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Old 06 March 2020, 21:16   #1
mcgeezer
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Sprite priorities without dual playfield on AGA

This is probably a stupid question but I'll ask it anyway - despite me testing this.

Is it possible to use sprite priorities without dual playfield mode on AGA?

The HRM states "PF2P2-PF2P0, bits 5-3 are the priority bits for normal (non-dial) playfields", is it possible to overide this so the desired result would be a mashup of bitplanes with the sprite data...

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Old 10 March 2020, 23:56   #2
roondar
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I missed out on this one. It should be possible, I know that for OCS such things generally work even when Dual Playfield mode is disabled and I see no reason why it wouldn't be the same for AGA. the standard priority settings for a single playfield OCS screen where sprites are on top of the bitplanes is BPLCON2=$24, which sets both playfields to be on top. IIRC, setting this value differently on OCS does change the behaviour of sprites vs playfields even if not in Dual Playfield mode. I see no reason why AGA would do this differently.

Haven't recently tested it though...

Edit: that didn't come out quite the way I meant to...

Last edited by roondar; 11 March 2020 at 00:16.
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Old 11 March 2020, 00:41   #3
DanScott
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BPLCON2=$24 is for sprites in front of playfields (the usual desired behaviour)

Yes, I am sure AGA works the same. If dual playfield is not enabled, then only the playfield 1 bits are used.
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Old 11 March 2020, 00:46   #4
mcgeezer
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I tried the shit out of this and couldnt get it to budge.

Sprites were either on top or behind the playfield.

Might take another look though.
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Old 11 March 2020, 01:03   #5
DanScott
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Yeah, sprites will be either in front or behind... they won't be a "mashup" of bitplanes. There's no bitplane bits in the priority bits.. only sprite pairs and playfield bits
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Old 11 March 2020, 01:05   #6
Antiriad_UK
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I'm doing a routine at the moment which is single playfield and OCS and the HW ref manual matches up and you have to use the PF2 values. I've got the sprites flipping priority on various conditions. I would ass-u-me it's the same on AGA. Code has segments like this:

Code:
	move.w	#$0000,P0_CL_BPLCON2_OFFSET+2(a1)	;PF->SPR0->SPR2->SPR4
	move.w	#$0008,P0_CL_BPLCON2_OFFSET+2(a1)	;SPR0->PF->SPR2->SPR4
	move.w	#$0010,P0_CL_BPLCON2_OFFSET+2(a1)	;SPR0->SPR2->PF->SPR4
	move.w	#$0018,P0_CL_BPLCON2_OFFSET+2(a1)	;SPR0->SPR2->SPR4->PF
Edit: Like Dan says, it's all or nothing. Either in front of all bitplanes or behind all.
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Old 11 March 2020, 01:08   #7
roondar
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Right, it’s clear now I misremembered. Still, good to have the correct info out here.
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