command_buffer: Implement EXT_blend_func_extended

Implement EXT_blend_func_extended for command buffer ES 2.0 and ES 3.0
contexts.

For the ES 2.0 context, the extension supports dual-source blending with
pre-defined gl_SecondaryFragColorEXT and gl_SecondaryFragDataEXT
variables.

Currently EXT_blend_func_extended is only exposed if the service context
supports program interface query. This means OpenGL context or OpenGL
ES 3.1 context. This is to simplify the unit test expectation conditions.
Theoretically also ES 2.0 and ES 3.0 service contexts could support
EXT_blend_func_extended, but probably there will never be such a driver.

BUG=506765

Review URL: https://codereview.chromium.org/1309743005

Cr-Commit-Position: refs/heads/master@{#363175}

1 files changed, 5 insertions, 0 deletions

diff --git a/gpu/command_buffer/service/context_group.h b/gpu/command_buffer/service/context_group.h
index ad2c5df..fa9d3ac 100644
--- a/gpu/command_buffer/service/context_group.h
+++ b/gpu/command_buffer/service/context_group.h
@@ -123,6 +123,10 @@ class GPU_EXPORT ContextGroup : public base::RefCounted<ContextGroup> {
     return max_draw_buffers_;
   }
 
+  uint32 max_dual_source_draw_buffers() const {
+    return max_dual_source_draw_buffers_;
+  }
+
   FeatureInfo* feature_info() {
     return feature_info_.get();
   }
@@ -271,6 +275,7 @@ class GPU_EXPORT ContextGroup : public base::RefCounted<ContextGroup> {
   uint32 max_vertex_uniform_vectors_;
   uint32 max_color_attachments_;
   uint32 max_draw_buffers_;
+  uint32 max_dual_source_draw_buffers_;
 
   ProgramCache* program_cache_;