Zhenyao and Ken, I have one question about clear the uncleared texture. 

As you know, on command buffer service side, we have a class TextureManager to manage the texture related information. In TextureManager, we have complicated code to set/get the cleared rect for a particular mipmap level for 2D texture. 
But for 3D texture, we just simply clear the entire texture. So I wonder do we also need to upgrade the code to clear a small rect for a specific level/layer for 3D texture? In this CL: https://codereview.chromium.org/2208733002/. I tried to follow the design and add LayerInfo to LevelInfo to clear a small rect for a specific layer of a mipmap level for 3D texture. 
But I am not sure whether this logic is necessary. 
Why it is necessary for 2D/3D texture to clear a small rect? For instance, If a specific level of the texture is 4*4, and we only read a 2*2 rect from fbo by CopyTex{Sub}Image2D to the texture, then we just clear the 2*2 rect. If we read another 2*2 next to the previous rect, we will clear this 2*2 rect, and combine the cleared rect to 2*4. why don't we clear the entire mipmap level (4*4) at the first time, and don't need to care about the cleared rect in following operations? In addition, we don't need so many complicated code to manage the cleared rect.
 
I guess that we can initialize as small part as possible for texture. So we can upload a small bunch of data and save the memory bandwidth and improve the perf for some cases. If this is true, should we clear a small part only for 3D texture, instead of clearing the entire 3D texture? You know, a 3D texture may be very big, need to upload lots of data (zeros).

Any comments?

I misunderstand the code in Chromium. Close this issue.