// Approximates object as a circle. Set 'radius' to half the size of object squared.

var px, py, dx, dy, t, l;
dx = x2-x1;
dy = y2-y1;

if (dx == 0 && dy == 0)
{
    px = x1;
    py = y1;
}
else
{
    t = min(max(((x-x1)*dx + (y-y1)*dy) / (dx*dx + dy*dy), 0), 1);
    px = x1 + dx*t;
    py = y1 + dy*t;
}

dx = px - x;
dy = py - y;
l = dx*dx + dy*dy;

if (l < radius)
{
    t = sqrt(radius / l);
    x = px - dx*t;
    y = py - dy*t;
}