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Old 05 April 2018, 15:39   #1
Old_Bob
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Hardware Sprite Glitch

I've noticed an odd bit of weirdness with one of the sprites in my Bomb Jack game...



There are two halves, more or less, of different sets of sprite data visible, as well as some rogue pixels. Strangely, it only occurs at a certain, narrow band of scanlines in the frame and displays correctly above and below. The problem also seems to be absent when emulating AGA.

Looking in the debugger, the sprite pointer registers appear to be correct and the data looks right in Chip RAM. I can't test it on real hardware so I don't know if it's a problem with my program or, possibly, a bug in WinUAE?


B

Last edited by Old_Bob; 05 April 2018 at 17:59.
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Old 05 April 2018, 16:50   #2
Toni Wilen
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If it only happens in OCS: most likely Agnus bug where bitplane DMA also eats second word of previous sprite. (http://eab.abime.net/showpost.php?p=1196166&postcount=4)
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Old 05 April 2018, 18:53   #3
Old_Bob
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Thanks, dude.

After some testing using the quickstart configs, it's both OCS and ECS that exhibit the behaviour. It seems to manifest itself slightly differently, though, when emulating a 500, 500+ or 600. The A3000 quickstart option doesn't seem to be working for me here, using 3.6.1.

All the other hardware sprites on screen are fine. Only the B coin, which uses sprites 4 and 5 in attached mode is affected.


B
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Old 05 April 2018, 20:32   #4
Toni Wilen
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Include statefile that shows the problem, preferably something that shows the glitch longer than few frames
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Old 06 April 2018, 00:53   #5
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No need, dude.

It turns out that the routine that updates that sprite was occasionally being called at just the time the data was getting read during the frame.

Moving a single JSR cured it.

Thanks, again.


B
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