Forming A Dual-Playfield Display - Commodore Amiga Hardware Reference Manual

VLOOP: MOVE.W
VLl:
AND.W
BEQ
MOVE.W
MOVE.W
BPL
MOVE.L
BRA
MOVE.L
BRA
; Character list
INTREQR(AO),DO
#$0020,DO
VLOOP
#$0020,INTREQ(AO)
VPOSR(AO),DO
VLl
#$20000,BPLIPTH(AO)
VLOOP
#$20050,BPLIPTH(AO)
VLOOP
;Read interrupt requests
jMask off all but vertical blank
jLoop until vertical blank comes
jReset vertical interrupt
jRead LOF bit into
DO
bit 15
jlf LOF
=
0, jump
;LOF
=
1, point to $20000
;Back to top
;LOF
=
0, point to $20050
;Back to top
DC.L $18FC3DFO,$3C6666D8,$3C66COCC,$667CCOCC
DC.L $7E66COCC,$C36666D8,$C3FC3DFO,$OOOOOOOO
DC.L $FFFFFFFF
Forming a Dual-playfield Display
For more flexibility in designing your background display, you can specify two playfields
instead of one. In dual-playfield mode, one play field is displayed directly in front of the
other. For example, a computer game display might have some action going on in one
playfield in the background, while the other playfield is showing a control panel in the
foreground. You can then change either the foreground or the background without hav-
ing to redesign the entire display. You can also move the two playfields independently.
A dual-playfield display is similar to a single-playfield display, differing only in these
aspects:
o Each play field in a dual display is formed from one, two or three bit-planes.
o The colors in each playfield (up to seven plus transparent) are taken from
different sets of color registers.
o You must set a bit to activate dual-playfield mode.
58 Play field Hardware