I am aware (NVIDIA or otherwise).

In other words, this functionality isn't really orthogonal to multiple render
targets.

This kind of makes sense because source two colors for the blend function is a
different way of using multiple shader color outputs that writing to multiple
color buffers.

+  }
 
   buffer_manager_.reset(
       new BufferManager(memory_tracker_.get(), feature_info_.get()));
@@ -290,8 +297,9 @@ bool ContextGroup::Initialize(
 
   path_manager_.reset(new PathManager());
 
-  program_manager_.reset(new ProgramManager(
-      program_cache_, max_varying_vectors_, feature_info_.get()));
+  program_manager_.reset(
+      new ProgramManager(program_cache_, max_varying_vectors_,
+                         max_dual_source_draw_buffers_, feature_info_.get()));
 
   if (!texture_manager_->Initialize()) {
     LOG(ERROR) << "Context::Group::Initialize failed because texture manager "