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Old 10 March 2019, 14:26   #1
DanScott
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Displaying hardware sprites to the left of DDFSTART

Was there a method that allows this ? If there is, I forget what it was

Can anyone shed some light on this please
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Old 10 March 2019, 14:36   #2
ross
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Quote:
Originally Posted by DanScott View Post
Was there a method that allows this ? If there is, I forget what it was

Can anyone shed some light on this please
Write with copper on some early line position to BPL1DAT.
Ah, and change DIWSTRT.

Cheers
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Old 10 March 2019, 14:46   #3
DanScott
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Ah cheers, that worked... write to BLP1DAT forces output of all other BPLxDAT too, so DIW can hide that
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Old 10 March 2019, 14:57   #4
Toni Wilen
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Note also possible side-effects:

I think ECS Denise ignores BPL1DAT write if it is done too early. OCS Denise allows it very early horizontally. (Or it was the opposite?) I am not sure if I tested this fully.

Also because BPL1DAT write enables Denise bitplane shifters, it can add hidden BPLCON1 offset. Same side-effect as "unaligned" DDFSTRT does.
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Old 10 March 2019, 15:00   #5
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Ah cheers, that worked... write to BLP1DAT forces output of all other BPLxDAT too, so DIW can hide that
But DIW cover also the sprite...

Well, you can use a sprite to cover also the glitch

EDIT:
Or set DDFSTOP one word more for zeroed contents
(in fact it depends on whether you have scroll or other factors what is best to do)

Last edited by ross; 10 March 2019 at 15:10.
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Old 10 March 2019, 15:18   #6
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Also because BPL1DAT write enables Denise bitplane shifters, it can add hidden BPLCON1 offset. Same side-effect as "unaligned" DDFSTRT does.
I'm not entirely sure I understand the consequences of this ...
in any case the shift is also applied when loading the subsequent bitplane data through DMA.

So only if you change BPLCON1 dynamically on the line I guess there can be undesidered effect, right?
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Old 10 March 2019, 15:24   #7
Toni Wilen
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I'm not entirely sure I understand the consequences of this ...
in any case the shift is also applied when loading the subsequent bitplane data through DMA.

So only if you change BPLCON1 dynamically on the line I guess there can be undesidered effect, right?
It is non-issue, I remembered wrong. Next DMA BPL1DAT will "reset" it.
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Old 10 March 2019, 15:42   #8
DanScott
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Quote:
Originally Posted by ross View Post
But DIW cover also the sprite...

Well, you can use a sprite to cover also the glitch

EDIT:
Or set DDFSTOP one word more for zeroed contents
(in fact it depends on whether you have scroll or other factors what is best to do)

I have a 32 byte wide screen centralised, and needed to display 32 pixel wide sprites to the left and right of this (as a border). So I've changed DIWSTART to hide the bitplane showing from setting BPL1DAT, but not to hide the sprite
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Old 10 March 2019, 16:00   #9
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Quote:
Originally Posted by Toni Wilen View Post
It is non-issue, I remembered wrong. Next DMA BPL1DAT will "reset" it.
Ok



Quote:
Originally Posted by DanScott View Post
I have a 32 byte wide screen centralised, and needed to display 32 pixel wide sprites to the left and right of this (as a border). So I've changed DIWSTART to hide the bitplane showing from setting BPL1DAT, but not to hide the sprite

Have fun!
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Old 10 March 2019, 17:58   #10
DanScott
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Have fun!
Always
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Old 10 March 2019, 20:16   #11
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Quote:
Originally Posted by DanScott View Post
I have a 32 byte wide screen centralised, and needed to display 32 pixel wide sprites to the left and right of this (as a border). So I've changed DIWSTART to hide the bitplane showing from setting BPL1DAT, but not to hide the sprite
I never realized this was possible, neat trick and not too Copper-expensive apparently.
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Old 10 March 2019, 20:24   #12
Toni Wilen
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32 pixel wide sprites
2x16 or really 32 pixel wide? If 32 pixel (=AGA), just set the border sprite bit and don't bother with BPL1DAT
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Old 10 March 2019, 20:37   #13
DanScott
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2x16 (OCS/ECS)
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