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KONEY · 07 September 2021, 20:00

I'm trying to scroll a portion of a plane vertically using blitter, so far I have no problem going up but as soon as I change direction I'm getting some unexplicable (for me!) results.

This routine is executed at every frame. Source and destination match, the shift is obtained by adding the size of a line to the source (A3) so the image moves up 1px every frame. 1 is also subtracted from H so the size of operation don't mess with next bitplane.

As long as SCROLL_DIR_Y=0 the scroll works OK and when it's 1 the size of a line is added to the destination (A4) instead, to obtain the opposite direction. But as soon as this is triggered the result of the blit is as in second image, without any scrolling in-between.

Using modulos of 0 and scrolling the whole area have the same results.

I'm obviously missing something, maybe an expert eye can give me a hint?

Code:

__SCROLL_BG_Y:
    MOVEM.L    D0-A6,-(SP)    ; SAVE TO STACK
    BTST.B    #6,DMACONR    ; for compatibility
    MOVE.W    #%0000100111110000,BLTCON0

    ; ## MAIN BLIT ####
    MOVE.L    BGPLANE0,A3
    MOVE.L    BGPLANE0,A4

    MOVE.B    SCROLL_DIR_Y,D5
    TST.B    D5
    BEQ.S    .goUp
    ADD.L    #336/16*2,A4        ; POSITION Y
    BRA.S    .goBlit
    .goUp:
    ADD.L    #336/16*2,A3        ; POSITION Y
    .goBlit:

    bsr    WaitBlitter
    MOVE.W    #$FFFF,BLTAFWM        ; BLTAFWM
    MOVE.W    #$FFFF,BLTALWM        ; BLTALWM
    MOVE.W    #%0000000000000000,BLTCON1    ; BLTCON1
    MOVE.W    #bpl-wblit,BLTAMOD        ; BLTAMOD
    MOVE.W    #bpl-wblit,BLTDMOD        ; BLTDMOD

    MOVE.L    A3,BLTAPTH        ; BLTAPT SRC
    MOVE.L    A4,BLTDPTH        ; DESC
    MOVE.W    #(h-1)*64+160/16,BLTSIZE    ; BLTSIZE
    ; ## MAIN BLIT ####

    MOVEM.L    (SP)+,D0-A6    ; FETCH FROM STACK
     RTS

Going up OK:

Going down:

07 September 2021, 20:00	#1
KONEY OctaMED Music Composer Join Date: Jan 2009 Location: Venice - Italy Age: 49 Posts: 670	HELP with blitter vertical shift I'm trying to scroll a portion of a plane vertically using blitter, so far I have no problem going up but as soon as I change direction I'm getting some unexplicable (for me!) results. This routine is executed at every frame. Source and destination match, the shift is obtained by adding the size of a line to the source (A3) so the image moves up 1px every frame. 1 is also subtracted from H so the size of operation don't mess with next bitplane. As long as SCROLL_DIR_Y=0 the scroll works OK and when it's 1 the size of a line is added to the destination (A4) instead, to obtain the opposite direction. But as soon as this is triggered the result of the blit is as in second image, without any scrolling in-between. Using modulos of 0 and scrolling the whole area have the same results. I'm obviously missing something, maybe an expert eye can give me a hint? Code: __SCROLL_BG_Y: MOVEM.L D0-A6,-(SP) ; SAVE TO STACK BTST.B #6,DMACONR ; for compatibility MOVE.W #%0000100111110000,BLTCON0 ; ## MAIN BLIT #### MOVE.L BGPLANE0,A3 MOVE.L BGPLANE0,A4 MOVE.B SCROLL_DIR_Y,D5 TST.B D5 BEQ.S .goUp ADD.L #336/162,A4 ; POSITION Y BRA.S .goBlit .goUp: ADD.L #336/162,A3 ; POSITION Y .goBlit: bsr WaitBlitter MOVE.W #$FFFF,BLTAFWM ; BLTAFWM MOVE.W #$FFFF,BLTALWM ; BLTALWM MOVE.W #%0000000000000000,BLTCON1 ; BLTCON1 MOVE.W #bpl-wblit,BLTAMOD ; BLTAMOD MOVE.W #bpl-wblit,BLTDMOD ; BLTDMOD MOVE.L A3,BLTAPTH ; BLTAPT SRC MOVE.L A4,BLTDPTH ; DESC MOVE.W #(h-1)*64+160/16,BLTSIZE ; BLTSIZE ; ## MAIN BLIT #### MOVEM.L (SP)+,D0-A6 ; FETCH FROM STACK RTS Going up OK: Going down: Attached Thumbnails