[Command buffer] Enable primitive restart for WebGL 2

gpu/command_buffer/service/buffer_manager.cc

Index: gpu/command_buffer/service/buffer_manager.cc
diff --git a/gpu/command_buffer/service/buffer_manager.cc b/gpu/command_buffer/service/buffer_manager.cc
index 914d9b09da06e8fb3a71c2162e9a8e6291dea962..261b2edd10b18f5935d0b9325b6493d487ae7f4a 100644
--- a/gpu/command_buffer/service/buffer_manager.cc
+++ b/gpu/command_buffer/service/buffer_manager.cc
@@ -34,6 +34,7 @@ BufferManager::BufferManager(MemoryTracker* memory_tracker,
       allow_buffers_on_multiple_targets_(false),
       allow_fixed_attribs_(false),
       buffer_count_(0),
+      primitive_restart_fixed_index_(0),
       have_context_(true),
       use_client_side_arrays_for_stream_buffers_(
           feature_info
@@ -199,13 +200,17 @@ void Buffer::ClearCache() {
 }
 
 template <typename T>
-GLuint GetMaxValue(const void* data, GLuint offset, GLsizei count) {
+GLuint GetMaxValue(const void* data, GLuint offset, GLsizei count,
+    GLuint primitive_restart_index) {
   GLuint max_value = 0;
   const T* element =
       reinterpret_cast<const T*>(static_cast<const int8_t*>(data) + offset);
   const T* end = element + count;
   for (; element < end; ++element) {
     if (*element > max_value) {
+      if (*element == primitive_restart_index) {
+        continue;
+      }
       max_value = *element;
     }
   }
@@ -213,13 +218,53 @@ GLuint GetMaxValue(const void* data, GLuint offset, GLsizei count) {
 }
 
 bool Buffer::GetMaxValueForRange(
-    GLuint offset, GLsizei count, GLenum type, GLuint* max_value) {
-  Range range(offset, count, type);
+    GLuint offset, GLsizei count, GLenum type, bool primitive_restart_enabled,
+    GLuint* max_value) {
+  GLuint primitive_restart_index = 0;
+  if (primitive_restart_enabled) {
+    switch (type) {
+      case GL_UNSIGNED_BYTE:
+        primitive_restart_index = 0xFF;
+        break;
+      case GL_UNSIGNED_SHORT:
+        primitive_restart_index = 0xFFFF;
+        break;
+      case GL_UNSIGNED_INT:
+        primitive_restart_index = 0xFFFFFFFF;
+        break;
+      default:
+        NOTREACHED();  // should never get here by validation.
+        break;
+    }
+  }
+
+  Range range(offset, count, type, primitive_restart_enabled);
   RangeToMaxValueMap::iterator it = range_set_.find(range);
   if (it != range_set_.end()) {
     *max_value = it->second;
     return true;
   }
+  // Optimization. If:
+  //  - primitive restart is enabled
+  //  - we don't have an entry in the range set for these parameters
+  //    for the situation when primitive restart is enabled
+  //  - we do have an entry in the range set for these parameters for
+  //    the situation when primitive restart is disabled
+  //  - this entry is less than the primitive restart index
+  // Then we can repurpose this entry for the situation when primitive
+  // restart is enabled. Otherwise, we need to compute the max index
+  // from scratch.
+  if (primitive_restart_enabled) {
+    Range disabled_range(offset, count, type, false);
+    RangeToMaxValueMap::iterator it = range_set_.find(disabled_range);
+    if (it != range_set_.end() && it->second < primitive_restart_index) {
+      // This reuses the max value for the case where primitive
+      // restart is enabled.
+      range_set_.insert(std::make_pair(range, it->second));
+      *max_value = it->second;
+      return true;
+    }
+  }
 
   uint32_t size;
   if (!SafeMultiplyUint32(
@@ -243,21 +288,24 @@ bool Buffer::GetMaxValueForRange(
   GLuint max_v = 0;
   switch (type) {
     case GL_UNSIGNED_BYTE:
-      max_v = GetMaxValue<uint8_t>(shadow_.get(), offset, count);
+      max_v = GetMaxValue<uint8_t>(shadow_.get(), offset, count,
+          primitive_restart_index);
       break;
     case GL_UNSIGNED_SHORT:
       // Check we are not accessing an odd byte for a 2 byte value.
       if ((offset & 1) != 0) {
         return false;
       }
-      max_v = GetMaxValue<uint16_t>(shadow_.get(), offset, count);
+      max_v = GetMaxValue<uint16_t>(shadow_.get(), offset, count,
+          primitive_restart_index);
       break;
     case GL_UNSIGNED_INT:
       // Check we are not accessing a non aligned address for a 4 byte value.
       if ((offset & 3) != 0) {
         return false;
       }
-      max_v = GetMaxValue<uint32_t>(shadow_.get(), offset, count);
+      max_v = GetMaxValue<uint32_t>(shadow_.get(), offset, count,
+          primitive_restart_index);
       break;
     default:
       NOTREACHED();  // should never get here by validation.
@@ -536,6 +584,28 @@ Buffer* BufferManager::GetBufferInfoForTarget(
   }
 }
 
+void BufferManager::SetPrimitiveRestartFixedIndexIfNecessary(GLenum type) {
+  GLuint index = 0;
+  switch (type) {
+    case GL_UNSIGNED_BYTE:
+      index = 0xFF;
+      break;
+    case GL_UNSIGNED_SHORT:
+      index = 0xFFFF;
+      break;
+    case GL_UNSIGNED_INT:
+      index = 0xFFFFFFFF;
+      break;
+    default:
+      NOTREACHED();  // should never get here by validation.
+      break;
+  }
+  if (primitive_restart_fixed_index_ != index) {
+    glPrimitiveRestartIndex(index);
+    primitive_restart_fixed_index_ = index;
+  }
+}
+
 bool BufferManager::OnMemoryDump(const base::trace_event::MemoryDumpArgs& args,
                                  base::trace_event::ProcessMemoryDump* pmd) {
   const int client_id = memory_tracker_->ClientId();