Fix a bug in drawBuffers optimization.

gpu/command_buffer/service/framebuffer_manager.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "gpu/command_buffer/service/framebuffer_manager.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include "base/logging.h"
@@ skipping 508 matching lines @@
   glDrawBuffersARB(manager_->max_draw_buffers_, adjusted_draw_buffers_.get());
 }
 
 bool Framebuffer::ValidateAndAdjustDrawBuffers(
     uint32_t fragment_output_type_mask, uint32_t fragment_output_written_mask) {
   uint32_t mask = draw_buffer_bound_mask_ & fragment_output_written_mask;
   if ((mask & fragment_output_type_mask) != (mask & draw_buffer_type_mask_))
     return false;
 
   if (mask != adjusted_draw_buffer_bound_mask_) {
-    // This won't be reached in every draw/clear call - only when framebuffer
-    // or program has changed.
+    // This won't be reached in every draw call - only when framebuffer or
+    // program has changed.
     for (uint32_t ii = 0; ii < manager_->max_draw_buffers_; ++ii) {
       adjusted_draw_buffers_[ii] = draw_buffers_[ii];
       uint32_t shift_bits = ii * 2;
       uint32_t buffer_mask = 0x3 << shift_bits;
       if ((buffer_mask & mask) == 0u) {
         adjusted_draw_buffers_[ii] = GL_NONE;
       }
     }
     adjusted_draw_buffer_bound_mask_ = mask;
     glDrawBuffersARB(manager_->max_draw_buffers_, adjusted_draw_buffers_.get());
   }
   return true;
 }
 
+void Framebuffer::AdjustDrawBuffers() {
+  if (draw_buffer_bound_mask_ == adjusted_draw_buffer_bound_mask_) {
+    return;
+  }
+  // This won't be reached in every clear call - only when framebuffer has
+  // changed.
+  for (uint32_t ii = 0; ii < manager_->max_draw_buffers_; ++ii) {
+    adjusted_draw_buffers_[ii] = draw_buffers_[ii];
+    uint32_t shift_bits = ii * 2;
+    uint32_t buffer_mask = 0x3 << shift_bits;
+    if ((buffer_mask & draw_buffer_bound_mask_) == 0u) {
+      adjusted_draw_buffers_[ii] = GL_NONE;
+    }
+  }

[Ken Russell (switch to Gerrit), 2017/01/06 22:43:07]

Per offline discussion: this is the same block of code as in
ValidateAndAdjustDrawBuffers. Could you at least refactor it into some sort of
AdjustDrawBuffersImpl and pass in draw_buffer_bound_mask_ as "mask"?

[Zhenyao Mo, 2017/01/07 00:22:24]

Done.

+  adjusted_draw_buffer_bound_mask_ = draw_buffer_bound_mask_;
+  glDrawBuffersARB(manager_->max_draw_buffers_, adjusted_draw_buffers_.get());
+}
+
 bool Framebuffer::ContainsActiveIntegerAttachments() const {
   // 0x55555555 broadcasts SHADER_VARIABLE_FLOAT to all slots.
   uint32_t mask = 0x55555555u * SHADER_VARIABLE_FLOAT;
   mask &= draw_buffer_bound_mask_;
   return draw_buffer_type_mask_ != mask;
 }
 
 void Framebuffer::ClearUnclearedIntOr3DTexturesOrPartiallyClearedTextures(
     GLES2Decoder* decoder, TextureManager* texture_manager) {
   for (AttachmentMap::const_iterator it = attachments_.begin();
@@ skipping 501 matching lines @@
 
 bool FramebufferManager::IsComplete(
     Framebuffer* framebuffer) {
   DCHECK(framebuffer);
   return framebuffer->framebuffer_complete_state_count_id() ==
       framebuffer_state_change_count_;
 }
 
 }  // namespace gles2
 }  // namespace gpu