[Kstars-devel] OpenGL: the beginning

[Jason Harris]

Hello,

I have started an OpenGL framework that I plan to evolve into a 
replacement for our SkyMap widget.  Actually, my plan is to include 
both SkyMap and SkyMapGL, and let configure determine which should be 
used.

I'm just getting started, but I thought I'd share with you what I have 
so far.  Get the tarball here:

http://www.30doradus.org/kstars/kglbasic-0.1.tar.gz

Do './configure' and 'make'; there's no need to do 'make install'.  The 
class KGLWidget is what will eventually be SkyMapGL; KGLWindow is just 
a KMainWindow container.  

Right now, it just displays the coordinate grid, and you can scroll with 
the arrow keys and zoom in/out with the +/- keys.  It seems really 
smooth on my system, but I have hardware acceleration, so I don't know 
how software openGL compares yet.

OpenGL will require some fundamental changes in how we represent objects 
in the sky.  The paradigm is that you create objects in a cartesian 3D 
volume (with X,Y,Z coordinates) and then define a "camera" for 
projecting those objects into the 2D window.  

For KStars, this means that each object's RA/Dec coordinates will be 
converted to X,Y,Z such that each lies on the surface of a "celestial 
sphere" in the 3D volume.  Once this is done, everything gets much 
simpler compared to our current setup.  For example, rather than 
recalculating every object's pixel coordinates whenever the Focus 
position is changed, we simply tell OpenGL that the camera has moved, 
and it computes a matrix transformation internally and re-renders the 
scene.  Also, things like Precession and Nutation can be simplified as 
rotational matrix transformations of the fundamental J2000 Celestial 
sphere.  We don't even need to determine if each object is visible on 
the screen; we just define a "clipping volume", and OpenGL takes care 
of it (say goodbye to checkVisibility()!).  The only calculations we'll 
need to do as a function of time are updating the (X,Y,Z) coordinates 
of solar system bodies, and of nearby stars (if/when we include proper 
motions).  Pretty cool.

The KGLWidget::makeObject() function will eventually be where we define 
the XYZ coordinates of our objects and how to render them.  This 
function was copied frm the Qt OpenGL "box" example, but it is not 
currently used in kglbasic.  Instead, the coordinate grid is defined 
with the glutWireSphere() function.

Anyway, let me know what you think.

regards, and Happy Thanksgiving
Jason

-- 
KStars: A KDE Planetarium
http://edu.kde.org/kstars