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Double sided polygons?

 
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Trullion
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Joined: 31 Mar 2010
Posts: 13

PostPosted: Thu Apr 01, 2010 4:03 pm    Post subject: Double sided polygons? Reply with quote

I am working on my first real DeleD model which is to say somethign simple...an arrow for a bow and arrow.

I have made the tip and shaft, and need to make the feathers. When I went to add in the first feather I found that you can only see the feather from one side (I used a poly line to create a simple feather shape).

How do I get it to show on both sides?
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Jeroen
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Joined: 07 Aug 2004
Posts: 5332
Location: The Netherlands

PostPosted: Thu Apr 01, 2010 4:22 pm    Post subject: Reply with quote

Indeed, polygons have only one visible side. You could extrude this polygon just a little bit to get the effect you want. So, select the object, go to Polygon mode, select the polygon, select the Extrude tool, drag in any view.

Hope this helps! Smile
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Trullion
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Joined: 31 Mar 2010
Posts: 13

PostPosted: Thu Apr 01, 2010 4:48 pm    Post subject: Reply with quote

Thanks for the info. I was afraid that was the case. Because I am trying to keep polygon counts down, I decided that instead of extruding it, to simply draw another polygon on the back side. This keeps the total polygon count for the feathers down to 6 (2 per feather) versus 18 if I extruded it.

Thanks for the help.
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harper
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Joined: 19 Jul 2007
Posts: 283
Location: Hamburg, Germany

PostPosted: Thu Apr 01, 2010 5:22 pm    Post subject: Reply with quote

But, Trullion, be careful with double-sided polys. Make a test first, if your engine is displaying both sides (called often: backface culling on/off).
If so you got annoying effects while looking at your models.
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AWM Mars
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Joined: 06 Jan 2010
Posts: 1195
Location: Wilts England

PostPosted: Thu Apr 01, 2010 8:59 pm    Post subject: Reply with quote

you could try duplicating the mesh, then mirror, then merge, all without moving the mesh.
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John
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Joined: 22 Dec 2008
Posts: 182
Location: Houston, TX

PostPosted: Thu Apr 01, 2010 9:41 pm    Post subject: Reply with quote

Yeah...stay away from them. Double sided rendering is horribly expensive.
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Jeroen
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Joined: 07 Aug 2004
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PostPosted: Fri Apr 02, 2010 7:05 am    Post subject: Reply with quote

Yep, you might experience z-buffer fighting if you have two polygons sharing the same space.
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chronozphere
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Joined: 20 Jun 2006
Posts: 1010
Location: Netherlands

PostPosted: Fri Apr 02, 2010 9:44 am    Post subject: Reply with quote

Jeroen wrote:
Yep, you might experience z-buffer fighting if you have two polygons sharing the same space.


That only happens when you have two overlapping poly's facing in the same direction (or when you have Culling disabled). Wink
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Starnick
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Joined: 28 Jul 2007
Posts: 611

PostPosted: Fri Apr 02, 2010 12:14 pm    Post subject: Reply with quote

It may be useful for some things, but like everyone else said for most things its better to stay away. Lighting calculations for two sided rendering get expensive, and you may have unintentional results when you do alpha blending.

In alot of cases, what you're trying to make sometimes is done via billboarding in a graphics application (e.g. it always faces the camera, so it doesn't matter if its only one sided). Unless of course you're going for a rather high poly, truly three dimensional feather Razz
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