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# Finding intersections

HI.

I have these circles in my level, which collide with each other(static), and I would like to ask about what would be the best way to blueprint so that it finds the intersection points.
Here’s a visual for reference: What I need is to find the intersection points of the big circle getting collided by the ABC small ones, getting the transform point anywhere in the grayed-out area, and desirable for B and C to have one point where they collide with the big circle and also among themselves(dark gray).

Please leave any comments if something was left unclear. I’d really appreciate your support, thanks in advance.

EDIT: The circles are 3D objects.

Just look at two spheres, sphere A and sphere B. These will give you a general case. Get each sphere’s position vector. For each sphere subtract the other value by it’s value, to get it’s vector normal pointing towards the other sphere. Multiply that value by it’s radius, and add it’s location vector. to get a point on the spheres edge in line with the other sphere. Do that with both spheres. Next you need to make sure they are overlapping, so for sphere A take the points you got and subtract A-B, if the value is negative they are overlapping. Next take that value and divide by 2 this get’s the distance from the edge of the sphere to the overlapping center. Next add that value to the Sphere’s edge vector we got before. This will give the center vector of the grey area.

I will be back later and I can finish with getting the points where the circles hit, hopefully that made sense.

That was just me thinking through the problem, so I haven’t tested to make sure but it should work. Just watch out when subtracting vectors which you subtract from which to make sure you are getting positive when you want and negative when you want.

Thanks for quick answer, I’ll test it out.

EDIT: Alright, this seems to do the task if I know exactly all the information needed about the circles, but what I am aiming for is an automated procedure, with circles(or maybe shapes) various sizes, and really in need of something more advanced but more simple to use. I’m not sure about all the stuff UE offers(also the documentation looks barely half-full), but I’d guess that a smart trigger system would do the trick?

EDIT: I want the big circle to “feel” each actor colliding with it, and give out the location of the point. Thanks in advance once again.