; ; Bitplane Example 10. ; ; Written for OZAmiga by Chris Leathley. ; ; use the hi-res picture and display it on a lo-res screen, scrolling ; it from side to side. ; ; this display changes the data fetch start position half way down the ; screen to illistrate how the HSCROLL register upsets a normal display ; ; ; Branch offsets into the Amiga's rom kernal librarys (exec) ; Forbid = -132 ; turn off Multitasking Permit = -138 ; turn it back on again CloseLibrary = -414 ; open a library (from ram or disk) OpenLibrary = -552 ; close an opened library ; -------------------------------------------------------------------------- ; a68k code ; SECTION code,CODE,CHIP ; make sure in chip memory ; devpac code SECTION code,CODE_C ; make sure in chip memory ; -------------------------------------------------------------------------- ; program starts here ; START: clr.l $0 ; clear address 0 move.l $4,a6 ; turn off multitasking jsr Forbid(a6) ; ; set up bitplane address into copper list program before copper is ; turned on ; move.l #PICTURE,d0 ; move "ADDRESS" of picture ; into d0 (longword) move.w d0,BP1LO+2 ; store bottom q6 bits into ; copperlist. $00E2l0 ; we use +2 to skip the first ;`word (ie $00E2) and put the ; data in the "0" word swap d0 ; swap upper 16 bits with ; lower 16 bits in d0. move.w d0,BP1HI+2 ; store upper 16 bits ; fire up the copper ; .wait_vb cmp.b #$FF,$00DFF006 ; wait for vb to change bne.s .wait_vb move.l #COPPERLIST,$00DFF080 ; insert new copperlist move.w #$8380,$00DFF096 ; use new control bits ; (turn on copper & bitplane dma) ; wait for user to press the left mouse button and then exit program ; MAIN_LOOP: cmp.b #$FF,$00DFF006 ; wait for vertical blank bne.s MAIN_LOOP bsr SCROLL_WARNING ; put in our little delay otherwise the scroll code will execute ; many times while the raster line is still on postion $FF move.w #256,d0 ; count down from 256 to 0 .delay sub.w #1,d0 bne .delay btst #$06,$00BFE001 ; left mouse button ? bne.s MAIN_LOOP ; no? do it all again ; program finished, exit back to dos ; EXIT: move.l $4,a6 ; exec pointer lea GFX_NAME,a1 ; library name moveq #0,d0 ; library version jsr OpenLibrary(a6) ; open graphics library move.l d0,a1 ; d0 has pointer to library move.l $0026(a1),$00DFF080 ; restore original copperlist jsr CloseLibrary(a6) ; close graphics library jsr Permit(a6) ; turn back on multitasking moveq #0,d0 ; no errors rts ; return of amiga dos ; -------------------------------------------------------------------------- ; ; scroll warning bitmap (640 pixels wide) left and right in lo-res ; (displaying only 320 pixels at a time) ; SCROLL_WARNING: tst.w SCROLL_DIRECTION ; test direction flag bne .right ; 0 = left, 1 = right .left sub.w #1,SCROLL_VALUE ; subtract 1 from x position tst.w SCROLL_VALUE ; are we at 0 yet? bne .set move.w #1,SCROLL_DIRECTION ; yes so now go right bra .set .right add.w #1,SCROLL_VALUE cmp.w #320,SCROLL_VALUE ; at max right position ; the bitplane width is 640 ; pixels but since we are ; allready displaying 320 ; pixels we only need to scroll ; the difference (320) bne .set move.w #0,SCROLL_DIRECTION ; now go left .set move.l #0,d0 move.w SCROLL_VALUE,d0 ; get x scroll value move.l d0,d1 ; move to a temporary regisiter divu #16,d1 ; calculate number of "words" ; into bitplane pointers mulu #2,d1 ; convert result from bytes ; to "words". (bitplane pointers ; must be a EVEN address) not.b d0 ; invert scroll offset and.w #$000F,d0 ; clip offset to range ($0 - $F) move.w d0,d2 ; move to temp reg. lsl.w #4,d2 ; shift scroll value 4 bits to ; the left ($xF -> $F0) or.w d2,d0 ; mix ODD and EVEN scroll values move.w d0,HSCROLL_COP+2 ; put result into copperlist move.l #PICTURE,d0 ; base address of picture add.l d1,d0 ; add number of "words" onto ; picture start address. move.w d0,BP1LO+2 ; set bitplane pointers swap d0 move.w d0,BP1HI+2 rts SCROLL_DIRECTION dc.w 1 ; (start going right) SCROLL_VALUE dc.w 0 ; -------------------------------------------------------------------------- ; graphics library name ; GFX_NAME: dc.b 'graphics.library',0 EVEN ; ; our copperlist program ; COPPERLIST: dc.w $0180,$0000 ; screen starts off black dc.w $0120,0,$0122,0 ; don't worry about this just dc.w $0124,0,$0126,0 ; yet as all it does is set dc.w $0128,0,$012A,0 ; all sprite positions to zero dc.w $012C,0,$012E,0 ; so no wondering sprites dc.w $0130,0,$0132,0 ; appear on the screen dc.w $0134,0,$0136,0 dc.w $0138,0,$013A,0 dc.w $013C,0,$013E,0 BP1HI dc.w $00E0,0 ; bitplane 1 address pointers BP1LO dc.w $00E2,0 dc.w $100,$1200 ; turn on 1 bitplane (lo-res) HSCROLL_COP dc.w $102,0 ; hardware scroll to be zero dc.w $104,0 ; bitplane - sprite priority dc.w $08E,$2C81 ; window start (top left) dc.w $090,$2CC1 ; window stop (bottom right) ; (STANDARD PAL DISPLAY VALUES) dc.w $092,$30 ; bitplane DMA start (16 bits ; early) dc.w $094,$d0 ; bitplane DMA stop dc.w $108,40-2 ; odd modulo (adjusted for early ; data fetch start) dc.w $10A,40-2 ; even modulo dc.w $182,$FF0 ; colour 1 = yellow dc.w $2B09,$FFFE,$180,$F00 ; red line dc.w $2C09,$FFFE,$180,$000 ; screen back to black ; ; set the data fetch back to normal value (must also set bitplane modulos) ; this will show you how the HSCROLL regisiter, shifts the picture out ; to the left (dosn't look very nice) ; dc.w $A409,$FFFE,$180,$005 ; blue background dc.w $092,$38 ; bitplane DMA start dc.w $108,40 ; odd modulo dc.w $10A,40 ; even modulo dc.w $FFDF,$FFFE ; skip NTSC vertical blank dc.w $2C09,$FFFE,$180,$F00 ; another red line dc.w $2D09,$FFFE,$180,$000 dc.w $FFFF,$FFFE ; end of copper list ; start vertical blank ; -------------------------------------------------------------------------- ; ; include raw picture data into assembly code ; PICTURE: INCBIN oz.warning.raw ; -------------------------------------------------------------------------- END ; end of program