Kolizja koła z prostokątem

bool IsCollision( const BallClass & Ball, const ObstacleClass & Obstacle )
{
    float x0 = Ball.x;
    float y0 = Ball.y;
    float x1 = Obstacle.x1;
    float y1 = Obstacle.y1;
    float x2 = Obstacle.x2;
    float y2 = Obstacle.y2;
    float n = fabs(( x2 - x1 ) *( y1 - y0 ) -( x1 - x0 ) *( y2 - y1 ) );
    float d = sqrt(( x2 - x1 ) *( x2 - x1 ) +( y2 - y1 ) *( y2 - y1 ) );
    float dist = n / d;
    if( dist > Ball.r ) return false;
   
    float d1 = sqrt(( x0 - x1 ) *( x0 - x1 ) +( y0 - y1 ) *( y0 - y1 ) );
    if(( d1 - Ball.r ) > d ) return false;
   
    float d2 = sqrt(( x0 - x2 ) *( x0 - x2 ) +( y0 - y2 ) *( y0 - y2 ) );
    if(( d2 - Ball.r ) > d ) return false;
   
    return true;
}