[seanhunter]

Game Devs have always done amazing things like this.

I remember my one and only real attempt at game dev involved the zx spectrum where I got a book from my local library with all sorts of inspiring tricks in it. For people who don't know/remember, the speccy used to output to a TV[1] but didn't have enough graphics juice to actually fill the screen, so you could render into a pane in the center of the screen and the only thing you could do with the outside border was you could set the color [2]. Anyhow, this spectrum game dev book showed how to build a flight simulator game in assembly and one of the incredible hacks they employed was to change the color of the border at exactly the right moments in the scan path of the CRT so it would look like you had a continuous horizon all the way to the edges of the screen. You couldn't actually render any graphics out there but it blew my mind that you could at least make the sky and land stretch right to the edge of the screen.

[1] Which would have been CRT at the time, which turns out to be important for this hack.

[2] You can see this border here. It's the ugly green box. All spectrum games used to have this. https://forums.libretro.com/uploads/default/original/3X/c/9/...

[circuit10]

These kinds of tricks were also very common on the NES, to create things like a HUD that doesn't scroll with the rest of the screen by changing the scroll values at the right time. Eventually they even started putting hardware in the cartridge to assist this by interrupting the CPU at the right time

[tuukkah]

Amiga may have taken this furthest with Copper, a co-processor that was synced with the CRT signal and programmed in a DSL for timed changes of register values in the other chips: https://en.wikipedia.org/wiki/Amiga_Original_Chip_Set#Copper