NAME
        BltPattern --  Using standard drawing rules for areafill,
                                         blit through a mask.

   SYNOPSIS
       BltPattern(rp, mask, xl, yl, maxx, maxy, bytecnt)
                  a1,  a0   d0  d1   d2   d3     d4

        void BltPattern
           (struct rastport *, void *, short, short, short, short, short);

   FUNCTION
       Blit using drawmode,areafill pattern, and mask
       at position rectangle (xl,yl) (maxx,maxy).

   INPUTS
       rp    -  points to the destination rastport for the blit.
       mask  -  points to 2 dimensional mask if needed
                if mask == NULL then use a rectangle.
       xl,yl -  coordinates of upper left of rectangular region in rastport
       maxx,maxy - points to lower right of rectangular region in rastport
       bytecnt - BytesPerRow for mask

   RESULT

   SEE ALSO
        areaend()