decomposeRelativeTransform function

RelativeTransform decomposeRelativeTransform(List<num>? t1)

Implementation

RelativeTransform decomposeRelativeTransform(List<num>? t1) {
  t1 ??= defaultGradientTransform();

  // __        __
  // |a   c   tx|
  // |b   d   ty|
  // --        --
  final double a = t1[0].toDouble();
  final double b = t1.length > 1 ? t1[1].toDouble() : 0;
  final double c = t1.length > 2 ? t1[2].toDouble() : 0;
  final double d = t1.length > 3 ? t1[3].toDouble() : 0;
  final double tx = t1.length > 4 ? t1[4].toDouble() : 0;
  final double ty = t1.length > 5 ? t1[5].toDouble() : 0;

  final double delta = a * d - b * c;

  List<double> translation = [tx, ty];
  double rotation = 0;
  List<double> scale = [0, 0];
  List<double> skew = [0, 0];

  // Apply the QR-like decomposition.
  if (a != 0 || b != 0) {
    final double r = sqrt(a * a + b * b);
    rotation = b > 0 ? acos(a / r) : -acos(a / r);
    scale = [r, delta / r];
    skew = [atan((a * c + b * d) / (r * r)), 0];
  } else if (c != 0 || d != 0) {
    // these are not currently being used.
    final double s = sqrt(c * c + d * d);
    rotation = pi / 2 - (d > 0 ? acos(-c / s) : -acos(c / s));
    scale = [delta / s, s];
    skew = [0, atan((a * c + b * d) / (s * s))];
  } else {
    // a = b = c = d = 0
  }

  return RelativeTransform(
    translation: translation,
    rotation: rotation / pi * 180,
    scale: scale,
    skew: skew,
  );
}