[Kstars-devel] Some research about drawing speed

[Khudyakov Alexey]

Oops finger slipped...

At some point I slow sky drawing really annoyed me. In development version 
full sky redraw take ~1s. And I profiled code with valgrind. Here some results. 

Profiling shown that ~75% of time is spent in QPainter::draw* routines. It's on 
one hand is good result which means that our code is decently fast. On other 
hand it means that there is no easy way to optimise it. 

After some googling I found that Qt4.5 included new feature. It has different 
paint engines. Native/raster/opengl. Both raster and opengl engines outperform 
native. However there isn't much info about it so I can be mistaken at some 
point. 

Only infomative links I've found. 
http://doc.trolltech.com/4.5/qpaintengine.html

Engine could be chosen with: 
$ path/to/kstars -graphicssystem {raster,opengl}
With raster I've got approximately 5x speed increase and kstars became 
responsive. 
With opengl - immediate crash. 



Another curious thing I've found. When Ctrl key pressed forceUpdate event in 
SkyMap is somehow toggled. I believe it's a bug. Should investigate it 
further.

--
  Khudyakov Alexey