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Old 03 October 2019, 01:12   #15
Per aspera ad astra

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Join Date: Mar 2017
Location: Crossing the Rubicon
Age: 49
Posts: 2,367
Originally Posted by mydma View Post
But am I right in understanding here that because BPL0DAT is written at the start of a raster line, then writing to SPR0DATA will show the sprite even though bitplane dma is disabled?

The first write activate sprites for the full line (actually it's called BPL1DAT).
Warning, cannot be done too soon.

I had already tried writing $ffff to SPR0DATA at the top of the frame with sprite dma disabled to cause a vertical bar but it obviously only showed where bitplane dma was actually enabled.
Is the write to BPL1DAT (DMA, Copper, even CPU) that activate the buffered output for all the bplanes. At the fine position specified in BPLCON1.
Also a non-aligned DDFSTRT join the equation, especially in fetch modes higher than OCS/ECS (your $24 is one of these special cases.. try to change BPLCON1 ).
This can open you to very interesting effects (the famous BPLCON1 zoom trick to do an hw line shrink).

EDIT: gosh, just noticed that Dan is in this thread, ask him for BPLCON1 trick
First effect (~25"):
[ Show youtube player ]

Last edited by ross; 03 October 2019 at 01:45.
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