screen and redisplay

[<don...@is...>]

I don't understand what this is all about.
I thought that clisp had no idea about screens and was just running a
top level REP loop connected to a set of character streams.

 > +global void resize_screen (int lines, int columns) {
 > +  rows = lines; cols = columns;
 > +  if (curr->image) redisplay();
 > +}

Under what circumstance would curr->image be true?