Amiga Screens: A Primer

weinzierl an hour ago | parent | next [-]

How do different resolutions (pixel sizes) work? I get that everything memory related (including color mode and depth) could be switched on a raster line.

In theory it should be possible to change the frequency of the video signal mid screen as well, but I have a hard time to imagine switching repeatedly every frame wouldn't have driven the monitors of the time crazy. Even multi-sync monitors needed probably a couple of frames to sync, right?

	▲	noone_youknow 9 minutes ago \| parent \| next [-]
		In the context of the Amiga you didn’t need to change the signal frequency, the underlying video signal stayed the same. For wider pixels, the hardware just drew each pixel for longer, and for taller pixels each pixel spanned more lines. Pixels weren’t real in the CRT days :)
	▲	fredoralive 13 minutes ago \| parent \| prev [-]
		It’s basically just an SD TV signal, the vertical height in lines doesn’t change, it largely just swaps if each line outputs 320 or 640 pixels during its assigned time period. Having interlaced and non interlaced modes at once seems a bit funky though, but I assume it just forces everything into interlaced with the non interlaced mode sections having the same line sent on both fields?

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LastTrain 33 minutes ago | parent | prev | next [-]

I don’t know much about Amiga, but from this article I recognize the Atari 8 bit / ANTIC DLI heritage at play!

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MiroslavPokorny 3 hours ago | parent | prev [-]

Maybe its me, but i believe the primary or secondary reason for screen is different screens had different resolutions and color depths, both of which dont really exist these days on any major OS.

	▲	summa_tech 2 hours ago \| parent \| next [-]
		It feels like the concept faded with the advent of large VRAM and fast fill rate graphics accelerators. I remember old X Window System workstations supporting multiple concurrent windows with different color depths and modes. The hardware would compose windows from memory during display scan-out, all to save VRAM.
	▲	vidarh 2 hours ago \| parent \| prev [-]
		I've been thinking a lot about this. Virtual desktops gets us somewhat close, but not quite. You're right the difference in resolution and colour depth isn't really relevant any more. What I think made screens feel different was as a grouping mechanism, usually driven by a single application (though in more recent versions of AmigaOS you could open "public screens") that would manage the layout for that screen. You can do that with virtual desktops, but it takes some effort to simulate the behaviour. I'm slowly iterating on something like that for my wm. I now snapshot the (by default tiling) layout and restore it, letting me "open" and "close" screens/virtual desktops, and re-open the applications on them, so instead of opening a single application that opens a screen, I will open a "project" and it will open a desktop and multiple applications on it whose windows will snap into place. I'm not happy with it yet, but it feels somewhat closer to me to how it felt to use Amiga screens.