CAD tip # 897:

(c:rpref "ropt" STYPE ALIAS RSRVD TSAMP MINB MAXB 
 TOSSBACK BACKNORM RAYDEPTH)

STYPE=  "ascan" or "aray" 
ALIAS=  1   NHNV
        2   AHNV
        3   AHSV  (2x2)
        4   AHSV3 (3x3)
        5   AHSV4 (4x4)
RSRVD=  0   !MUST be zero
TSAMP=  1   Point
        2   Linear
        3   Mip map
MINB=   real    !Shadow map min bias
MAXB=   real    !Shadow map max bias
TOSSBACK= 0 FALSE  !Off
          1 TRUE   !On
BACKNORM= 0 FALSE  !Off
          1 TRUE   !On
RAYDEPTH= int   !Number of bounces a ray can take

BUGS:
You must turn off the Render Information Dialog while using this API.

Bringing up the Rendering Information or
Rendering Preferences dialogresets these values
to their database values if a rPlus renderer is
the current renderer.

Calling the API will set all values except
RAYDEPTH which is set only if STYPE == "ARAY".

EXAMPLES:

   (c:rpref "TOGGLE" "SKIPRDLG" "OFF")        !Turn off Rend Info Dlg
   (c:rpref "ROPT" "ARAY" 2 0 2 2.0 4.0 0 1 3)  !Defaults, raydepth set
   (c:rpref "ROPT" "ASCAN" 2 0 2 2.0 4.0 0 1 3) !Defaults, raydepth not set
   (c:rpref "ROPT" "ASCAN" 2 NIL 2 NIL NIL 0 1 3) !Shows values skipped
   (c:rpref "ROPT" "ARAY" 2 NIL 2)              !Shows values skipped & quick end