How to debug emacs repaint problems?

[joakim]

Hello,

I have a long standing problem where it appears that my build of emacs
seems to invalidate a lot of regions on screen, which leads to flicker
in my setup of vnc. 

This flicker problem doesnt appear so much in the emacs that is
installed by my distro, which is fedora, emacs 28.

It would be easier to debug this if emacs could be persuaded to give
some visual hints of which regions its invalidating. Is this possible?

I use these settings in turbovnc:
Tight+Low quality jpeg(WAN)
/opt/TurboVNC/bin/tvncconfig -set ALR=1
/opt/TurboVNC/bin/tvncconfig -set ALRAll=true

The idea is that a low quality codec should be used to refresh
invalidated rects, and then after a while be losslessly refreshed.
This works well in applications that dont invalidate the entire window,
when only small parts of the window needs to be changed.



/Joakim
-- 
Joakim Verona
joakim@verona.se