A way of doing matrix transformations on a Transform2D

[duck-dev-go]

Problem to solve

Currently it seems you cannot modify the matrix of a transform because each transformation resets the matrix. In our case we have a grid that consists of tiles that we want to transform with a matrix. This is currently in the Transform2D

  /// The total transformation matrix for the component. This matrix combines
  /// translation, rotation, reflection and scale transforms into a single
  /// entity. The matrix is cached and gets recalculated only as necessary.
  ///
  /// The returned matrix must not be modified by the user.
  Matrix4 get transformMatrix {
    if (_recalculate) {
      // The transforms below are equivalent to:
      //   _transformMatrix = Matrix4.identity()
      //       .. translate(_position.x, _position.y)
      //       .. rotateZ(_angle)
      //       .. scale(_scale.x, _scale.y, 1)
      //       .. translate(_offset.x, _offset.y);
      final m = _transformMatrix.storage;
      final cosA = math.cos(_angle);
      final sinA = math.sin(_angle);
      m[0] = cosA * _scale.x;
      m[1] = sinA * _scale.x;
      m[4] = -sinA * _scale.y;
      m[5] = cosA * _scale.y;
      m[12] = _position.x + m[0] * _offset.x + m[4] * _offset.y;
      m[13] = _position.y + m[1] * _offset.x + m[5] * _offset.y;
      _recalculate = false;
    }
    return _transformMatrix;
  }

Proposal

I'm not sure how it works exactly but I would like to see maybe a setter for the matrix that either updates the position, scale and rotation so it will work with recalculation or during recalculation the previous matrix should not be overridden.

[spydon]

This is also posted on Stackoverflow if anyone wants more context.

[fwh1990]

And here is no way to set skew property from PositionComponent.

[spydon]

And here is no way to set skew property from PositionComponent.

This is unrelated to this issue, you can open a separate issue for it if you want.

If there are more people asking for skew we'll add that too, but you are actually the first one. :slightly_smiling_face: You can perform a skew manually until then by overriding render and calling canvas.skew.

[st-pasha]

Currently Transform2D is a combination of a translation, rotation and scaling. Crucially, there are many places in the code where we rely on this fact, the code that would work incorrectly if transform allowed skews or non-Z rotations, or anything else custom.

I would suggest not to add any such extra functionality to Transform2D -- it would be more error-prone and less efficient than the current implementation. If really needed, a new class Transform3D can be created to handle such advanced cases.