GJK/EPA and hollow shapes

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Numsgil
Posts: 38
Joined: Wed May 14, 2008 5:58 am

GJK/EPA and hollow shapes

Post by Numsgil »

Is there a way to leverage GJK or EPA for hollow shapes?

Imagine this case:
triangleInsideSquare.png
triangleInsideSquare.png (2.67 KiB) Viewed 7596 times
You want to keep the red triangle inside the black square. In the case in the picture you'd want there to be no collision. But vertex A is *almost* touching the edge, so the distance/separating vector should be pretty small.

EPA would return the separating vector from B to the left edge of the square, which is almost what I want but not quite. I'm guessing there's probably something like a modification of EPA that would give the right answer?
bone
Posts: 231
Joined: Tue Feb 20, 2007 4:56 pm

Re: GJK/EPA and hollow shapes

Post by bone »

Wouldn't hollow be the same case as concave? In which case, EPA/GJK aren't really suited to the task.
Numsgil
Posts: 38
Joined: Wed May 14, 2008 5:58 am

Re: GJK/EPA and hollow shapes

Post by Numsgil »

It's perhaps similar, but I'd be very surprised if you couldn't get GJK/EPA to work with some modification. I don't think the Minkowski difference is usable, but some sort of erosion CSG type thing might work instead? It should still produce a convex region, which you should still be able to walk with GJK/EPA.
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