LDraw.org Discussion Forums

Full Version: Question on faces
You're currently viewing a stripped down version of our content. View the full version with proper formatting.
Pages: 1 2
Hi, i have a question: are faces considered double sided in parts that are not "BFC certified"?
For example i'm rendering part 6595 and it renders wrong, it's not certified as far as i can see.
triangles and quads which are not BFC-enabled (e.g. in non-certified files, or in a section of a file enclosed in
0 BFC NOCLIP
...
0 BFC CLIP
must be treated non-oriented, i.e., it cannot be derived an "inside" and "outside" facing surface of them.
They must be rendered from whatever side you look at them.
In OpenGL as far as I remember, there's a global rendering option by which you can turn on and off the logic
if to render such a surface or not. I don't think that you can turn and off it for individual quads or triangles, though.

Thus, the only solution that comes to my mind is: if you encounter such data, you will probably be forced to turn off
the CW/CCW optimization logic of your OpenGL renderer for the _whole_ scene...
Quote:Thus, the only solution that comes to my mind is: if you encounter such data, you will probably be forced to turn off
the CW/CCW optimization logic of your OpenGL renderer for the _whole_ scene...
Or use two overlapping but opposite winding elements? BCFed parts are more and more frequent nowadays...
yes, that's of course a MUCH better solution
In OpenGL, there are two settings to get the "back" side of faces to render. Two-sided lighting must be enabled if using OpenGL's lighting, and GL_CULL_FACE must be disabled. LDView does this for non-BFC geometry. However, Philo's suggestion of drawing the triangle twice with opposite windings is probably a better solution, and if I were doing things over again, that's probably what I would do.
yes, thanks, i'll go with this solution
Another thing, i've found that some parts in standard library (ie 6595a.dat) have quads in an "hourglass" configuration, not ccw or cw. As stated here it's a bad configuration. Have i stumbled on a broken part or should i implement some kind of quad correction software? IIRC LDView render it correctly.
You may indeed encounter such quads ("bow-tie" in LDraw jargon) in old, non-BFCed files. You must indeed provide some correction if you want to display them correctly Sad
Ok... I'm almost afraid to ask but: what if one wants to correct the part? after all is just switching a couple of vertices.
What's the iter to correct a part ?
Hi Nicola , I love your web rendering tool.

I made a quick review of that part, 6595.dat, and indeed, it badly needs some corrections.
All files, main and sub-files, are missing a bfc-statement.
All quads, in all four sub-files, are bowtie-quads.
All sub-files are missing many of the needed cond-lines.

Correcting bfc is easy with DatHeader, and the missing cond-lines could be made with Edger2.
It should also be renamed to follow the new nomenclature for wheel rims.

If you wanna have a go at it, correct all files and send them to Admin
but I think that you first have to register as an author.

If not, let me know, and I'll do it.
Pages: 1 2