[visionegg] map singratings on cylinder

Hi!
I would like to project singratings on a round screen, therefore I need to correct the distortion in such a way that the grating-bars have the same width everywhere. I tried to map singratings on a cylinder, but somehow the projections don't work. singrating3d doesn't work at all (is this class not supported anymore? I didn't find it in the visionegg library reference), and for singrating2d I didn't find out how to do it. I tried to change vertex coordinates in the gratings class, and I also tried to work with projections, but neither worked.
Unfortunately, I can't use the spheregrating class, since (1) I need colors, and (2) I need the projection the other way round (at the sides of the screen, the grating has to be narrower than in the center). The mapping function for the horizontal coordinates should be x'=R*tan(x/R), where R is the radius of the screen, x is the position where the ray would hit a flat screen and x' is the horizontal coordinate on the screen. 

Any idea how I could manage this?

Thanks, Kaspar

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