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query on game engines and modelling

Submitted by ironikart on
Forum

Does you average game engine support 2 sided maps on polys? say if I were to map a single flat plane, would the texture normally only show on one side of that plane or is there a possibility of making it 2 sided?

I'm 80% sure the answer is no to this, but I need you guys to set me straight [;)]

Submitted by Pantmonger on Wed, 30/07/03 - 2:16 AMPermalink

My understanding is that most game engines can be made to 'force double sided' but its does cost in memory and run time speed. Combine this with the fact that most of the time the other side is not visable anyway and its not worth it overall. So usualy the answer is no, you just get more polys to play with instead.

Pantmonger

Submitted by rezn0r on Wed, 30/07/03 - 2:21 AMPermalink

Triangles only get drawn in one direction (clockwise, anticlockwise) unless you draw both, which is bad. Thats why when you clip through something in a game you can't see things from the inside.

Scott.

Submitted by ironikart on Wed, 30/07/03 - 5:40 AMPermalink

yeah, from my experience playing games I kinda figured that would be the case. I want to do some cloth/flag modelling in the challenge at the moment, but it's not going to look very good if the model rotates and the flag 'disappears'. I want to model it as accurate to an acceptable game model as possible... I guess this would mean if I were to do something like a flag I'd have to make a duplicate and flip the normals on it... doubling the polycount to show both sides?

Submitted by Pantmonger on Wed, 30/07/03 - 6:06 AMPermalink

" doubling the polycount to show both sides?"

Maybe more as you will need to add the edges unless you want it to vanish from the top or side.

Pantmonger

Submitted by smeg on Wed, 30/07/03 - 8:33 AMPermalink

Most engines support two-sided materials, that is to say, whether it is one or two sided is a property of the material.

The dowside to this is that the triangles share the same lighting and texturing. If a light points at the front of the flag, the back also lights up. If you point a light at the back, it will be dark on both sides.

Doubling up triangles allows accurate lighting. It also allows you to have different texture coordinates on the back of the flag, should you want to.

Long story short, you could use a two-sided max material if you choose, its your call.

Submitted by J I Styles on Sat, 16/08/03 - 12:29 AMPermalink

It's usually best to clone the faces, then just flip the normals, leaving the neighbouring verts un-welded so as not to bork vertex lighting.

Submitted by Malus on Sat, 16/08/03 - 9:21 AMPermalink

J.I. Styles: Interesting, would you possibly still have some z-buffering issues or is this a total fix?
I understand the normals are facing different directions therefore when one is drawn the other probably isn't but I haven't seen it done, I'm all curious now, hmmm.

Do you have any examples? maybe realtime ones that we could check out?

Submitted by redwyre on Sat, 16/08/03 - 9:41 AMPermalink

If the faces are flipped and exported properly, the back-faces will get culled, so there is no z-buffer issue.

Submitted by Malus on Sat, 16/08/03 - 11:04 AMPermalink

sweet, hello new technique. [:P] (old for others I'm sure)

Posted by ironikart on
Forum

Does you average game engine support 2 sided maps on polys? say if I were to map a single flat plane, would the texture normally only show on one side of that plane or is there a possibility of making it 2 sided?

I'm 80% sure the answer is no to this, but I need you guys to set me straight [;)]


Submitted by Pantmonger on Wed, 30/07/03 - 2:16 AMPermalink

My understanding is that most game engines can be made to 'force double sided' but its does cost in memory and run time speed. Combine this with the fact that most of the time the other side is not visable anyway and its not worth it overall. So usualy the answer is no, you just get more polys to play with instead.

Pantmonger

Submitted by rezn0r on Wed, 30/07/03 - 2:21 AMPermalink

Triangles only get drawn in one direction (clockwise, anticlockwise) unless you draw both, which is bad. Thats why when you clip through something in a game you can't see things from the inside.

Scott.

Submitted by ironikart on Wed, 30/07/03 - 5:40 AMPermalink

yeah, from my experience playing games I kinda figured that would be the case. I want to do some cloth/flag modelling in the challenge at the moment, but it's not going to look very good if the model rotates and the flag 'disappears'. I want to model it as accurate to an acceptable game model as possible... I guess this would mean if I were to do something like a flag I'd have to make a duplicate and flip the normals on it... doubling the polycount to show both sides?

Submitted by Pantmonger on Wed, 30/07/03 - 6:06 AMPermalink

" doubling the polycount to show both sides?"

Maybe more as you will need to add the edges unless you want it to vanish from the top or side.

Pantmonger

Submitted by smeg on Wed, 30/07/03 - 8:33 AMPermalink

Most engines support two-sided materials, that is to say, whether it is one or two sided is a property of the material.

The dowside to this is that the triangles share the same lighting and texturing. If a light points at the front of the flag, the back also lights up. If you point a light at the back, it will be dark on both sides.

Doubling up triangles allows accurate lighting. It also allows you to have different texture coordinates on the back of the flag, should you want to.

Long story short, you could use a two-sided max material if you choose, its your call.

Submitted by J I Styles on Sat, 16/08/03 - 12:29 AMPermalink

It's usually best to clone the faces, then just flip the normals, leaving the neighbouring verts un-welded so as not to bork vertex lighting.

Submitted by Malus on Sat, 16/08/03 - 9:21 AMPermalink

J.I. Styles: Interesting, would you possibly still have some z-buffering issues or is this a total fix?
I understand the normals are facing different directions therefore when one is drawn the other probably isn't but I haven't seen it done, I'm all curious now, hmmm.

Do you have any examples? maybe realtime ones that we could check out?

Submitted by redwyre on Sat, 16/08/03 - 9:41 AMPermalink

If the faces are flipped and exported properly, the back-faces will get culled, so there is no z-buffer issue.

Submitted by Malus on Sat, 16/08/03 - 11:04 AMPermalink

sweet, hello new technique. [:P] (old for others I'm sure)