[Kstars-devel] KStars & OpenGL

[Henry de Valence]

I've been trying to work out a way for KStars to be able to do both GL and 
non-GL painting. The problem is that in order to paint using GL, one must use 
a QGLWidget, but in order to paint using a normal QPainter (i.e., without GL), 
one needs to use a QWidget. Currently the SkyMap class inherits QWidget and 
uses that to paint. We can't make classes that inherit from SkyMap and one of 
(QWidget, QGLWidget), because SkyMap would still have to inherit QObject to 
get signals and slots, and multiple inheritance of QObject is not allowed. 
I've been working at separating all of the SkyMap code that is dependent on 
the inheritance from QWidget into another class for the past week, and even 
though the diff is so far over 2000 lines, I'm not even close to getting it to 
work, and it doesn't seem likely that I will be able to get it to work, at 
least within the time that I have -- since I have to actually implement GL 
painting, not just refactor things.

When I was talking to Akarsh about this, he suggested the following:
1. We use OpenGL as the only rendering engine.
2. When dealing with "non-3D" graphics cards which don't have hardware support 
for fancy stuff, we cut down on effects and use OpenGL just as we'd use 
QPainter.

One way to implement #2 would be to have KStars monitor its frame rate, and 
then automatically adjust the graphics quality so that it fell within a 
certain range (say, minimum 10 FPS, maximum 30 FPS): if the frame rate is too 
low, it would disable certain effects, and if the frame rate is too high, it 
would enable more expensive effects. Since I plan on putting drawing methods 
into a helper class (so that the drawing code is all in one place), it should 
be possible to have that helper class manage the level of graphical effects, 
taking into account performance and graphics card features.

Does this seem like a reasonable approach?

Henry de Valence