How does this circle collision detection math work?
- by Griffin
I'm going through the wildbunny blog to learn about collision detection. I'm confused about how the vectors he's talking about come into play.
Here's the part that confuses me:
p = ||A-B|| – (r1+r2)
The two spheres are penetrating by
distance p. We would also like the
penetration vector so that we can
correct the penetration once we
discover it. This is the vector that
moves both circles to the point where
they just touch, correcting the
penetration. Importantly it is not
only just a vector that does this, it
is the only vector which corrects the
penetration by moving the minimum
amount. This is important because we
only want to correct the error, not
introduce more by moving too much when
we correct, or too little.
N = (A-B) / ||A-B||
P = N*p
Here we have calculated the normalised
vector N between the two centres and
the penetration vector P by
multiplying our unit direction by the
penetration distance.
I understand that p is the distance by which the circles penetrate, but I don't get what exactly N and P are. It seems to me N is just the coordinates of the 3rd point of the right trianlge formed by point A and B (A-B) then being divided by the hypotenuse of that triangle or distance between A and B (||A-B||). What's the significance of this?
Also, what is the penetration vector used for? It seems to me like a movement that one of the circles would perform to get un-penetrated.
