User Information:

Cinema 4D Version: R15

Platform: Mac ;

Language(s) : C++ ;

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Are the members of a CPolygon struct (a, b, c, and d) always guaranteed to be in sequence (ie, a -> b -> c -> d for a quadrangle), and/or guaranteed to have a specific winding order (clockwise or counterclockwise)?

-CMPX

]]>User Information:

Cinema 4D Version: R15

Platform: Mac ;

Language(s) : C++ ;

---------

Are the members of a CPolygon struct (a, b, c, and d) always guaranteed to be in sequence (ie, a -> b -> c -> d for a quadrangle), and/or guaranteed to have a specific winding order (clockwise or counterclockwise)?

-CMPX

]]>A CPolygon is a structure of point indices a, b, c, d, in that very order. Whether the polygon indices have

a clockwise or counterclockwise order is not the important question, since that depends on the side you

view the polygon from. The **polygon normal** is actually defined as the side of the polygon from which you

look at it so that its points a, b, c (and eventually d, for a quadrangle) are arranged clockwise.

-N

]]>Thanks for the reply.

So the following is always true (for a single quadrangle polygon)?:

A: has neighbours B and D

B: has neighbours A and C

C: has neighbours B and D

D: has neighbours A and C

Like, B will never have a direct connection to D (for a quadrangle), correct?

-CMPX

]]>If C and D are not the same then we have quadrangle that may look like this one:

http://www.mathsteacher.com.au/year7/ch09_polygons/04_quad/Image11005.gif

Note that if C and D are the same (vertex index), then the polygon is a triangle: a->b->c/d. If the vertex index is updated for either c or d, you probably want to do the same for the other to maintain as a triangle.

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