Problem with rendering single-sided faces

Support Basics & Interface
#1

Hi!

I’m trying to create objects with single-sided faces. I’d like for the single-sided faces not to be rendered when seen from the “back”. It would also be nice if the “backs” of faces were invisible in edit/object mode.

I’m trying to get this working with a cube at the moment. I’ve created a cube and removed the top face, to leave an open box. Then I’ve switched off “Double Sided” in the Mesh options. I’m also viewing normals, so I can be sure all the normals are facing outwards.

Looking inside the box at the “back” of some faces, they are still being drawn (albeit darker) in object and edit mode, and they seem to be appearing as double-sided faces when I render the object. :expressionless:

I’m sorry if this a common question - I’ve done a lot of searching both on these forums and on Google.

Can anyone help?

#2

There are no single sided faces in blender (well - there are in the game engine). There is a nice trick to fake single sided faces. Straight from the manual:
http://mediawiki.blender.org/index.php/Manual/PartIV/Map_Input
And you may leave double sided on.

#3

Thanks for that, soylent_gr. That link looks like it’ll solve my problem :slight_smile:

I’m interested, though: are there any benefits with making everything double-sided by default?

I’m no expert (been 3d modelling for exactly 1 week!) but I’ve been told other 3d apps create single faces by default as this produces the lowest number of polys and smallest overhead… And if single sided is possible/necessary in the game engine, why not the rest of Blender?

Regards…

#4

I don’t think single sided faces would be beneficiall. If you can’t see them, the rendering algorithm will not render them at all. But if you would look on a single sided face (like a plane, just something you need to carry a texture), and could not see it, this would be really strange.

As far as I can tell, the option “Double sided” has no effect whatsoever to the rendered image (but “No vertex normal flip” has). If I remember correctly, there has been an issue with mirrored meshes, but I think that has been fixed a long time ago.

#5

'sa fair point. Double-sided makes shapes in blender fit real-life conceptual models, and the link you pointed to shows faking single-sided is quite do-able.

Thanks for your thoughts :slight_smile:

#6

For information on faking single sided faces go here:

http://wiki.blender.org/index.php/Tutorials/Textures/Map_Input_Techniques

Basically you map a black and white ramp to the normal input and connect that up to the alpha making sure the input is taking the z and negating the next two. I’m just leaving this as a note just in case the link I’m updating goes stale as well so who ever finds this will at least have a place to start.