BackPat
void BackPat(newPat );
PatPtr newPat ; address of a Pattern structure
BackPat sets the background pattern, which is used by all Quickdraw erase
operations.
newPat is the address of an 8-byte Pattern structure.
Returns: none

Notes: This replaces the 8-byte bkPat field of the active GrafPort.
You may use one of the Quickdraw global patterns, white, gray, ltGray,
dkGray, or black:
BackPat( dkGray ); /* external constant */
Or you can create a pattern and use that:
Pattern myPat;
StuffHex( &myPat, "\p0202020404040808" );
BackPat( &myPat );
Or you can go for the current desktop pattern (as set by the user via the
Control Panel DA).
BackPat( DeskPattern ); /* defined in Windows.h */
Or you can use one of the Standard Patterns by looking it up in the system
resource file:
Pattern myPat; /* structure to hold pattern */
GetIndPattern( &myPat, sysPatListID,12 ); /* brickwork */
BackPat( &myPat );