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93 lines
2.5 KiB
Markdown
93 lines
2.5 KiB
Markdown
dual playfield
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==============
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[hardware reference link](http://amigadev.elowar.com/read/ADCD_2.1/Hardware_Manual_guide/node0078.html)
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We now try and set up a dual playfield screen with 3 bitplanes per playfield. This gives us 7 colors + transparent for each playfield.
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Set the number of bitplanes per playfield in [constants.i](constants.i)
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```
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SCREEN_BIT_DEPTH equ 3 ; 3 bitplanes per playfield
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```
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New copper list that assigns bitplanes to each playfield after poking in [dual_playfield_mode.s](dual_playfield_mode.s)
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```
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copper:
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pf1_bitplanepointers:
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;; this is where bitplanes are assigned to playfields
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;; http://amigadev.elowar.com/read/ADCD_2.1/Hardware_Manual_guide/node0079.html
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;; 3 bitplanes per playfield, playfield1 gets bitplanes 1,3,5
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dc.w BPL1PTL,0
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dc.w BPL1PTH,0
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dc.w BPL3PTL,0
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dc.w BPL3PTH,0
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dc.w BPL5PTL,0
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dc.w BPL5PTH,0
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pf2_bitplanepointers:
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;; 3 bitplanes per playfield, playfield2 gets bitplanes 2,4,6
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dc.w BPL2PTL,0
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dc.w BPL2PTH,0
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dc.w BPL4PTL,0
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dc.w BPL4PTH,0
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dc.w BPL6PTL,0
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dc.w BPL6PTH,0
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dc.l $fffffffe
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```
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Poke the copper list with the bitplane pointer addresses in [init.s](init.s):
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```
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;; poke playfield 1 bitplane pointers
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lea pf1_bitplanepointers(pc),a0
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lea pf1_bitplanes(pc),a1
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bsr.s pokeBitplanePointers
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;; poke playfield 2 bitplane pointers
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lea pf2_bitplanepointers(pc),a0
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lea pf2_bitplanes(pc),a1
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bsr.s pokeBitplanePointers
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```
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Enable 2x the bitplanes, set the DBLPF bit in BPLCON0 to enable dual playfields. Optionally re-order the playfields with PF2PRI in BPLCON2. See [init.s](init.s):
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```
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;; enable 2x the bitplanes as 2x playfields
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move.w #((SCREEN_BIT_DEPTH*2)<<12)|COLOR_ON|DBLPF,BPLCON0(a6)
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;; set playfield2 to have priority
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move.w #PF2PRI, BPLCON2(a6)
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```
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try it
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------
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* [Download disk image](bin/dual_playfield_mode.adf?raw=true)
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* <a href="http://alpine9000.github.io/ScriptedAmigaEmulator/#amiga_examples/dual_playfield_mode.adf" target="_blank">Run in SAE</a>
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Screenshots:
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playfield 1
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-----------
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playfield 2
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-----------
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dual playfields, playfield 2 in front
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-------------------------------------
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```
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move.w #PF2PRI, BPLCON2(a6)
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```
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dual playfields, playfield 1 in front
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-------------------------------------
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```
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move.w #0, BPLCON2(a6)
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```
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