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OpenGL - triangles n' normals

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Started by Gary_80 May 25, 2011 11:27 AM

2 comments, last by Gary_80 12 years, 10 months ago

Gary_80

100

Author

May 25, 2011 11:27 AM

Hi,

if i have a cube face i.e

0---------------------1
| |
| |
| |
| |
2---------------------3

preferable i want it as two triangles with a diagonal splitting the middle,
my question is is does it mater which way the diagonal goes, and how would the triangles be ordered i.e. 0,1,2 and 213,

Also does the ordering effect the light once the normals has been calculated?

thanks

bubu LV

1,436

May 25, 2011 11:37 AM

It doesn't matter. Rendering & light will be same no matter in what order you render triangles.

lauris71

841

May 25, 2011 11:48 AM

The order of triangles and the direction of diagonal are not important.
The order of vertices of triangle - clockwise or counterclockwise - is. At least if you are rendering solid body (and normally you are). One side of the triangle is facing outside the body, the other inside. Normally the inside facing triangles are discarded by culling.
If you calculate the normal by taking cross product of two side-vectors of the triangle, the direction of the normal also depends on the order of vertices.
Keep all your triangles in counter-clockwise order if looked from outside, and everything should be OK.

Lauris Kaplinski

First technology demo of my game Shinya is out: http://lauris.kaplinski.com/shinya
Khayyam 3D - a freeware poser and scene builder application: http://khayyam.kaplinski.com/

Gary_80

100

Author

May 25, 2011 11:49 AM

ideal, thanks MartinsM

OpenGL - triangles n' normals

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