Resetting The Address Pointers; Sprite Display Example - Commodore Amiga Hardware Reference Manual

RESETTING THE ADDRESS POINTERS
For one single display field, the system will automatically read the data structure and
produce the sprite on-screen in the colors that are specified in the sprite's color registers.
If you want the sprite to be displayed in subsequent display fields, you must rewrite the
contents of the sprite pointers during each vertical blanking interval. This is necessary
because during the display field, the pointers are incremented to point to the data which
is being fetched as the screen display progresses.
The rewrite becomes part of the vertical blanking routine, which can be handled by
instructions in the Copper lists.
SPRITE DISPLAY EXAMPLE
This example displays the
~paceship
sprite at location V
=
65, H
=
128. The equates
are the usual, so they're not repeated here.
; First, we set up a single bit-plane.
LEA CUSTOM,AO
MOVE.W #$1200,BPLCONO(AO)
MOVE.W #$OOOO,BPLIMOD(AO)
MOVE.W #$0000,BPLCON1(AO)
MOVE.W #$0024,BPLCON2(AO)
MOVE.W #$0038,DDFSTRT(AO)
MOVE.W #$OODO,DDFSTOP(AO)
MOVE. W #$2C81,DIWSTRT(AO)
MOVE.W #$F4Cl,DIWSTOP(AO)
j
Set up color registers.
,
MOVE.W #$0008,COLOROO(AO)
MOVE.\V #$OOOO,COLOR01(AO)
MOVE.W #$OFFO,COLOR17(AO)
MOVE.W #$OOFF ,COLOR18(AO)
MOVE.W #$OFOF,COLOR19(AO)
; Move Copper list to $20000.
MOVE.L #$20000,A1
LEA COPPERL,A2
106 Sprite Hardware
jPoint AO at custom chips
i1 bit-plane color is on
iModulo
=
0
iHorizontal scroll value
=
0
iSprites have priority over playfields
iSet data-fetch start
iSet data-fetch stop
iSet display window start
iSet display window stop
iBackground color
=
dark blue
iForeground color
=
black
i Color 17
=
yellow
iColor 18
=
cyan
iColor 19
=
magenta
iPoint A1 at Copper list destination
iPoint A2 at Copper list source