On 05/29/2013 12:31 AM, Alexander Larsson wrote:
I don't think you can avoid non-integer scaling. What happens if a
client says it's scale is 3 and the output has a scale of 2? This is not
just hypothetical, it will certainly happen if there is both a scale 3
and scale 2 output on the device.
Yes, the actual scaling that the compositor has to apply from the buffer
to a given output may be fractional. However, the scaling factor between
the buffer and the surface (i.e. in pels or in global compositor
relative sizes) is an integer. This means that any integer position in
surface space corresponds to an integer in buffer space, so for instance
a pixman region (in ints) damage or clip region in surface space
corresponds to an exact pixman region in buffer coordinates. And, this
is the transformation that the compositor really cares about internally
(e.g. for input scaling, clipping, dirty tracking, etc) rather than the
final drawing translation.
The compositor will produce regions that are not integers in surface
space. For instance the damage from an overlapping window atop a surface
who's scale is not an integer will produce a region that is fractional
in that lower surface's space.
I agree that the compositor will then immediately expand these to
integer buffer coordinates, but I don't think limiting the scales to
integers is buying you anything.
The client should send regions to the compositor in buffer pixels. It
has to use these coordinates to draw and things like "opaque region" are
much more related to drawing than anything else.
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