gpu: Allow BufferData size=0 for pixel transfer buffer objects.

This makes it possible to release all shared memory used by a
pixel transfer buffer without destroying the Id.

BUG=163482
TEST=manual


Review URL: https://chromiumcodereview.appspot.com/11415223

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@170776 0039d316-1c4b-4281-b951-d872f2087c98

gpu/command_buffer/client/buffer_tracker.cc

@@ -24,12 +24,15 @@ BufferTracker::~BufferTracker() {
 BufferTracker::Buffer* BufferTracker::CreateBuffer(
     GLuint id, GLsizeiptr size) {
   GPU_DCHECK_NE(0u, id);
-  GPU_DCHECK_LT(0, size);
-  int32 shm_id;
-  uint32 shm_offset;
-  void* address = mapped_memory_->Alloc(size, &shm_id, &shm_offset);
-  if (!address) {
-    return NULL;
+  GPU_DCHECK_LE(0, size);
+  int32 shm_id = -1;
+  uint32 shm_offset = 0;
+  void* address = NULL;
+  if (size) {
+    address = mapped_memory_->Alloc(size, &shm_id, &shm_offset);
+    if (!address) {
+      return NULL;
+    }
   }
 
   Buffer* buffer = new Buffer(id, size, shm_id, shm_offset, address);
@@ -56,8 +59,8 @@ void BufferTracker::RemoveBuffer(GLuint client_id) {
 }
 
 void BufferTracker::FreePendingToken(Buffer* buffer, int32 token) {
-  GPU_DCHECK(buffer->address_);
-  mapped_memory_->FreePendingToken(buffer->address_, token);
+  if (buffer->address_)
+    mapped_memory_->FreePendingToken(buffer->address_, token);
   buffer->size_ = 0;
   buffer->shm_id_ = 0;
   buffer->shm_offset_ = 0;

gpu/command_buffer/client/buffer_tracker_unittest.cc

@@ -70,5 +70,19 @@ TEST_F(BufferTrackerTest, Basic) {
   EXPECT_TRUE(buffer_tracker_->GetBuffer(kId1) == NULL);
 }
 
+TEST_F(BufferTrackerTest, ZeroSize) {
+  const GLuint kId = 123;
+
+  // Check we can create a Buffer with zero size.
+  BufferTracker::Buffer* buffer = buffer_tracker_->CreateBuffer(kId, 0);
+  ASSERT_TRUE(buffer != NULL);
+  // Check mapped memory address.
+  EXPECT_TRUE(buffer->address() == NULL);
+  // Check no shared memory was allocated.
+  EXPECT_EQ(0lu, mapped_memory_->num_chunks());
+  // Check we can delete the buffer.
+  buffer_tracker_->RemoveBuffer(kId);
+}
+
 }  // namespace gles2
 }  // namespace gpu

gpu/command_buffer/client/gles2_implementation.cc

@@ -1191,10 +1191,6 @@ void GLES2Implementation::ShaderSource(
 
 void GLES2Implementation::BufferDataHelper(
     GLenum target, GLsizeiptr size, const void* data, GLenum usage) {
-  if (size == 0) {
-    return;
-  }
-
   if (size < 0) {
     SetGLError(GL_INVALID_VALUE, "glBufferData", "size < 0");
     return;
@@ -1224,6 +1220,10 @@ void GLES2Implementation::BufferDataHelper(
     return;
   }
 
+  if (size == 0) {
+    return;
+  }
+
   // If there is no data just send BufferData
   if (!data) {
     helper_->BufferData(target, size, 0, 0, usage);