[PATCH weston] gl-renderer: compress pixman bands to simplify geometry
Jasper St. Pierre
jstpierre at mecheye.net
Wed Nov 19 09:03:31 PST 2014
On Wed, Nov 19, 2014 at 7:22 AM, Daniel Stone <daniel at fooishbar.org> wrote:
> On 19 November 2014 14:58, Derek Foreman <derekf at osg.samsung.com> wrote:
>> Since we're sort of on the topic, is there anywhere we gain anything
>> from y-x banded regions? I'm wondering if it would be worthwhile to
>> replace pixman's region code with something that doesn't band. I think
>> this would let us drop the pixman dependency when not building the
>> pixman renderer...
> Not really, no. Pixman only does it because the X server requires regions
> to be marked as YX-banded to be deigned valid (or 'complete', as an FBO
> analogy), and a number of the rendering algorithms in the server depend on
> We don't have any of that, so can happily do without banding. A patch to
> Pixman which would optionally drop the strict banding would be nice, but if
> there's a small enough region implementation we could use instead, that
> could work.
It's more that the algorithms for combining regions only work in the case
where you have a vertically-sorted list of horizontal bands. So, you would
have to come up with an entirely new algorithm for pixman_region_union,
pixman_region_subtract, etc. if want some other format.
What's the format you're suggesting? If we flip the axes (horizontally
sorted list of vertical bands), then it will work fine for the move up/down
case, but break for the left/right case.
Derek's approach of post-processing the bands to make a minimal set of
overall rectangles seems fine to me.
If we only need union, then we could very simply create our own region
class that did what we wanted. 
 Or steal
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