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*On 23/02/2005 at 17:24, ***xxxxxxxx** wrote:

Well, one way is to find two vertex references shared between polygons. If two polygons both reference the same two vertices, then they MUST share an edge (or a degenerate edge = point (where both sets of shared vertices are equivalent vectors). This will NOT work if the polygons have equivalent vertices, but unshared references (e.g.: right next to each other, but not welded). Then you'd also have to include vector comparisons between vertices.

Clarification:

Polygons contain reference indices into a vertex array (point array), not the actual vertices themselves.

So, if polygon pA references vertices (8,9,11,12) and polygon pB references vertices (24,11,9,13), they share an edge at (9,11).