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

[Pekka Paalanen]

On Wed, 19 Nov 2014 09:03:31 -0800
"Jasper St. Pierre" <jstpierre at mecheye.net> wrote:

> 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

$ git grep -E 'pixman_region.._.+\(' | egrep -o 'pixman_region.._.+\(' | sort | uniq -c | sort -n
      1 pixman_region32_contains_point (
      1 pixman_region32_equal(
      1 pixman_region32_init_rects(
      1 pixman_region32_translate(&final_region, (int)view_x, (
      3 pixman_region32_init_with_extents(
      3 pixman_region32_intersect_rect(
      8 pixman_region32_clear(
     10 pixman_region32_contains_point(
     12 pixman_region32_translate(
     14 pixman_region32_intersect(
     15 pixman_region32_extents(
     15 pixman_region32_rectangles(
     15 pixman_region32_union(
     15 pixman_region32_union_rect(
     17 pixman_region32_not_empty(
     23 pixman_region32_subtract(
     25 pixman_region32_copy(
     26 pixman_region32_init_rect(
     63 pixman_region32_init(
     88 pixman_region32_fini(

We even have wl_region.subtract in the core protocol, so union only is
not enough.


Thanks,
pq