[RFC xserver 1/1] xwayland: reduce over-damage

[Daniel Stone]

 Hi Pekka,

On 20 December 2017 at 11:18, Pekka Paalanen <ppaalanen at gmail.com> wrote:
> If an X11 app draws a little here, some there, and a tiny bit in the
> opposite corner, using RegionExtents for the damage to be sent to the
> Wayland compositor will cause massive over-damaging.
>
> However, we cannot blindly send an arbitrary number of damage
> rectangles, because there is a risk of overflowing the Wayland
> connection. If that happens, it triggers an abort in libwayland-client.
>
> Try to be more accurate with the damage by sending up to 500 rectangles
> per window, and fall back to extents otherwise. The number is completely
> arbitrary.

I might have said this on IRC, but 500 sails close enough to our
request limit for comfort. I can't find the mail where I did the
maths, but ISTR for damage requests, it's around the 6000-7000 mark.
Pulling 256 as an equally arbitrary number out of the air (arguably
even that number of TexSubImage requests represents a DoS), this is:
Reviewed-by: Daniel Stone <daniels at collabora.com>

Cheers,
Daniel