[gl2ps] Plot-application for gCAD3D

[Franz Reiter]

Hallo

your software gl2ps is very impressive. I am working on a similar problem
 and so i would like to ask you about the following OpenGL-problem:

I want to produce a plot of an OpenGL-3D-Object.
The plot shall consist only of 2D-Lines of the visible edges of
 the OpenGL-object (all hidden lines removed).
 No colours and textures are wanted (this shall also be a tool for
 3D to 2D drawing-conversion).

The OpenGL-3D-Object consists of GL_LINES, GL_LINE_STRIP, GL_POLYGON;
 (rendered triangles).

What i have done till now:
  i can produce a OpenGl-Image with hidden lines removed; OK
  (i do this by using glStencilFunc - like demoprog hiddenline.c)
  afterwards i read the result with GL_FEEDBACK; but the feedback-buffer
  always provides all lines (even the hidden lines).
MY PROBLEM: how can i get only the visible lines ?

This function would be very useful for gCAD3D; a Freeware - CAD-program;
http://www.cadcam.co.at/freiter/gCAD3D.htm

Thank you for your time and for any information

greetings from Vienna

Franz Reiter.