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MiSTer-devel / ZX-Spectrum_MISTer

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Missing border lines in Pentagon mode #44

Open Bricabrac-Spam opened 1 year ago

Bricabrac-Spam commented 1 year ago

Hello,

I'd like to bring to your attention an out of spec behaviour of Pentagon mode whereby it does not render at least 16 lines of top border. This can be clearly observed in "Across the Edge" demo where at some point a text "ACROSS" is drawn on top of the screen and "EDGE" at the bottom and that top part is cut. Also, ZX Next core in "Soviet timings" personality renders noticably higher top border than bottom.

I don't know if that was an intentional decision to implement it like that in ZX Spectrum core but I would like to kindly ask to make the missing lines to appear as it would in real Pentagon.

Thank you very much in advance.

sorgelig commented 1 year ago

Hmm.. i need to check. Border size i choose to let more paper space on screen. I will see.

Bricabrac-Spam commented 1 year ago

Thank you for looking into this.

Yes, I fully understand the point. Most of the users won't even notice that some lines are missing. But if core is mostly used for watching demoscene then in some specific cases this small discrepancy from the real hardware becomes apparent.

So if there was a possibility to add a toggle in the menu to turn on/off additional lines similarily as there is an option to make border smaller, then I guess everyone would be happy.

Many thanks.

sorgelig commented 1 year ago

I've checked youtube. I've noticed insanely large borders. No way it was like that back in 80x-90x. This is not how CRT was looking. It seems demo is written for emulator. CRT couldn't show as much border as it's shown on video. Also video has flickering everywhere. They use effect of more colors which is handled by unreal emulator but quite distracting if you see it n real HW. Also i've noticed upper word ACROSS isn't right. Probably something wrong with timings. Not sure how it will work on real HW. Unreal emulator goes too far emulating what wasn't in real HW.

sorgelig commented 1 year ago

upd: i was wrong about word ACROSS. It looks ok. Just half out of sight..

Bricabrac-Spam commented 1 year ago

If I am correct this video is from the authors of the demo: https://www.youtube.com/watch?v=b-kkzl2foaQ It is a no-flick version so for sure was captured on emulator. However, I have to confirm that it looks exactly the same on my MiSTer hooked up to Sony BVM CRT monitor (except the flickery but it is still manageable). The border size is realy this big. Only the top part is missing some lines. Regarding the CRT TVs of the 80' and 90' they are known of severe overscan. Because of that, back then when you hooked up your Pentagon or regular ZX Spectrum to a consumer TV or even monitor, the border looked significantly smaller than on the video or emulator. But even then more expensive TVs which had service menu allowed for geometry adjustments and by that eliminating overscan and even achieve underscan. Both my Sony CRT TV from mid 90' also display big border from the ZX Spectrum core on MiSTer.

For some unknow reason Pentagon is different in terms of border than regular Spectrum (maybe becuse of that unusual 48.8Hz refresh rate?). It has less lines on the bottom part than a Spectrum (49 instead of 57) and more on top (65 instead of 49). Effectively it is like 'paper' area is a little bit out of centre to the bottom part comaparing to Spectrum. Overall Pentagon displays just 8 lines more than ZX Spectrum and such number of lines can still be easily handled by any reasonable CRT. Please see this webpage for more details about Pentagon specifics vs. Spectrum: https://wiki.specnext.dev/Reference_machines Hope this site is accurate.

Unfortunatelly I don't have a real Pentagon so I cannot check how the real hardware would present when connected to my monitor. Having a Pentagon has been my dream since year 1999 when I get to know about Speccy demoscene, but here in my place finding one is simply impossible. MiSTer with its ZX Spectrum core is my "close as it can only be" alternative to real hardware.

I fully understand your hesitation to implement those additional border lines especially if it is hard to do. Yes, only the handfull of demos that are heavy on border effects would show the difference. But if it wouldn't be hard to implement then I think an option in the menu to turn on/off additional lines would not hurt anyone.

Whatever you decide I am still greatfull you have looked into this.