current program can be null in ES2/ES3 contexts.

gpu/command_buffer/service/program_manager.h

 // 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.
 
 #ifndef GPU_COMMAND_BUFFER_SERVICE_PROGRAM_MANAGER_H_
 #define GPU_COMMAND_BUFFER_SERVICE_PROGRAM_MANAGER_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 379 matching lines @@
     return transform_feedback_varyings_;
   }
 
   GLenum transform_feedback_buffer_mode() const {
     return transform_feedback_buffer_mode_;
   }
 
   // See member declaration for details.
   // The data are only valid after a successful link.
   uint32_t fragment_output_type_mask() const {
-      return fragment_output_type_mask_;
+    return fragment_output_type_mask_;
   }
   uint32_t fragment_output_written_mask() const {
-      return fragment_output_written_mask_;
+    return fragment_output_written_mask_;
   }
 
   // The data are only valid after a successful link.
-  // Return 16 attributes' base types, in which the attribute
-  // specified by argument 'loc' located.
-  uint32_t vertex_input_base_type_mask(GLuint loc) const {
-      DCHECK(loc < max_vertex_attribs_);
-      return vertex_input_base_type_mask_[loc / 16];
+  const std::vector<uint32_t>& vertex_input_base_type_mask() const {
+    return vertex_input_base_type_mask_;
   }
-  // Return 16 attributes' type written masks, in which the
-  // attribute specified by argument 'loc' located.
-  uint32_t vertex_input_type_written_mask(GLuint loc) const {
-      DCHECK(loc < max_vertex_attribs_);
-      return vertex_input_type_written_mask_[loc / 16];
+  const std::vector<uint32_t>& vertex_input_active_mask() const {
+    return vertex_input_active_mask_;
   }
 
   // Update uniform block binding after a successful glUniformBlockBinding().
   void SetUniformBlockBinding(GLuint index, GLuint binding);
 
   const std::vector<UniformBlockSizeInfo>& uniform_block_size_info() const {
     return uniform_block_size_info_;
   }
 
  private:
@@ skipping 69 matching lines @@
     return static_cast<size_t>(fake_location & 0xFFFF);
   }
 
   static inline size_t GetArrayElementIndexFromFakeLocation(
       GLint fake_location) {
     return static_cast<size_t>((fake_location >> 16) & 0xFFFF);
   }
 
   const FeatureInfo& feature_info() const;
 
+  void ClearVertexInputMasks();
+
   ProgramManager* manager_;
 
   int use_count_;
 
   GLsizei max_attrib_name_length_;
 
   // Attrib by index.
   AttribInfoVector attrib_infos_;
 
   // Attrib by location to index.
@@ skipping 57 matching lines @@
   std::vector<UniformBlockSizeInfo> uniform_block_size_info_;
 
   // Fragment output variable base types: FLOAT, INT, or UINT.
   // We have up to 16 outputs, each is encoded into 2 bits, total 32 bits:
   // the lowest 2 bits for location 0, the highest 2 bits for location 15.
   uint32_t fragment_output_type_mask_;
   // Same layout as above, 2 bits per location, 0x03 if a location is occupied
   // by an output variable, 0x00 if not.
   uint32_t fragment_output_written_mask_;
 
-  uint32_t max_vertex_attribs_;
   // Vertex input attrib base types: FLOAT, INT, or UINT.
   // Each base type is encoded into 2 bits, the lowest 2 bits for location 0,
-  // the highest 2 bits for location (max_vertex_attribs_ - 1).
+  // the highest 2 bits for location (max_vertex_attribs - 1).
   std::vector<uint32_t> vertex_input_base_type_mask_;
   // Same layout as above, 2 bits per location, 0x03 if a location is set
   // by vertexAttrib API, 0x00 if not.
-  std::vector<uint32_t> vertex_input_type_written_mask_;
+  std::vector<uint32_t> vertex_input_active_mask_;

[Zhenyao Mo, 2016/07/23 16:10:40]

I think this is a better name, since we don't write to the attribs in vertex
shader like the fragment output variables.

[yunchao, 2016/07/24 04:52:13]

Agreed!

 };
 
 // Tracks the Programs.
 //
 // NOTE: To support shared resources an instance of this class will
 // need to be shared by multiple GLES2Decoders.
 class GPU_EXPORT ProgramManager {
  public:
   ProgramManager(ProgramCache* program_cache,
                  uint32_t max_varying_vectors,
@@ skipping 87 matching lines @@
 };
 
 inline const FeatureInfo& Program::feature_info() const {
   return *manager_->feature_info_.get();
 }
 
 }  // namespace gles2
 }  // namespace gpu
 
 #endif  // GPU_COMMAND_BUFFER_SERVICE_PROGRAM_MANAGER_H_