.TITLE  VXGRID
        .GLOBL  VXGRID
        .GLOBL  VBSET,VSBSET,VCNGT
        .PSECT  VXDES,RW,D,GBL,REL,OVR
XFAC:   .BLKW   2
XOFF:   .BLKW   2
XTYPE:  .BLKW   1
XMAXB:  .BLKW   1
XSMINB: .BLKW   1
XSMAXB: .BLKW   1
XSNOWB: .BLKW   1
        .PSECT
        .PSECT  VXADES,RW,D,GBL,REL,OVR
XAFDU:  .BLKW   2
XADDU:  .BLKW   2
XADDB:  .BLKW   2
XAFDB:  .BLKW   1
XANDB:  .BLKW   1
XAIND:  .BLKW   1
XAGRID: .BLKW   1
XANGB:  .BLKW   1
XAING:  .BLKW   1
XATICK: .BLKW   1
XANTB:  .BLKW   1
XAINT:  .BLKW   1
        .PSECT
        .PSECT  VYDES,RW,D,GBL,REL,OVR
YFAC:   .BLKW   2
YOFF:   .BLKW   2
YTYPE:  .BLKW   1
YMINB:  .BLKW   1
YMAXB:  .BLKW   1
        .PSECT
        .PSECT  VYADES,RW,D,GBL,REL,OVR
YAFDU:  .BLKW   2
YADDU:  .BLKW   2
YADDB:  .BLKW   2
YAFDB:  .BLKW   1
YAGRID: .BLKW   1
YATICK: .BLKW   1
        .PSECT
        .PSECT  VPNTBF,RW,D,GBL,REL,OVR
RPSPP:  .BLKW   1
PNTBUF: .BLKW   1
        .PSECT  VPLTBF,RW,D,GBL,REL,OVR
PLTBUF: .BLKW   1
        .PSECT  VPLTYG,RW,D,GBL,REL,OVR
PLTYGB: .BLKW   1
        .PSECT
R0=%0
R1=%1
R2=%2
R3=%3
R4=%4
R5=%5
SP=%6
PC=%7
BEGBYT: .WORD   0
ENDBYT: .WORD   0
GRD:    .WORD   0
BYTE:   .WORD   0
ARG1:   .WORD   0
ARG2:   .WORD   0
VXGRID: TST     XSNOWB
        BNE     L805
        JMP     L1000
L805:   CMP     XSNOWB,XMAXB
        BNE     L810
        JMP     L1000
L810:   MOV     YMINB,R0
        DEC     R0
        ASR     R0
        ASR     R0
        ASR     R0
        MOV     R0,BEGBYT
        MOV     YMAXB,R1
        DEC     R1
        ASR     R1
        ASR     R1
        ASR     R1
        MOV     R1,ENDBYT
        ADD     #PLTBUF+1,R0
        ADD     #PLTBUF-1,R1
L900:   CMP     R0,R1
        BHI     L905
        MOVB    #125,(R0)+
        BR      L900
L905:   MOV     BEGBYT,R0
        ASL     R0
        ASL     R0
        ASL     R0
        NEG     R0
        ADD     YMINB,R0
        ASR     R0
        MOV     #125,R2
        TST     R0
        BLE     L915
L910:   ASR     R2
        ASR     R2
        SUB     #1,R0
        BGT     L910
L915:   MOV     BEGBYT,R3
        ADD     #PLTBUF,R3
        BISB    R2,(R3)
L920:   MOV     ENDBYT,R0
        INC     R0
        ASL     R0
        ASL     R0
        ASL     R0
        INC     R0
        SUB     YMAXB,R0
        ASR     R0
        MOV     #125,R2
        TST     R0
        BLE     L940
L930:   ASL     R2
        ASL     R2
        SUB     #1,R0
        BGT     L930
L940:   MOV     ENDBYT,R3
        ADD     #PLTBUF,R3
        BISB    R2,(R3)
L1000:  MOV     #ALST1,R5
        JSR     PC,VCNGT
        RTS     PC
ALST1:  .BYTE   6,0
        .WORD   XAGRID,XANDB,XADDB,XTYPE,XAING,XANGB
        .END