Install a backfill hook into the LayerInfo structure. This backfill hook will be called to clear the areas where there is no layer. It will be used for every layer.
INPUTS
li
pointer to layer info
RESULT
If there was a backfill hook installed before it will be returned. LAYERS_BACKFILL will be returned if the default backfill hook was installed, LAYERS_NOBACKFILL if there was nothing to be called for clearing an area.
EXAMPLE
SEE ALSO
NOTES
The hook is not called immediately. It will be called for those areas that have to be cleared when layers move away from those areas.
BUGS
INTERNALS
HISTORY
28.02.1999 bergers
All functions use the backfill or blank hook to fill cleared or new areas.