[PATCH weston] gl-renderer: compress pixman bands to simplify geometry

[Jasper St. Pierre]

On Wed, Nov 19, 2014 at 7:22 AM, Daniel Stone <daniel at fooishbar.org> wrote:

> Hi,
>
> 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
> it.
>
> 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. [0]

[0] Or steal
http://cgit.freedesktop.org/plymouth/tree/src/libply/ply-region.c


> Cheers,
> Dan
>
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>


-- 
  Jasper
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