[wayland] some findings about weird shadows in wayland

[Marco Martin]

Hi all,
since i don't have much time to look in it the next few days, i'm dumping here 
some interesting findings i did on an issue i'm having on kwin/wayland (qt 5.9)
I'll continue to look into that, but if this immediately rings a bell to 
someone, even better.

Sometimes shadows (especially of plasma tooltips and sometimes QMenu submenus) 
are wrong, usually a bit taller than the window is.

putting some debug around, i see in kwin, shadow.cpp geometrychanged() i see 
m_toplevel having indeed the wrong geometry (few pixels too tall, the same 
anount the graphical artifact is) while if i put debug statements on every 
resize event of the same plasma tooltip, it never gets resized to that size, 
but always stays less tall.

if really some times the geometry of a toplevel in kwin is not the real one, 
that's indeed a problem that could explain other potential bugs other than the 
artifact often appearing for shadows

-- 
Marco Martin