Show backfaces

Unity Engine
1

Is unity able to show backfaces? In other words, if I have an open box that has no thickness, can I see both the inside of the box and the outside?

So far I can’t se how to turn this on. I did a search and can’t find info on this, and I see no button for it…

Thanks.

2

Actually there’s a million topics on this; do a search on “two-sided” or similar.

–Eric

3

Ok, so I guess the answer is “no, you can’t do that”

4

Totally possible and asked/answered many times. Getting a decent FAQ up and running is my New Year resolution :wink:

http://forum.unity3d.com/viewtopic.php?t=14134
http://forum.unity3d.com/viewtopic.php?t=16124&sid=94f615c74126ea240b8d7c2a129a7a7c
http://forum.unity3d.com/viewtopic.php?t=709
http://forum.unity3d.com/viewtopic.php?t=10734&view=next&sid=52e485ccff7d28a37671283c2c1bfa6c
http://forum.unity3d.com/viewtopic.php?p=89319&highlight=&sid=6f931d50759f206842161b7dfcd3061c
http://forum.unity3d.com/viewtopic.php?t=9549
http://forum.unity3d.com/viewtopic.php?t=2376
http://forum.unity3d.com/viewtopic.php?p=79494&highlight=&sid=ebfc53bd0cee91db0b3b226e8868c2c0
http://forum.unity3d.com/viewtopic.php?t=14084
http://forum.unity3d.com/viewtopic.php?t=7765
http://forum.unity3d.com/viewtopic.php?p=66006

Cheers,
Ethan

5

Ok, thanks, but I think the answer is still that you can’t show backfaces, all the solutions involve making more polygons with flipped normals, not actually seeing the back-faces of the same polygons, correct?

In director (admittedly a far inferior system) you could just toggle “show backfaces” for any given material, that’s why I thought it might be a feature in Unity.

As for the searching, my original problem with the search function is that I got tons of results that had nothing to do with backfaces.

6

In any shader in Unity you can turn backface culling off. However to get correct lighting it is preferable to duplicate the faces and invert the normals… please read through the links again for more thorough explanations of both cases.

Immediately assuming that something isn’t possible when starting to learn a new tool seems like an unproductive attitude :wink:

Ethan

7

When you check the shader code, you notice a command that says Cull on… Make this Cull off and save the shader under a different name… thats the whole trick. An object using that shader is excluded from backface culling and though you can see its polygons from both sides…

8

I agree it’s not a productive attitude, but to be fair, “totally possible” may not be the most spot-on comment when it’s not actually possible to enable seeing back-faces with correct lighting without creating additional polys.

(This is according to what I’ve read; please correct me if it’s wrong.)

Rune

9

I think any solution that does correct lighting on two sided polygons will have to duplicate the polygons somehow. Yes, in Unity you have to do that manually. Yes, maybe it would be more convenient if it was done by Unity behind the scenes. But the end result is that the polygons will be duplicated either way (*).

(*) I think it’s possible to write custom vertex shaders that compute double sided lighting without duplicating polygons. E.g. date dot(light,normal), and make it always be positive. Or something like that. But this requires custom shaders.

10

Sure, all I meant was that even if it’s a reasonable and normal limitation that is there for a good reason, it still makes little sense to make it sound like the limitation isn’t there.

Well, custom shaders isn’t normally a problem in Unity, right? :slight_smile: (Except on the iPhone) Disabling culling of the backfaces requires custom shaders in the first place.

I don’t know much about shaders yet, so correct me if I’m not making sense. I could see that such a shader that does correct lighting from both sides might be more expensive than shaders that don’t. In that’s the case, it makes good sense that this isn’t default. On the other hand, if it isn’t any more expensive, is there any reason for it not to be default? I mean, when would you ever want to have backfaces shown, but with incorrect lighting?

Rune

11

Hey thanks for the very detailed answers. Now I understand that it is possible to do through the shaders.

I wasn’t assuming anything, that’s why I’m asking questions.