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Explain this glitch in Battle Toads?
http://forums.nesdev.com/viewtopic.php?f=2&t=16932
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Author:  psycopathicteen [ Fri Jan 12, 2018 4:39 pm ]
Post subject:  Explain this glitch in Battle Toads?

https://www.youtube.com/watch?v=U34vUdSIBtE

This guy is playing PAL games on NTSC systems, and I can understand most of the glitches, but why is the HUD showing up on top of the BG? Is this some kind of CRT problem?

Author:  pubby [ Fri Jan 12, 2018 4:42 pm ]
Post subject:  Re: Explain this glitch in Battle Toads?

HUD is sprites and unaffected by PAL/NTSC timings. Black bar is cycle-timed and affected by PAL's longer VBLANK.

Author:  tokumaru [ Fri Jan 12, 2018 4:44 pm ]
Post subject:  Re: Explain this glitch in Battle Toads?

That HUD is way too big to be made out of sprites.

Author:  psycopathicteen [ Fri Jan 12, 2018 4:54 pm ]
Post subject:  Re: Explain this glitch in Battle Toads?

I'm guessing that Battle Toads might be flickering between showing the gameplay, and showing just the HUD and a black screen, and the camera doesn't pick up the brightness difference.

Author:  lidnariq [ Fri Jan 12, 2018 5:12 pm ]
Post subject:  Re: Explain this glitch in Battle Toads?

psycopathicteen wrote:
I'm guessing that Battle Toads might be flickering between showing the gameplay, and showing just the HUD and a black screen, and the camera doesn't pick up the brightness difference.
Quickly loading the PAL ROM in FCEU-0.98 and emulating as NTSC shows that's exactly what's going on.

The PAL build seems to spend enough time that the game logic is only evaluated every other vblank when run at 30kcy/vblank instead of 33kcy/vblank. And relatedly, after it misses a real vblank, the status bar is is delayed by an extra 16 scanlines.

Author:  psycopathicteen [ Fri Jan 12, 2018 7:36 pm ]
Post subject:  Re: Explain this glitch in Battle Toads?

lidnariq wrote:
psycopathicteen wrote:
I'm guessing that Battle Toads might be flickering between showing the gameplay, and showing just the HUD and a black screen, and the camera doesn't pick up the brightness difference.
Quickly loading the PAL ROM in FCEU-0.98 and emulating as NTSC shows that's exactly what's going on.

The PAL build seems to spend enough time that the game logic is only evaluated every other vblank when run at 30kcy/vblank instead of 33kcy/vblank. And relatedly, after it misses a real vblank, the status bar is is delayed by an extra 16 scanlines.


So does that mean it is flickering?

Author:  lidnariq [ Fri Jan 12, 2018 7:58 pm ]
Post subject:  Re: Explain this glitch in Battle Toads?

Yes.

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