Hoping someone could help me understand the algorithm to finding edges. I've been reading and re-reading about shadow volumes and having a really tough go of it for some reason. Namely in the edge finding algorithm. The latest material I'm looking over comes from the book "Mathematics for 3D Game Programming and Computer Graphics" (3rd Edition) by Eric Lengyel. In it he displays the code behind a BuildEdges function. But he does what I've seen done so many other times with Shadow Volumes. He seems to base some stuff of the vertex-index of the points on a triangle and he furthers this even further by checking if the index number is greater than or less than the previous one. Um... what?. The index number, from my personal experience, is just a rudimentary number that correlates to a 3-float-value (x, y, z) in a vertex-table list that only lists vertex values once -- that is, a **unique** vertex list. But even if the actual vertex-list was not one of uniqueness of it's entries, what good would checking an index number's ordinal value be? From what I can tell, the indices (The order of the vertices in that list) has no rhyme or reason they're just in there in the order the 3D modeling program sees as it's looping through the geometry to export. I don't really understand how the index's number is helpful...If someone could shed some light on this, I'd really appreciate it; thanks!

P.S. I'd post the function, but I'm not sure if that's something the publisher would mind. I can't see why they wouldn't given it's only one function is a fairly thick book, but I'll defer that to the board mods.

-- StakFallT

**Edited by StakFallT, 08 June 2014 - 02:54 PM.**