SUBROUTINE SPIDER
#
#	THIS SUBROUTINE CONTROLS THE ACTIONS OF A SPIDER
#
	IMPLICIT INTEGER (A-Z)
	INCLUDE SY:CNTPED.CMN
	INCLUDE SY:UVT100.DAT
	REAL X,RAN
	DIMENSION XLADD(4),YLADD(4),XRADD(4),YRADD(4)
	DATA XLADD / -1,-1,1,1 /
	DATA YLADD / 0,-1,-1,0 /
	DATA XRADD / -1,-1,1,1 /
	DATA YRADD / 0,1,1,0 /
#
#	RANDOMLY SELECT NEW SPIDER MOTION. IF SPIDER UNABLE TO MOVE TO
#	THAT LOCATION RETURN.  CLEAR OUT ANY MUSHROOM AT THAT LOCATION.
#
	X = RAN(SEED)
	RANDX = (X * 4) + 1		#RANDOM NUMBER IN RANGE 1-4
	X = RAN(SEED)
	RANDY = (X * 4) + 1		#RANDOM NUMBER IN RANGE 1-4
	IF (SPILR == LEFT) [		#SPIDER IS TRAVELLING TO LEFT...
	  NEWX = SPIX + XLADD(RANDX)
	  NEWY = SPIY + YLADD(RANDY)	#SELECT A RANDOM MOTION
	  IF (NEWY < LMAR) [		#IF OFF EDGE OF SCREEN, END OF SPIDER
	    CALL UVT100(CUP,SPIX,SPIY)
	    OUTBUF(LEN+1) = SPACE
	    LEN = LEN + 1
	    SPIACT = 0
	    SPITIM = TIMER + 30		#NEXT SPIDER IN 30 CYCLES
	    RETURN
	    ]				#CHECK FOR ILLEGAL MOVE
	  ]
	ELSE IF (SPILR == RIGHT) [	#SPIDER IS TRAVELLING RIGHT...
	  NEWX = SPIX + XRADD(RANDX)
	  NEWY = SPIY + YRADD(RANDY)	#SELECT A RANDOM MOTION
	  IF (NEWY > RMAR) [		#IF OFF EDGE OF SCREEN, END OF SPIDER
	    CALL UVT100(CUP,SPIX,SPIY)
	    OUTBUF(LEN+1) = SPACE
	    LEN = LEN + 1
	    SPIACT = 0
	    SPITIM = TIMER + 30		#NEXT SPIDER IN 30 CYCLES
	    RETURN
	    ]				#CHECK FOR ILLEGAL MOVE
	  ]
#
#	TEST IF LEGAL FOR SPIDER TO MOVE TO NEW LOCATION
#
	IF (NEWX < GMAR .OR. NEWX > BMAR)
	  RETURN			#CAN'T MOVE OUT OF PLAYER'S ZONE
	IF (CNTBRD(NEWX,NEWY) > 0)
	  RETURN			#CAN'T MOVE INTO CENTIPEDE
	IF (MSHBRD(NEWX,NEWY) > 0) [	#CAN'T MOVE INTO MUSHROOM
	  MSHBRD(NEWX,NEWY) = 0		#CLEAR MUSHROOM AT THIS LOCATION
	  CALL UVT100(CUP,NEWX,NEWY)
	  OUTBUF(LEN+1) = SPACE
	  LEN = LEN + 1
	  RETURN
	  ]
#
#	ERASE SPIDER AT OLD LOCATION AND DISPLAY SPIDER AT NEW LOCATION.
#
	CALL UVT100(CUP,SPIX,SPIY)
	OUTBUF(LEN+1) = SPACE
	LEN = LEN + 1
	SPIX = NEWX
	SPIY = NEWY
	CALL UVT100(CUP,SPIX,SPIY)
	OUTBUF(LEN+1) = SPICHR
	LEN = LEN + 1
	RETURN
	END