current program can be null in ES2/ES3 contexts.

gpu/command_buffer/service/vertex_attrib_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/vertex_attrib_manager.h"
 
 #include <stdint.h>
 
 #include <list>
 
@@ skipping 109 matching lines @@
         glDeleteVertexArraysOES(1, &service_id_);
     }
     manager_->StopTracking(this);
     manager_ = NULL;
   }
 }
 
 void VertexAttribManager::Initialize(uint32_t max_vertex_attribs,
                                      bool init_attribs) {
   vertex_attribs_.resize(max_vertex_attribs);
-  max_vertex_attribs_ = max_vertex_attribs;
-  uint32_t packed_size = max_vertex_attribs_ / 16;
-  packed_size += (max_vertex_attribs_ % 16 == 0) ? 0 : 1;
+  uint32_t packed_size = max_vertex_attribs / 16;
+  packed_size += (max_vertex_attribs % 16 == 0) ? 0 : 1;

[piman, 2016/07/25 20:04:04]

nit: ditto, uint32_t packed_size = (max_vertex_attribs + 15) / 16;

   attrib_base_type_mask_.resize(packed_size);
   attrib_enabled_mask_.resize(packed_size);
 
   for (uint32_t ii = 0; ii < packed_size; ++ii) {
     attrib_enabled_mask_[ii] = 0u;
     attrib_base_type_mask_[ii] = 0u;
   }
 
   for (uint32_t vv = 0; vv < vertex_attribs_.size(); ++vv) {
     vertex_attribs_[vv].set_index(vv);
     vertex_attribs_[vv].SetList(&disabled_vertex_attribs_);
 
     if (init_attribs) {
       glVertexAttrib4f(vv, 0.0f, 0.0f, 0.0f, 1.0f);
     }
   }
 }
 
 void VertexAttribManager::SetElementArrayBuffer(Buffer* buffer) {
   element_array_buffer_ = buffer;
 }
 
 bool VertexAttribManager::Enable(GLuint index, bool enable) {
   if (index >= vertex_attribs_.size()) {
     return false;
   }
 
-  DCHECK(index < max_vertex_attribs_);
-  GLuint shift_bits = (index % 16) * 2;
-  if (enable) {
-    attrib_enabled_mask_[index / 16] |= (0x3 << shift_bits);
-  } else {
-    attrib_enabled_mask_[index / 16] &= ~(0x3 << shift_bits);
-  }
-
   VertexAttrib& info = vertex_attribs_[index];
   if (info.enabled() != enable) {
     info.set_enabled(enable);
     info.SetList(enable ? &enabled_vertex_attribs_ : &disabled_vertex_attribs_);
+    GLuint shift_bits = (index % 16) * 2;

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

We only need to do this if the glEnableDisable call actually change the state. 
This is to fit with the rest of the code - less confusing.

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

Acknowledged.

+    if (enable) {
+      attrib_enabled_mask_[index / 16] |= (0x3 << shift_bits);
+    } else {
+      attrib_enabled_mask_[index / 16] &= ~(0x3 << shift_bits);
+    }
   }
   return true;
 }
 
 void VertexAttribManager::Unbind(Buffer* buffer) {
   if (element_array_buffer_.get() == buffer) {
     element_array_buffer_ = NULL;
   }
   for (uint32_t vv = 0; vv < vertex_attribs_.size(); ++vv) {
     vertex_attribs_[vv].Unbind(buffer);
@@ skipping 112 matching lines @@
   if (current_buffer_id != kInitialBufferId) {
     // Restore the buffer binding.
     decoder->RestoreBufferBindings();
   }
 
   return true;
 }
 
 }  // namespace gles2
 }  // namespace gpu