sky rendering

[alex25]

i don't really now what i am doing, so bear with me. i am trying to understand how the drawing of the sky works, so i started reading the code. in src/graphics.cpp around line 1396 we have the following code:

Code:

if (i->GetDraw()->skybox)
                        {
                                glPushMatrix();
                                double temp_matrix[16];
                                game.cam.PutTransformInto(temp_matrix);
                                glLoadMatrixd(temp_matrix);
                                if (game.track.GetVerticalTrackingSkyboxes())
                                {
                                       glTranslatef(0,game.cam.position.y,0);
                                 }
                                glMultMatrixf(i->GetMatrix4()->data);
                        }

this does the vertical tracking for the skyboxes. because i don't know what i am doing (and looking at the values of cam.position.y and object_center_y), i changed glTranslatef(0,game.cam.position.y,0) to glTranslatef(0,-objpos.y,0) where objpos is the y position of the skybox center:

Code:

VERTEX objpos(i->GetDraw()->object_center);
        objpos = i->GetDraw()->parent->TransformIntoWorldSpace(objpos);

and suddenly the horizon at imola and nurburgring and suzuka and barcelona and melbourne (and all the other rFactor based tracks i've been playing with) started getting drawn correctly (or at least what i think it should look like). the sky didn't look too good if it was just a dome (presumably because the object center was way up and the sky got pulled in) but that's a minor inconvenience (and it can be addressed by having a separate sky and horizon type). for the racer and gpl (grand prix legends that is) tracks one would need to disable vertical tracking (because the horizon in that case is a cylinder or dome encompassing the whole track of very large size).

so, based on the above, can somebody who knows more about openGL explain to me why this wouldn't be the transformation we want to apply to the horizon? thanks.

hope i made myself clear.

--alex--