🚀 go-pugleaf

I'm trying to learn more InterViews by extending the example program
"preview.c" so that it's more nearly a true editor.  I didn't get very
far in this before I got stuck on the concepts of damage and repair.
At least that's where I think I'm stuck.

There are allusions to these functions at a few points in the
Reference Manual and in other iv-related papers I've collected, but
nowhere have I've been able to find anything like an explanation
of what they really do, and why.  And I'm further confused about
the possibly related functions, draw and redraw.  

I gather from the August '90 paper "Glyphs: Flyweight Objects for
User Interfaces" that the iv approach is to "...build objects that
will draw themselves whenever necessary".  I've read the Reference
Manual countless times now, and I still can't find any explanation
of this mechanism.  Who decides when it's necessary to redraw?
How can this be forced?

I'd like to find an explanation, and I'd like to solve this specific
problem:

void DocumentView::erase ()
{
 
  printf ("in DocumentView::erase   ");
  printf ("glyphs in buffer: %d\n", page_->count ());

  for (GlyphIndex i=0; i < page_->count (); i++)
     page_->remove (i);


Having removed these glyphs, what do I do to see force the screen
update?

I'll be grateful for any help on this.  
Also, if the source for the editor described in the "Glyphs..."
article is available, I'd sure like to take a look at it.

Thanks.

 - Paul