angle function

double angle(num x1, num y1, num x2, num y2,)

assume p1(x1, y1) is the center, the angle of the line between p1 and p2 rotates from the vertical Y axis line of the coordinates

Implementation

double angle(num x1, num y1, num x2, num y2) {
  final sx = x1 - x2;
  final sy = y1 - y2;
  final dx = sx.abs();
  final dy = sy.abs();
  final d = math.sqrt(dx * dx + dy * dy);
  double angle = (math.asin(dy / d) / math.pi * 180);

  if (x2 >= x1) {
    if (y2 >= y1) {
      angle = 90 + angle;
    } else {
      angle = 90 - angle;
    }
  } else {
    if (y2 >= y1) {
      angle = -(90 + angle);
    } else {
      angle = -(90 - angle);
    }
  }

  return angle;
}