Re: Something wrong with this SAT method for finding contact points?

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> Hi! I was wondering if there is a better way for finding the contact
> points in 2D when using SAT. Here's what i currently use:
> 
> Find the two objects positions pos1New and pos2New that represent 
> the positions when the two objects are just touching and are about 
> to collide if moved further. Find the minimum translation vector, 
> let it be vectMTD.
> 
> Take polygon1 in position pos1New and find the minimum of projecting
> it's vertices onto vectMTD. Also store the points that cause this 
> minimum projection measure int list L1.
> Build a separating plane using vectMTD and one of these points 
> detected. Now build a second list(L2) of points that lie on this 
> plane but correspond to polygon2 in position pos2New. 
> 
> If one of the lists has 1 point an the other two then we have 
> vertex-edge case, if  both have one point then we have vertex-vertex 
case.
> If both lists have two points than we have edge-edge case. We 
> calculate a new plane along the edge of the polygons using a normal 
> perpendicular to vectMTD and located in the origin. Next the for 
> points are sorted based on their distance to the plane. The second 
> and third point define the line of collision. 

Hi Adrian,

In 2d there is only edge/vertex and vertex/edge cases. Once you have 
determined which case you have, you take the edge from one object and then 
build another edge from the vertex of the other using some metric to 
choose the other vertex (like vertex which produces most edge overlap, for 
example) and then simply project the vertices of one edge onto the other 
edge (clamping to edge extents) and visa versa, giving you two contact 
points for each object, penetration distances and a single normal (the 
normal from MTD).

Thats what we did anyway :)

Cheers, Paul.
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