Is there an efficient way to convert a3d scene to a 2d Enhanced Metafile

Question

I am developing a CAD application using Delphi2010 and OpenGL. Currently, i am working on a module to export the current view to an Image file.

This is pretty straigthforward for raster formats (render scene to offscreen Buffer of desired Dimensions, write buffer to disk), but I also wish to be able to export an axis-aligned 2d-View of my scene to a vector format, preferably Winows EMF.

I was thinking about calculating my transformations and projection in software, or misuse glFeedback functionality. Since i would have to implement my own z-buffering, this approach seems to be rather laborious, not to mention the performance issues i might face rendering a complex scene without hardware acceleration.

Since my Google-fu did not lead to a result, i want to ask if anyone of you has experience with this problem (convert Opengl-3d-scene to 2d-Vectorimage), or if there is any 3rd-party library known to implement this.

Answer 1

This is a very hard task, it involves analytical hidden lines removal, polygon splitting and Z-sorting for final output as explained here: http://www.cs.drexel.edu/~david/Classes/CS430/HWs/p214-weiler.pdf

Answer 2

There is a C library that does this. It can output PostScript, PDF and SVG. It supports smooth shading too.

While you probably won't be able to use it directly, it might give you some ideas:

http://www.geuz.org/gl2ps/