applyParentOffset method

@override void applyParentOffset(Offset offset)

Calls super method, then adds the passed offset to the locally-kept slot offsetOfPotentiallyRotatedLabel.

In more details: After calling super, rotate the point at which label will start painting - the offset + _tiltedLabelEnvelope.topLeft - by the tilt angle against the tilt (this angle is represented by _labelTiltMatrix inverse).

In non-tilted labels, the _tiltedLabelEnvelope was created as

  ui.Offset.zero & _textPainter.size, // offset & size => Rect

so the _tiltedLabelEnvelope.topLeft is always origin (0.0, 0.0). In addition, the _labelTiltMatrix is identity, so this method will set

  offsetOfPotentiallyRotatedLabel = offset

to the value of offset (large, after all parent offsets applied).

In the tilted labels, the _tiltedLabelEnvelope.topLeft is a small value below origin such as 0.0, 30.0, and offset is also large, after all parent offsets applied. In this situation, the non-zero _tiltedLabelEnvelope.topLeft represent the needed slight 'shift down' of the original offset at which to start painting, as the tilted labels take up a bigger rectangle.

Implementation

// todo-01-morph : this implementation only works for tilting in [XContainer] because first call to it is
//                 made in [XContainer.layout], after label container is created, as
//                    `xLabelContainer.applyParentOffset(labelLeftTop + xLabelContainer.tiltedLabelEnvelopeTopLeft)`.
//                 In this first call(s), the result of offsetOfPotentiallyRotatedLabel is the rotated
//                    value, which is OVERWRITTEN by the last call described below;
//                    also, the accumulated non-rotated this.offset is kept on super slot
//                    This is what we want - we want to keep the non-rotated this.offset on super slot,
//                    and only do the rotation on the last call (last before paint)
//                 The last call is made in [ChartTopContainer.layout] inside
//                     `xContainer.applyParentOffset(xContainerOffset)` as
//                 as
//                    for (AxisLabelContainer xLabelContainer in _xLabelContainers) {
//                      xLabelContainer.applyParentOffset(offset);
//                    }
//                 which calculates and stores the rotated value of the accumulated non-rotated this.offset
//                 into offsetOfPotentiallyRotatedLabel; which value is used by paint.
@override
void applyParentOffset(ui.Offset offset) {
  super.applyParentOffset(offset);

  // todo-01-morph : This should be part of new method 'findPosition' in the layout process
  // Next, _rotateLabelEnvelopeTopLeftToPaintOffset:
  // Transform the point where label painting starts against the tilt of labels.
  // No-op for non-tilted labels, where _labelTiltMatrix is identity,
  //   and  _tiltedLabelEnvelope.topLeft is center = Offset.zero.
  vector_math.Matrix2 canvasTiltMatrix = _labelTiltMatrix.clone();
  canvasTiltMatrix.invert();

  offsetOfPotentiallyRotatedLabel = geometry.transform(
    matrix: canvasTiltMatrix,
    offset: (this.offset),
  );
}