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hoglet67 / RGBtoHDMI

Bare-metal Raspberry Pi project that provides pixel-perfect sampling of Retro Computer RGB/YUV video and conversion to HDMI
GNU General Public License v3.0
849 stars 115 forks source link

Auto delay adjust for 1280x1024 monitors #81

Open IanSB opened 5 years ago

IanSB commented 5 years ago

You can still buy 1280x1024 monitors (unlike 1600x1200) and they seem to be quite common. They are closer to 4:3 than current widescreen monitors and should be ideal for the beeb as integer scaling from 640x256 is straightforward. However each mode on the BBC has a different horizontal position so you either have to capture more than 640 pixels which eliminates simple integer scaling or manually adjust the delay after each mode change. Maybe some sort of automatic adjustment could be implemented. This issue also affects PCs where the text and graphics versions of the same resolution have different offsets due to the character ROM delay. I have seen this sort of auto adjustment on LCD monitors following a mode change when the image moves left and right by a few pixels but the main issue with the BBC is detecting the mode change as there isn't always going to be a sync disturbance. It might have to be an auto adjust triggered by one of the configurable buttons.

hoglet67 commented 5 years ago

Wouldn't this require some sort of a calibration screen that ensured the first column of pixels we being used?

On a modern PC it's less of an issue, because the background is rarely black.

IanSB commented 5 years ago

Wouldn't this require some sort of a calibration screen

Potentially but most non-text output on the beeb is games and quite a lot have non-black backgrounds. Worst case it's a completely manual adjustment using the configurable buttons.

IanSB commented 5 years ago

Maybe continuously capture 8 or 16 pixels on each side of the active 640 pixels and as soon as any non-zero pixel is detected in those areas, adjust the delay so that those pixels are in the visible area. Might be visually annoying when it shifts but it shouldn't happen that often.