Unlike OpenGL ES 2.0, 3.0 allows framebuffer attachments to be of
different sizes: "If the attachment sizes are not all identical, the
results of rendering are defined only within the largest area that
can fit in all of the attachments. This area is defined as the
intersection of rectangles having a lower left of (0, 0) and an upper
right of (width, height) for each attachment. Contents of attachments
outside this area are undefined after execution of a rendering command
(as defined in section 2.6)."

Change-Id: Ib75be93650edd7d6a7f3d08d9206830094e3fbd8
Reviewed-on: https://swiftshader-review.googlesource.com/15469Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>