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single sided triangles

OpenGL

Started by SelethD Nov 1, 2005 at 12:56 PM 6 replies 650+ views

Original Post

SelethD

177

SelethD

Nov 1, 2005 at 12:56 PM

This seems like its probably a very easy solution, but I just dont know enough about OpenGL to do it. When I draw a triangle, I can see it from both sides. I dont want this, since I will have solid objects and the back side will never be seen. What do I need to set or enable to only draw the 'front' of the triangle? thanks

Sneftel

296

Sneftel

Nov 1, 2005 at 12:57 PM

look up glCullMode.

tychon

Nov 1, 2005 at 12:58 PM

glEnable( GL_CULL_FACE ), I think it was. There's a way to set whether a face is defined by CW or CCW formation, but I can't remember it off hand.

Promit

Mod

1,082

Promit

Nov 1, 2005 at 12:59 PM

glFrontFace would be the last part of the puzzle.

SelethD

Author

177

SelethD

Nov 1, 2005 at 1:01 PM

ok, thanks ill experiment from here, :)

swiftcoder

Mod

2,296

swiftcoder

Nov 1, 2005 at 1:04 PM

If you haven't reached it already,

glEnable(GL_CULL_FACE);glFrontFace(GL_CCW); // or GL_CW depending on whether you specify the vertices// of the triangle in counter-clockwise or clockwise order.

should do the trick ;)

SelethD

Author

177

SelethD

Nov 1, 2005 at 2:41 PM

Is it necessary to do this, I mean is there a performance gain in culling the back faces?

swiftcoder

Mod

2,296

swiftcoder

Nov 1, 2005 at 2:45 PM

Quote:
Original post by SelethD
Is it necessary to do this, I mean is there a performance gain in culling the back faces?

Yes, there is. Basically it just cuts down on the number of primitives being sent down the graphics pipeline.
It is also often used to prevent graphical artifacts from appearing in various situations.

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