Graphical Window Sprites
version 1 by Erik Temple
Part 9 - Workaround for handling empty windows
[Currently, if a figure-name variable is not explicitly defined, Inform substitutes the cover art (resource ID #1). Practically, this means that it is impossible to test for an undefined figure-name, and thus it is also impossible to call an image-drawing rule without it drawing something. This workaround allows us to explicitly define a figure-name as referring to no-figure. We should explicitly say that the currently shown picture is no-picture if we do not wish to have a background image.
Replace this section in your source text if it becomes unnecessary or redundant through changes to Inform or Simple Graphical Window]
To decide which figure-name is no-picture: (- 0 -).