gistfile1.txt

  GimpCagePoint point;
  GimpCagePoint *A, *B;
  GimpVector2   *AB, *AD;
  gdouble       lAB, lAD, angle, alpha, beta;

  g_return_if_fail (GIMP_IS_CAGE_CONFIG (gcc));
  g_return_if_fail (point_number <= gcc->cage_points->len);
  g_return_if_fail (point_number >= 0);

  point.src_point.x = x + DELTA;
  point.src_point.y = y + DELTA;

  A = &g_array_index (gcc->cage_points, GimpCagePoint, point_number);
  B = &g_array_index (gcc->cage_points, GimpCagePoint, point_number+1);
  gimp_vector2_sub (AB, B, A);
  gimp_vector2_sub (AD, point.src_point, A);
  lAB = gimp_vector2_length (AB);
  lAD = gimp_vector2_length (AD);

  angle = arcsin ((B->src_point.y - A->src_point.y) / lAB) + arcsin ((y - A->src_point.y) / lAD);
  alpha = lAD * cos (angle);
  beta = lAB * sin (angle);

  point.dest_point.x = x + DELTA;
  point.dest_point.y = y + DELTA;

  g_array_insert_val (gcc->cage_points, point_number, point);

  gimp_cage_config_compute_scaling_factor (gcc);
  gimp_cage_config_compute_edges_normal (gcc);