⌂ Displaying grob ancestry

When working with grob callbacks, it can be helpful to understand a grob's ancestry. Most grobs have parents which influence the positioning of the grob. X- and Y-parents influence the horizontal and vertical positions for the grob, respectively. Additionally, each parent may have parents of its own.

Unfortunately, there are several aspects of a grob's ancestry that can lead to confusion:

• The types of parents a grob has may depend on context.
• For some grobs, the X- and Y-parents are the same.
• A particular ancestor may be related to a grob in multiple ways.
• The concept of generations is misleading.

For example, the System grob can be both parent (on the Y-side) and grandparent (twice on the X-side) to a VerticalAlignment grob.

This macro prints (to the console) a textual representation of a grob's ancestry.

When called this way:

{ \once \override NoteHead.before-line-breaking = #display-ancestry c }

The following output is generated:

NoteHead
X,Y: NoteColumn
     X: PaperColumn
        X,Y: System
     Y: VerticalAxisGroup
        X: NonMusicalPaperColumn
           X,Y: System
        Y: VerticalAlignment
           X: NonMusicalPaperColumn
              X,Y: System
           Y: System