Can a USR command damage a ZX Spectrum?

Re:Can a USR command damage a ZX Spectrum? by ksaj on Monday December 16, 2019 @04:40AM (#21801914)

The weird thing I remember with Hercules cards was that their memory was square even if the display wasn't. In other words, if your screen was 720x350, you could set up X for 720x720 and scroll down past the bottom edge of the screen to expose a bigger area than fits on the visible part of the screen.

I assume it's still the same on all graphics boards today, but I haven't seen this bidirectional desktop scrolling since back in the Hercules days.

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Re:Can a USR command damage a ZX Spectrum? by newnewpdro on Monday December 16, 2019 @04:50PM (#21807657)

I never had a Hercules, but that virtual desktop automatic panning was a general feature of XFree86. It was especially useful back then when we had CRTs capable of myriad native video modes.

In XFree86 you'd switch through them with ctrl-alt-+ and ctrl-alt--, the monitor's video mode would change but the virtual desktop size stayed the same. Whenever the monitor showed less than the entire virtual desktop, the viewport would pan within the virtual desktop when the pointer moved past the screen edges.

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Re:Can a USR command damage a ZX Spectrum? by ksaj on Wednesday December 18, 2019 @03:12PM (#21828891)

Yup exactly. I think most people didn't realize if they set X for a square screen, they could scroll all over the place. I'd forgotten that it was called a viewport.

And of course, my favourite was all the custom/customizable video modes that Hercules had silently lurking on the board. Some of the early 32-bit desktops (like the 32032) used 4-colour Hercules at 1024x1024. I don't think 16 and 8 bit PeeCees were capable of going that far, though.

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