Move vertex clipper back to single-precision floating point
intermediates. Since positions are sent down the graphics hardware as
single-precision values, this prevents useless conversions between
single and double precision values and lets compilers fit twice as
much data into vector registers. It also removes a copy by letting the
clipper store vertices directly into the vertex buffer.
This is mostly reverting the conversion to double-precision that
happened along with the switch to the weston_coord struct for vertex
coordinates (commit 10e70bf23c0a9845aa8865216763e7e29ef390f3).
Signed-off-by: Loïc Molinari <loic.molinari@gmail.com>
49053a2aa2