dual playfield

We now try and set up a dual playfield screen with 3 bitplanes per playfield. This gives us 7 colors + transparent for each playfield.

Set the number of bitplanes per playfield in [constants.i](constants.i]

SCREEN_BIT_DEPTH	equ 3   ; 3 bitplanes per playfield

New copper list that assigns bitplanes to each playfield after poking in [dual_playfield_mode.s](dual_playfield_mod.s]

copper:
pf1_bitplanepointers:
  ;; this is where bitplanes are assigned to playfields
  ;; http://amigadev.elowar.com/read/ADCD_2.1/Hardware_Manual_guide/node0079.html
  ;; 3 bitplanes per playfield, playfield1 gets bitplanes 1,3,5
  dc.w	BPL1PTL,0
  dc.w	BPL1PTH,0
  dc.w	BPL3PTL,0
  dc.w	BPL3PTH,0
  dc.w	BPL5PTL,0
  dc.w	BPL5PTH,0
pf2_bitplanepointers:
  ;; 3 bitplanes per playfield, playfield2 gets bitplanes 2,4,6
  dc.w	BPL2PTL,0
  dc.w	BPL2PTH,0
  dc.w	BPL4PTL,0
  dc.w	BPL4PTH,0
  dc.w	BPL6PTL,0
  dc.w	BPL6PTH,0
  dc.l	$fffffffe

Poke the copper list with the bitplane pointer addresses:

  ;; poke playfield 1 bitplane pointers
  lea	pf1_bitplanepointers(pc),a0
  lea	pf1_bitplanes(pc),a1
  bsr.s	pokeBitplanePointers

  ;; poke playfield 2 bitplane pointers
  lea	pf2_bitplanepointers(pc),a0
  lea	pf2_bitplanes(pc),a1
  bsr.s	pokeBitplanePointers

Enable 2x the bitplanes, and optionally re-order the bitplanes:

  ;; enable 2x the bitplanes as 2x playfields
  move.w	#((SCREEN_BIT_DEPTH*2)<<12)|COLOR_ON|DBLPF,BPLCON0(a6)
  ;; set playfield2 to have priority
  move.w	#PF2PRI, BPLCON2(a6)

README.md

dual playfield

try it

playfield 1

playfield 2

dual playfields, playfield 2 in front

dual playfields, playfield 1 in front