surface buffer cardinality and outputs

[Bill Spitzak]

Pekka Paalanen wrote:

> I always tend to assume we do not communicate the matrix, since that
> exposes the global or output coordinate system, and surface
> positions.

The transform is between the 0,0,w,h rectangle that the client claims 
the surface occupies and the contents of the buffer. It does not include 
where the surface is on the outputs.