cubicTo method

@override void cubicTo(double x1, double y1, double x2, double y2, double x3, double y3,)

Implementation

@override
void cubicTo(
    double x1, double y1, double x2, double y2, double x3, double y3) {
  assert(!_expectsMove);

  // ignore: parameter_assignments
  x1 -= _offsetX;
  // ignore: parameter_assignments
  x2 -= _offsetX;
  // ignore: parameter_assignments
  x3 -= _offsetX;

  // ignore: parameter_assignments
  y1 -= _offsetY;
  // ignore: parameter_assignments
  y2 -= _offsetY;
  // ignore: parameter_assignments
  y3 -= _offsetY;

  if (_quickRejectY(_prevY, y1, y2, y3)) {
    _prevX = x3;
    _prevY = y3;
    return;
  }

  final count =
      _countCubicSegments(_prevX, _prevY, x1, y1, x2, y2, x3, y3, _tolerance);

  final dt = 1.0 / count;
  double t = dt;

  // Compute simple coefficients for the cubic polynomial
  // ... much faster to evaluate multiple times
  // ... At^3 + Bt^2 + Ct + D
  //
  final aX = (x3 - _prevX) + 3 * (x1 - x2);
  final bX = 3 * ((x2 - x1) + (_prevX - x1));
  final cX = 3 * (x1 - _prevX);
  final dX = _prevX;

  final aY = (y3 - _prevY) + 3 * (y1 - y2);
  final bY = 3 * ((y2 - y1) + (_prevY - y1));
  final cY = 3 * (y1 - _prevY);
  final dY = _prevY;

  // we don't need the first point eval(0) or the last eval(1)
  double px = _prevX;
  double py = _prevY;
  for (int i = 1; i < count - 1; ++i) {
    // Horner's method for evaluating the simple polynomial
    final nx = ((aX * t + bX) * t + cX) * t + dX;
    final ny = ((aY * t + bY) * t + cY) * t + dY;
    _clipLine(px, py, nx, ny);
    px = nx;
    py = ny;
    t += dt;
  }
  _clipLine(px, py, x3, y3);
  _prevX = x3;
  _prevY = y3;
}