If you want something a little faster, you could project the line defining your slicing plane and all the mesh's points onto a virtual plane perpendicular to the camera's point of view, then compute which side of the slicing line each vertex resides and flag it as -1, 0, or 1 for below, on, or above the line respectively. As you traverse the edges of the mesh, compare the flags of the two vertices comprising the edge to see if they are on opposite sides of the slicing line. If yes, then select the edge. Since you know the slicing line passes through the edge, then by definition it must intersect both triangles sharing the edge (unless the edge is parallel to the slicing line). That implies exactly one other edge of each triangle intersects with the slicing line. So test the next available edge of each. Regardless of the outcome of the test, you know which 2 edges of the triangle intersect the slicing line, so you can skip testing the 3rd. If you have enough information flagged, you may be able to extend the implication to neighboring triangles to eliminate those which share the edge which does not intersect the slicing line, and likewise, more rapidly walk the mesh to find the other edges that do. It should be obvious you'll need a data structure which keeps track of which edges/triangles you've visited. If you extend the logic to a 2nd slicing line perpendicular to the first and record left/on/right side of the 2nd slicing line, you have an algorithm for finding intersection of a point inside of a triangle. A little unconventional, but it works.
With some analysis and deduction, you can speed up the algorithm a lot more. Matt ------ Softimage Mailing List. To unsubscribe, send a mail to softimage-requ...@listproc.autodesk.com with "unsubscribe" in the subject, and reply to confirm.
