; file car.asm ; .INCLUDE 'ATARI.IS' leftkey equ "7" rightkey equ "9" stopkey equ "8" carwidth equ 14 carheight equ 12 scroll: movem.l d1-d4/a0/a1/a6,-(sp) ;save the CPU registers used label: lea.l label(pc),a6 ;all addresses in the program .BASE 6,label ;are relative to label. The ; GFA ASSEMBLER will automatically ; convert them. move.l screen,d0 ;Is screen position ; already defined (<> -1)? bpl redraw ;yes, then scroll etc... firsttime: Physbase ; first call: ; Where is screen? move.l d0,screen ;note for later use move.w 7*4+4(sp),d0 ;fetch parameters move.w d0,pos ;set start position bsr drawcar ;draw car bra done ;and finished. redraw: Vsync ;wait for frame flyback move.w pos,d0 ;then erase the old car bsr drawcar movea.l screen,a1 ;screen start address to a1 move.w 7*4+4(sp),d0 ;fetch parameter line number mulu.w #80,d0 ;convert to bytes (Lines*80) lea.l 0(a1,d0.w),a0 ;load a1+d0 to a0 neg.l d0 ;-d0+32000 is block length addi.l #32000,d0 bsr qcopy ;call subroutine qcopy here Crawio #$000000ff ;read keyboard, ASCII code to d0.b move.w vx,d1 ;hold horizontal speed move.w pos,d2 ;and position ready in registers cmpi.b #leftkey,d0 ;acceleration to the left? bne .tstright ; no subq.w #1,d1 ; yes, vx := vx-1 bra .finished ; and key read .tstright: cmpi.b #rightkey,d0 ;not left, then ;perhaps right? bne .tststop ; no, then perhaps ; stop? addq.w #1,d1 ; yes, vx := vx+1 bra .finished ; and key read .tststop: cmpi.b #stopkey,d0 ;Key for abrupt stop? bne .finished ; no, then finished moveq.l #0,d1 ; yes, vx := 0 .finished: add.w d1,d2 ;Position = position + speed bpl .tstleft ; >= 0, not beyond left border moveq.l #0,d1 ; <0: position to left border and moveq.l #0,d2 ; set speed to 0 bra .savnpos ; remember new position .tstleft: cmpi.w #640-carwidth,d2 ; >=640-carwidth? bcs .savnpos ; no, position is okay move.w #640-carwidth,d2 ; yes, then position to right ; border and moveq.l #0,d1 ; speed to 0 .savnpos: move.w d1,vx ;Note new position and speed move.w d2,pos Vsync ;Wait again for frame flyback move.w d2,d0 ; and draw car at new position bsr drawcar ;any collision sets d0<>0 done: movem.l (sp)+,d1-d4/a1/a2/a6 ;restore registers rts ;d0 holds result ; ; drawcar ; ; Input: d0 -- Line position of the car in pixels ; Output: d0 -- <> 0, if car leaves road ; ; registers changed: 01234567 ; D:------- ; A-------- ; ; Road is ScrnMem Bit = 1 ; Ditch and obstacle ScrnMem Bit = 0 ; drawcar: movem.l d1-d4/a0/a1,-(sp) moveq.l #15,d1 ;shift and.w d0,d1 lsr.w #4,d0 ;word offset add.w d0,d0 movea.l screen,a1 ;pointer to first word under car lea.l 30*80(a1),a1 adda.w d0,a1 lea.l car,a0 ;pointer car table moveq.l #carheight-1,d2 ;line pointer moveq.l #0,d3 ;erase collision flags .carloop: moveq.l #0,d4 ;erase long word move.w (a0)+,d4 ;and write carmask to low word ror.l d1,d4 ;rotate carmask move.w (a1),d0 ;left word under car not.w d0 ;test for collision and.w d4,d0 or.w d0,d3 ;note any collisions eor.w d4,(a1)+ ;put car onto road/erase swap.w d4 ;the same for the second word move.w (a1),d0 not.w d0 and.w d4,d0 or.w d0,d3 eor.w d4,(a1) lea.l 78(a1),a1 dbf d2,.carloop move.l d3,d0 ;copy collision status to d0 movem.l (sp)+,d1-d4/a0/a1 ;and return rts pos: .DC.w 0 ;car start position vx: .DC.w 0 ; screen: .DC.l -1 ; car: .DC.w %1111000000111100 ;mask for car: maximum width 16 .DC.w %1111111111111100 ;maximum height is freely selectable .DC.w %1111111111111100 ; constants .DC.w %0001111111110000 ; car width and .DC.w %0001111111110000 ; car height have to be adapted. .DC.w %0000111111100000 .DC.w %0000011111000000 .DC.w %0000001110000000 .DC.w %0000011111000000 .DC.w %0000011111000000 .DC.w %0000001110000000 .DC.w %0000000100000000 ;========================================================================== ; ;qcopy Quick copy of a memory block ; ; ; Input: ; a0: Address of source block ; a1: Address of destination block ; d0: Length of block in bytes (0<= Length <= 3,145,727) ; d0 is not checked for correct length! ; ; Output: ; a0,a1: Point to byte behind relevant block ; ; registers changed: ; D 1,2,3,4,5,6,7 ; A 2,3,4,5,6,7 qcopy: movem.l d1-d7/a2-a6,-(sp) ;save registers move.w a0,d1 ;check orientation of blocks move.w a1,d2 ; different ==>copy bytes andi.w #1,d1 ; both odd ==>one byte, then ,as if odd andi.w #1,d2 ; both even copy blocks eor.w d1,d2 bne .copybytes tst.w d1 beq .copyeven .copyodd: move.b (a0)+,(a1)+ ;odd address: copy one byte subq.w #1,d0 ;adapt counter beq .done ;and test for end .copyeven: divu.w #12*4,d0 ;even address: copy blocks of 48 bytes bra .vlcpy ;downward loop .vlloop: movem.l (a0)+,d1-d7/a2-a6 ;Loop transfers 48 bytes at a time movem.l d1-d7/a2-a6,(a1) ;Simulates writing with lea.l 12*4(a1),a1 ;postincrement .vlcpy: dbf d0,.vlloop ; swap.w d0 ;look at remainder of division ext.l d0 ;extend to whole register ror.l #2,d0 ;division by 4, remainder in bit 30,31 bra .lcpy ;downward loop .lloop: move.l (a0)+,(a1)+ ;counter div 4 copy longs .lcpy: dbf d0,.lloop .word: lsl.l #1,d0 ; Is remainder a word? bcc .byte ; no, then perhaps byte move.w (a0)+,(a1)+ ; yes, then copy word .byte: tst.l d0 ; Is remainder byte? bpl .done ; no, then finished move.b (a0)+,(a1)+ ; yes, then copy it bra .done ; ; Blocks are of different orientation, so byte access is used. ; Optimisation not worth the effort as case too rare. ; .copybytes: bra .btst ; move memory block in bytes, as otherwise .bloop: move.b (a0)+,(a1)+ ; an address error occurs .btst: dbf d0,.bloop ; here loop lower word swap.w d0 ; look at higher part subq.w #1,d0 ; also decrement bcs .done ; <0, then finished swap.w d0 ; else: restore order bra .bloop ; and repeat inner loop .done: movem.l (sp)+,d1-d7/a2-a6 ; finished. rts ; then back.