[gl2ps] Depth issues in GL2PS

[Christophe Geuzaine]

Hmm, weird. I would start by debugging what's actually in the feedback buffer (gl2psParseFeedbackBuffer) and see if the error is already there.


On 12 Oct 2012, at 23:23, David Lonie <david.lonie at kitware.com> wrote:

> Hi list,
> 
> I'm using GL2PS to export a scene that is drawn in 2D, e.g. at
> constant Z in OpenGL.
> 
> I've verified that z is the same for all vertices in the feedback
> buffer by watching gl2psGetVertex. In all cases, p[2] = 0.5.
> 
> However, by the time the primitives are sorted, some of the vertices
> are at different depths. Most are at 0.0, but a few are at -20.0.
> 
> This wasn't an issue for pure 2D scenes -- I just turned off sorting,
> and the primitives were rendered in painter order and everything
> worked great. Now we're trying to mix 2D painter rendering with 3D
> geometry, so we need to sort these guys, and the z=-20 vertices are
> throwing off the renderings.
> 
> Any idea why some vertices are being transformed differently? I don't
> mind debugging/fixing this, but I'd greatly appreciate some pointers
> to likely culprits in the code.
> 
> Somewhat related: I've had to add a stable sorting method to preserve
> the painter order for the 2D primitives. I'll send a patch for this
> once I get this other issue sorted out.
> 
> Thanks in advance,
> 
> Dave
> 
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-- 
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science 
http://www.montefiore.ulg.ac.be/~geuzaine