SUBROUTINE SPIDER
C
C	THIS SUBROUTINE CONTROLS THE ACTIONS OF A SPIDER
C
      IMPLICIT INTEGER(A - Z)
      PARAMETER MAXCNT = 24
C SCREEN BOUNDARIES
      PARAMETER LMAR = 2, RMAR = 30, TMAR = 2, BMAR = 23, GMAR = 18
C DIRECTIONALS
      PARAMETER HALT = 0, UP = 1, DOWN = 2, LEFT = 4, RIGHT = 8
      PARAMETER UPL = 10, UPR = 9, DOWNL = 12, DOWNR = 11
C DISPLAYABLE CHARACTERS
	PARAMETER GUNCHR="166, CBODY="140, MSHCHR="146, BULCHR="170
	PARAMETER SPICHR="173, FLECHR="175, SCOCHR="142, PSNCHR="052
	PARAMETER CLHEAD="074, CRHEAD="076, CDHEAD="126
	PARAMETER SHFIN="17, SHFOUT="16, SPACE="40
C QIO FUNCTION CODES
	PARAMETER IOATA="1410, IOWVB="11000, SFSMC="2440
C
      INTEGER*4SCORE, FRESCO, TIMER, SEED, FLETIM, SPITIM, SCOTIM, CNTTI
     *M
      DIMENSION PRL(6), CX(MAXCNT, 12), CY(MAXCNT, 12)
      DIMENSION CLEN(MAXCNT), CDIR(MAXCNT), CRISE(MAXCNT), CBOT(MAXCNT)
      BYTE CNTBRD(BMAR, RMAR), MSHBRD(BMAR, RMAR), PSNBRD(BMAR, RMAR)
      COMMON/DIRCOM/DIRCOD, FIRCOD
      COMMON/CNTCOM/PRL, SCORE, TIMER, SEED, CX, CY, CLEN, CDIR, CRISE, 
     *CBOT, GUNX, GUNY, FRESCO, CNTBRD, MSHBRD, PSNBRD, BULACT, BULX, BU
     *LY, FLETIM, FLEACT, FLEX, FLEY, SPITIM, SPIACT, SPIX, SPIY, SPILR,
     * SCOTIM, SCOACT, SCOX, SCOY, SCODIR, GUNCNT, CNTTIM, BOARD, CNTWAV
C
C	VT100 DISPLAY CONTROL PARAMETER DEFINITIONS
C
CCURSOR POSITION REPORT
CCURSOR UP
CCURSOR DOWN
CCURSOR FORWARD
CCURSOR BACK
CDOUBLE WIDTH LINE
      PARAMETER CUP = 1, CUU = 2, CUD = 3, CUF = 4, CUB = 5, DECDWL = 6,
     * DECDHL = 7, DECRC = 8, DECSC = 9, DECSWL = 10, ED = 11, EL = 12, 
     *SGR = 13, NEL = 14, SCS = 15, SM = 16, RM = 17, ANSI = 18, CPP=19
      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/
C
C	RANDOMLY SELECT NEW SPIDER MOTION. IF SPIDER UNABLE TO MOVE TO
C	THAT LOCATION RETURN.  CLEAR OUT ANY MUSHROOM AT THAT LOCATION.
C
      X = RAN(SEED)
CRANDOM NUMBER IN RANGE 1-4
      RANDX = (X*4) + 1
      X = RAN(SEED)
CRANDOM NUMBER IN RANGE 1-4
      RANDY = (X*4) + 1
      IF (.NOT.(SPILR .EQ. LEFT)) GOTO 2000
CSPIDER IS TRAVELLING TO LEFT...
        NEWX = SPIX + XLADD(RANDX)
CSELECT A RANDOM MOTION
        NEWY = SPIY + YLADD(RANDY)
        IF (.NOT.(NEWY .LT. LMAR)) GOTO 2020
CIF OFF EDGE OF SCREEN, END OF SPIDER
          CALL UVT100(CPP, SPIX, SPIY, SPACE)
          SPIACT = 0
CNEXT SPIDER IN 30 CYCLES
          SPITIM = TIMER + 30
          RETURN
CCHECK FOR ILLEGAL MOVE
2020    CONTINUE
        GOTO 2010
2000  CONTINUE
      IF (.NOT.(SPILR .EQ. RIGHT)) GOTO 2040
CSPIDER IS TRAVELLING RIGHT...
        NEWX = SPIX + XRADD(RANDX)
CSELECT A RANDOM MOTION
        NEWY = SPIY + YRADD(RANDY)
        IF (.NOT.(NEWY .GT. RMAR)) GOTO 2060
CIF OFF EDGE OF SCREEN, END OF SPIDER
          CALL UVT100(CPP, SPIX, SPIY, SPACE)
          SPIACT = 0
CNEXT SPIDER IN 30 CYCLES
          SPITIM = TIMER + 30
          RETURN
CCHECK FOR ILLEGAL MOVE
2060    CONTINUE
C
C	TEST IF LEGAL FOR SPIDER TO MOVE TO NEW LOCATION
C
2040  CONTINUE
2010  CONTINUE
      IF (.NOT.(NEWX .LT. GMAR.OR.NEWX .GT. BMAR)) GOTO 2080
CCAN'T MOVE OUT OF PLAYER'S ZONE
        RETURN
2080  CONTINUE
      IF (.NOT.(CNTBRD(NEWX, NEWY) .GT. 0)) GOTO 2100
CCAN'T MOVE INTO CENTIPEDE
        RETURN
2100  CONTINUE
      IF (.NOT.(MSHBRD(NEWX, NEWY) .GT. 0)) GOTO 2120
CCAN'T MOVE INTO MUSHROOM
CCLEAR MUSHROOM AT THIS LOCATION
        MSHBRD(NEWX, NEWY) = 0
        CALL UVT100(CPP, NEWX, NEWY, SPACE)
        RETURN
C
C	ERASE SPIDER AT OLD LOCATION AND DISPLAY SPIDER AT NEW LOCATION.
C
2120  CONTINUE
      CALL UVT100(CPP, SPIX, SPIY, SPACE)
      SPIX = NEWX
      SPIY = NEWY
      CALL UVT100(CPP, SPIX, SPIY, SPICHR)
      RETURN
      END