View Full Version : Double sided polygons in Max...

11 November 2005, 08:04 PM
Can anyone tell me how to make it so a polygon will render from both sides in Max? The normals point out on one side, so if its "back" is facing the camera it won't render. I am doing a tree and the big square polys that make up the branches don't render well. Any help would be oh so appreciated :)

11 November 2005, 08:23 PM
the easiest way would be to apply a 2 sided material

in your material editor just turn on 2 sided

Wayne Adams
11 November 2005, 08:25 PM
or you can right click the object and under properties turn OFF backface cull.
to see it in a render under render options check force 2 sided.

11 November 2005, 09:07 PM
Thank you guys so much! :) Now I have a different problem. Some of the branches are too dark because the back side is shaded (See Tree3). Any way around this?

11 November 2005, 08:45 AM
What you really want to do is duplicate and flip the face. If you use a 2-sided material, or turn off back face culling, and your game engine supports it (many won't), then what you'll of done is effectively doubled your polygon count, because the object can either be all 2 sided, or all single sided.

If you try to skip around this issue with using 2 shaders, or splitting your object in two, so you can have some parts in single sided, and some parts in double, the game engine will likely not be able to compress these into a single mesh, and it will export as two meshes, giving you 2 render calls. This is similar to the cost your model would have if there were 2 of them in the scene.

Best bet, is to take the offending polygons, duplicate then flip them.

I find in our engine, it works out fine if you merge the verts together (thus giving you an object with the same number of verts you had before, but with 2 sides), but what you have to do is put an edit normal modifier on, and manually split the normals so that each side doesn't get shading errors.

Wayne Adams
11 November 2005, 01:51 PM
Dargon: I did not know that. I use DBPro for my engine (don't ask ;)), and I never really noticed the effect that doing that had. (DBPro supports non culled faces.) So you clone the plane flip it with mirror or whatever. then merge the verts? Is that collapsing them or welding them together? That actually works? Damn when I get home I'm gonna try that. Crazy times....crazy times...

11 November 2005, 02:00 PM
hey there is a way of getting rid of those dark light shading artefacts.

1 use more polys and more spread out leaves with more space in between. (probably not what you want)

2 edit the normals so that they all point upwards, this means you get that soft look.

CGTalk Moderation
11 November 2005, 02:00 PM
This thread has been automatically closed as it remained inactive for 12 months. If you wish to continue the discussion, please create a new thread in the appropriate forum.