Ray-Capsule Intersection

// the diff float variable is used after this method.// if diff is < 0, a sphere intersect is done on the// beginning of the capsule line. If its > 0, on the end of it// If it is == 0.0, the line completely missed the capsuleVEC contact_point;// Only check if ray is not parallel with the cylinderFLOAT diff = DOT( ray_directionection , cylinder_direction );if(diff < -0.99999f || diff > 0.99999f){	diff = -diff;	return FALSE;}// Get the shared plane's normal of both linesVEC shared_plane = CROSS( ray_direction, cylinder_direction );// Get the normal that the cylinder line is resting onVEC cylinder_normal = CROSS( shared_plane, cylinder_direction );cylinder_normal.Normalize();// Get the intersect distance from ray -> cylinder's planediff = DOT( cylinder_normal, ray_direction );dist = ( DOT( cylinder_position, cylinder_normal ) - DOT( ray_position, cylinder_normal) ) / diff;// Get the point on the ray which intersects this planecontact_point = ray_position + ( ray_direction * dist );// Get the closest point on the infinite cylinder line to this intersect pointdiff = DOT( cylinder_direction, contact_point - cylinder_position );VEC closest_on_cyl = cylinder_position + (cylinder_direction * diff);// Intersect a sphere from this position, but angled straight toward cylinder// THIS IS THE PART that feels the most hacked - because of my lack of math skills :)VEC sp_position = contact_point - (cylinder_normal * cylinder_radius);sp_position = closest_on_cyl - sp_position;diff = DOT( cylinder_normal, sp_position );dist = diff * diff - ( sp_position.LengthSquared() - (cylinder_radius * cylinder_radius) );if(dist < 0.0f){	diff = 0.0f;	return FALSE;}dist = diff - sqrtf( dist );if(dist < -0.0001f){	diff = 0.0f;	return FALSE;}// Insersect the plane again, but move the plane forward according to sphere shape - so we are intersecting an infinite cylinderVEC plane_position = cylinder_position + ( cylinder_normal * (cylinder_radius - dist) );diff = DOT( cylinder_normal, ray_direction );dist = ( DOT( plane_position, cylinder_normal ) - DOT( ray_position, cylinder_normal ) ) / diff;// If the ray cannot reach the infinite cylinder, we are doneif( dist > ray_length ){	diff = 0.0f;	return FALSE;}// Force this point back onto raycontact_point = ray_position + (ray_direction * dist);// Make sure the closest point on cylinder is now on the linediff = DOT( cylinder_direction, contact_point - cylinder_position );if(diff < -0.0001f || diff > cyl_len + 0.0001f)	return FALSE; // diff can now be used to place a sphere when this method returns// We hitreturn TRUE;