We want the guardband_x/y to be the largerst scalars such that each
viewport scaled by that amount is still a subrange of [-32767, 32767].
The old code has a couple of issues:
1) It used scissor instead of viewport_scissor, potentially taking into
account a viewport that is too small and therefore selecting a scale
that is too large.
2) Merging the viewports isn't ideal, as for example viewports with
boundaries [0,1] and [1000, 1001] would allow a guardband scale of ~30k,
while their union [0, 1001] only allows a scale of ~32.
The new code just determines the guardband per viewport and takes the minimum.
Signed-off-by: Bas Nieuwenhuizen <basni@google.com>
Acked-by: Dave Airlie <airlied@redhat.com>
Bas Nieuwenhuizen
a4c4efad89