PROCgo(cm$,coun%) (a type of turtle drawing tool )

And here is the final version that Zaphod (from the old BBC4W forum offered to modernize
make more efficient. It wont draw exactly the same angles, but it is more flexible a tool.
This was added to RETROLIB 10 later in 2016. (you should be able to put the main program I supplied above with this code to see the diffrences)

     DEFPROCgo(cm$,coun%)
     REM Simplified. Line draws the right color and right length now. Much faster. Zaphod
     PRIVATE x%,y%,pen%,c$
     REM x% ,y% are already in @vdu.p.x%, @vdu.p.y% so are not needed to be kept separately as PRIVATE variables
     REM @vdu.g.x has all the color details. BB4W Help "System Variables"
     LOCAL xinc%,yinc%,dist%
     CASE cm$ OF
       WHEN "up" : pen%=1
       WHEN "down" : pen%=0
       WHEN "fill" : FILL x%,y%
       WHEN "c" : c$=STR$(coun%):PROCcolor("f",c$)
     ENDCASE
     dist%=INT(coun%/SQR(2)+0.5) REM round to the nearest pixel for 45° angles
     CASE cm$ OF
       WHEN "n" : yinc%=coun%  : xinc%=0
       WHEN "s" : yinc%=-coun% : xinc%=0
       WHEN "e" : yinc%=0  : xinc%=coun%
       WHEN "w" : yinc%=0  : xinc%=-coun%
       WHEN "ne" :yinc%=dist%  : xinc%=dist%
       WHEN "nw" :yinc%=dist%  : xinc%=-dist%
       WHEN "sw" :yinc%=-dist%  : xinc%=-dist%
       WHEN "se" :yinc%=-dist%  : xinc%=dist%
     ENDCASE
     IF pen% =0 IF (ABS(yinc%)+ABS(xinc%))<>0 THEN LINE x%,y%,x%+xinc%,y%+yinc%
     x%+=xinc%:y%+=yinc%
     ENDPROC