Only use 4-channel shaders for unpack buffers. D3D11 supports sampling other channel sizes of backing object and declaring them as 4-vectors in HLSL. This allows us to simplify the logic for fast unpack shaders significantly. Source: http://msdn.microsoft.com/en-us/library/windows/desktop/bb509700(v=vs.85).aspx (Default Values for Missing Components in a Texture) Change-Id: I7f645372f266f57bd94cdb1c795f1d30bf2a60a4 Reviewed-on: https://chromium-review.googlesource.com/181901 Reviewed-by: Geoff Lang <geofflang@chromium.org> Tested-by: Jamie Madill <jmadill@chromium.org>