Though I don't really understand how an image is produced on a CRT. In this circuit (https://www.falstad.com/pong/net.html), what is "NET" actually connected to?
The best set of videos explain how hardware can display video is in Ben eater site. It assumes VGA.
https://eater.net/vga
I don't what monitor type was assumed in this design but a similar approach could create a classic NTSC signal into a TV.
Here is a solution with a micro controller http://eyetap.org/ece385/lab5.htm
A CRT moves the electron beam direction from top-to-bottom, left-to-right. If it sends electrons, the corresponding position on the screen lights up for about 1/50 s. So you can encode your pixels as a 0/1 pulse train, although you do have to take care of the time it takes to move the beam to the next line, and at the end to reset it to the top.
On another page[1], you can spot NET being OR'd together with PAD1 and PAD2 to VIDEO. I would guess that it's abstracted away on this page for simplicity.
I think it's PFM. I'm not seeing anything in the simulator that lets you add a CRT type of display.
[Edit] Yeah, this is the case. If you view the page source, there's some custom JS drawing "NET" to a canvas. It's hard coded to pull from specific wires when they cross certain voltage thresholds in the simulation.
[Edit2] The implementation is also very buggy. The CRT simulation is just looping through X&Y completely decoupled from the circuit sim. Simple operations like stopping and running the sim while changing simulation speed will cause it to get off.
I believe it is connected to the little red line you can see if you slow the simulation down. When it is high, the head of the little red line draws a pixel. Otherwise, it doesn't.
You can check this by deleting the input to net and then connecting a wire from some slow moving signal to net (so you can see how it responds in the image).
The CRT itself isn't actually modeled of course -- it is external hardware.
Though I don't really understand how an image is produced on a CRT. In this circuit (https://www.falstad.com/pong/net.html), what is "NET" actually connected to?