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# Creating triangles from line strips

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Hi all, I have written a rudimentary .dxf converter (to DX), and have come to the problem of taking my line strips and creating triangles for rendering in DX. I have had a quick look around for tripling algorithms but I haven''t found anything which I can use (most google results telling me that wonderful products can triple for me!). Could someone please help me out - provide some other key-words to search on. Thanks, Steele.

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Ok, I have come along a bit with this so I can be a bit more specific. The part I am having trouble with is, given a particular line, how to determine which side of the line is "inside" the polygon.
      C+--+  +------+|  |  |      || A+--+B     ||            ||   +--+  +--+|   |  |  |+---+  +--+

So that working around my line strip in clockwise order (this is arbitrary) from A to B, how can I tell that the triangle ABC is not within the polygon?
Thanks for any help,
Steele.

[edited by - Crow-knee on February 9, 2004 7:03:46 PM]

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Look for tesselation of concave polygon on google.

For your particular question, test if B is back facing or front facing segment [AC].
- in 2d this should be testing the sign of the line equation applied on B : a*xB + b*yB +c (I dont remember how to compute a, b & c coeffs).
- in 3d, the same with the plane equation : a*xB + b*yB + c*zB + d, where a,b,c are the coordinates of the normal vector, d can be found with one point of the plane

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