Bouncing balls flashing animation

I modeling balls bouncing physics behavior with matlab. Below is my balls animation code, if i using one ball then bouncing animation is fine, but if i insert more than one ball then balls animation is flashing.

ball_rad = [1,1,1];         % ball radius in metres
ball_pos = [0 10;0 5;0 6];    % ball (x,y) position in metres
ball_vel = [1 1;1 1;1 1];     % ball (x,y) velocity in metres per second
ball_spin = [0,0,0];        % ball spin in radians per second
ball_angle = [0,0,0];       % ball angle in radians

tic
while ~stop
    amount = size(ball_rad);
    for i=1:amount(1,2)
        % draw ball
        ball_h = rectangle('Position', [ball_pos(i,:)-[ball_rad(i) ball_rad(i)] ball_rad(i)*2 ball_rad(i)*2], 'Curvature', [1 1]);
        offset = ball_rad(i) * [cos(ball_angle(i)) sin(ball_angle(i))];
        p1 = ball_pos(i,:) + offset;
        p2 = ball_pos(i,:) - offset;
        line_h = line([p1(1) p2(1)], [p1(2) p2(2)], 'Color', 'k');

          % draw frame and pause to achieve required fps

          drawnow
          tic
          % erase ball
          delete(ball_h);
          delete(line_h);
          if exist('plot_h','var'), delete(plot_h); clear plot_h, end

          % Update vertical ball velocity from gravitational acceleration
          ball_vel(i,:) = ball_vel(i,:) + [0 g/fps];
          ball_pos_old = ball_pos(i,:);
          % Update ball position from ball velocity
          ball_pos(i,:) = ball_pos(i,:) + ball_vel(i,:)/fps;
          % Update ball angle from ball spin (angular velocity)
          ball_angle(i) = ball_angle(i) + ball_spin(i)/fps;

          % loop through surfaces
          for s = 1 : num_surfaces
              surface = surfaces{s};

              % compute surface normal such that it's on the ball's side
              normal = [surface(2,2)-surface(1,2) surface(1,1)-surface(2,1)];
              normal = normal / norm(normal);
              vel_dir = ball_vel(i,:) / norm(ball_vel(i,:));
              if normal*vel_dir' < 0
                  normal = -normal;
              end

              % compute the position of the edge of the ball nearest the surface
              edge_offset = normal * ball_rad(i);
              edge_pos_old = ball_pos_old + edge_offset;
              edge_pos = ball_pos(i,:) + edge_offset;

              % ball collides with surface if the line segment between its
              % current and old position intersects the surface
              if lines_cross(edge_pos_old, edge_pos, surface(1,:), surface(2,:))
                  ball_vel_old = ball_vel(i,:);

                  % compute the collision point from the point of intersection
                  intersect_pt = lines_intersection(edge_pos_old, edge_pos, surface(1,:), surface(2,:));

                  % rotate velocity vector onto horizontal surface
                  co = normal(2);
                  si = normal(1);
                  rot = [-co -si; si -co];
                  ball_vel_rot = ball_vel(i,:) * rot;

                  % update velocity parallel to surface and spin
                  ball_vel_rot_tmp = (1/7)*(5 - 2*h_restitution)*ball_vel_rot(1) - (2/7)*(1 + h_restitution)*ball_rad(i)*ball_spin(i);
                  ball_spin(i) = -(5/(7*ball_rad(i)))*(1 + h_restitution)*ball_vel_rot(1) + (1/7)*(2 - 5*h_restitution)*ball_spin(i);
                  ball_vel_rot(1) = ball_vel_rot_tmp;
                  % update velocity perpendicular to surface
                  ball_vel_rot(2) = ball_vel_rot(2) * -restitution;
                  % rotate velocity vector back to original surface
                  ball_vel(i,:) = ball_vel_rot * rot';

                  % update position relative to intersection to correct overshoot
                  overshoot = edge_pos - intersect_pt;
                  overshoot = ball_vel(i,:) * norm(overshoot) / norm(ball_vel_old);
                  ball_pos(i,:) = intersect_pt + overshoot - edge_offset;
              end
          end
      end
  end