Implement client side PBOs for glReadPixel

gpu/command_buffer/client/gles2_implementation.cc

Index: gpu/command_buffer/client/gles2_implementation.cc
diff --git a/gpu/command_buffer/client/gles2_implementation.cc b/gpu/command_buffer/client/gles2_implementation.cc
index 0da78bcf19e1b95aa67024383ddda891e37e9eb4..1d797d8519aa0bc49cf3e25ab4dda564d7856875 100644
--- a/gpu/command_buffer/client/gles2_implementation.cc
+++ b/gpu/command_buffer/client/gles2_implementation.cc
@@ -2103,6 +2103,25 @@ void GLES2Implementation::ReadPixels(
     SetGLError(GL_INVALID_VALUE, "glReadPixels", "size too large.");
     return;
   }
+
+  if (bound_pixel_unpack_transfer_buffer_id_) {

[greggman, 2013/03/19 20:54:11]

As pointed out else where, "unpack" is for providing data to GL, "pack" is for
reading data.

[hubbe, 2013/03/19 22:42:42]

Done.

+    GLuint offset = ToGLuint(pixels);
+    BufferTracker::Buffer* buffer = GetBoundPixelUnpackTransferBufferIfValid(
+        "glReadPixels", offset, temp_size);
+    if (buffer) {
+      helper_->ReadPixels(xoffset, yoffset, width, height, format, type,
+                          buffer->shm_id(), buffer->shm_offset(),
+                          0, 0);
+      buffer->set_transfer_ready_token(helper_->InsertToken());
+    }
+    return;

[apatrick_chromium, 2013/03/19 18:34:48]

Should this not generate INVALID_OPERATION?

[hubbe, 2013/03/19 22:42:42]

Done. (And in other similar places)

+  }
+
+  if (!pixels) {
+    SetGLError(GL_INVALID_VALUE, "glReadPixels", "pixels = NULL");
+    return;
+  }
+
   // Transfer by rows.
   // The max rows we can transfer.
   while (height) {
@@ -3304,7 +3323,7 @@ void* GLES2Implementation::MapBufferCHROMIUM(GLuint target, GLenum access) {
         GL_INVALID_ENUM, "glMapBufferCHROMIUM", "invalid target");
     return NULL;
   }
-  if (access != GL_WRITE_ONLY) {
+  if (access != GL_WRITE_ONLY && access != GL_READ_ONLY) {
     SetGLError(GL_INVALID_ENUM, "glMapBufferCHROMIUM", "bad access mode");
     return NULL;
   }
@@ -3318,6 +3337,10 @@ void* GLES2Implementation::MapBufferCHROMIUM(GLuint target, GLenum access) {
     SetGLError(GL_INVALID_OPERATION, "glMapBufferCHROMIUM", "already mapped");
     return NULL;
   }
+  if (buffer->transfer_ready_token()) {

[greggman, 2013/03/19 20:54:11]

It seems like if you're going to add this check you should add it for all
operations on a buffer, not just readPixels. In other words, TexImage2D when
using a PBO should set a token and block in map if it's busy.

[hubbe, 2013/03/19 22:42:42]

I can do it either way.
I think I prefer implementing the blocking semantics as certain kinds of patters
get a lot easier this way.

+    helper_->WaitForToken(buffer->transfer_ready_token());
+    buffer->set_transfer_ready_token(0);
+  }
   buffer->set_mapped(true);
 
   GPU_DCHECK(buffer->address());