anchor_geometry_in_navigator.dart

Matrix4 getAnchorToNavigatorTransform(RenderObject anchor, RenderObject navigator) {
  // These two transforms project points from the local coordinate spaces of their 
  // respective RenderObjects to the global coordinates space.
  Matrix4 anchorTransform = anchor.getTransformTo(null);
  Matrix4 navigatorTransform = navigator.getTransformTo(null);
  // This transform projects points from the local coordinates space of [anchor]
  // to the global coordinate space and from there to the local coordinate space
  // of [navigator] in one step.
  return anchorTransform..multiply(Matrix4.tryInvert(navigatorTransform));
}

// This method assumes that [anchor] is a [RenderBox], and returns a [Rect] which
// describes the dimensions of [anchor] in [navigator].
// [RenderBox] is the most common sub class of [RenderObject], where every instance
// is laid out as a box and has a [Size].
Rect getAnchorRectInNavigator(RenderObject anchor, RenderObject navigator) {
  Matrix4 transform = getAnchorToNavigatorTransform(anchor, navigator);
  Rect anchorRect = Offset.zero & (anchor as RenderBox).size;
  return MatrixUtils.transformRect(transform, anchorRect);
}