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Last updated on Oct-18-2019 Download

Emulator Display Issue

Emulator Display Issue
by on (#185051)
Hi there !

Newcomer here.

I've been working on an emulator for some time now and so far things were going pretty well. I got at the point where most things work but ... some don't :'(. (These debug NES roms are awesome by the way <3).
So that's it, I'm stuck. I'm having some... Display issues and scrolls issues on some games and really can't figure out what is happening. I've been lurking in the wiki, forum looking for someone who already stumbled upon this problem but no luck :/

My emulator passes every CPU tests I could find with the exception of a BRK test that fails. It also seems I have a few minor issues related to clock timing (some tests still don't pass) but I do not think it would cause these kind of problems ?

I've attached a few screenshots that show what is happening.

On the first, it's a scroll issue I'm having on Castlevania where the screen displays black stripes when scrolling.
The second is Zelda where I have a 8 pixel offset (My Link 'walks' on the background)
The third is also a Zelda screenshot, when I hit start the starts menu does not go away

That's it :) I don't want to bother you guys much but if someone has an idea, I welcome it!

Thank you for your time ! And thank you for this awesome website \o/
Re: Emulator Display Issue
by on (#185199)
Auto answering my own questions if anyone has (one day) the same kind of issues I had:

- The Castlevania scroll issue and the Zelda offset were due to me not prefetching enough tiles for the background to render (This was a great help https://wiki.nesdev.com/w/images/d/d1/Ntsc_timing.png), so there was a mismatch between the rendered tiles and hori(v)
- The Zelda issues were due to my nametable mirrors, I wasn't properly reading where I was supposed to