java swing intersection line with circle point [duplicate]

Given: a circle with center C=[x2,y2] and radius R a line segment from C to B=[x1,y2] calculate their intersection.

This is easy since one of the endpoints is the center of the circle. You have to walk the distance of R from C towards B. The distance guarantees you will end up on the circle and the direction guarantees you will end up on the ray C->B. You still need to check if the intersection lies on the segment.

Here is the pseudocode if you have a vector library

- offset = B-C - if length_square(offset) < R^2 output "no intersection" - offset_a = normalize(B-C) * R - output C + offset_a 

Without a library, the code is longer:

- off_x = x1-x2; - off_y = y1-y2; - ls = off_x*off_x + off_y*off_y - if ls < R*R -- return an empty array, meaning "no intersections" - scale = R / sqrt(ls) - res_x = off_x * scale + x2 - res_y = off_y * scale + y2 - return [[off_x, off_y]]