This is an entity with a radius. Attributes x and y point to the center of the circle.

Each point on the circle is this distance from the center, at ($circ->x, $circ->y)

Anything in Collision::2D::Entity.

See Collision::2D::Entity->collide

 print 'boom' if $circle->collide($rect);
 print 'zing' if $circle->collide($circle);
 print 'yotz' if $circle->collide($grid);

See Collision::2D::Entity->intersect

 print 'bam' if $circle->intersect($rect);
 # etc..