So since that Shader Editor came out, we got rid of the old noise effect and implemented a way fancier post process effect -- which of I cant be arsed to talk more, you´ll see when you eventually play Scintilla.
But! But but..
Since every second Source modder out there is interested in having noise on their screen, without coding, and multiple people have harassed me on how to do that, I figured I´d save some time and write it here. What you need to know is generally how to work with .vmt files or create new textures. Nothing fancy, the basics will do.
TRICKERY! Noise screen overlay:
1. Make a texture file, .vtf, with pure noise into it. 1024x1024 will do, preferably with DXT1 compression..
2. The vmt file for this noise would be something along the lines of..
3. In the Hammer editor, have a Logic_Auto in your level, and in the properties, OnSpawn triggers a env_screenoverlay, and that screenoverlay is assigned on the noise texture of yours.
4. ..And thats it! When you start the level, it´ll wrap your noisy texture across the screen.
You most likely have to adjust the noise´s intensity alot. I used a VERY VERY dim texture for mine, basically it was like dark grey and black. I think one way to make the material dimmer would be via vmt code, "$color" "[0.5 0.5 0.5]" would cut half out of all the colour channels. Should work. Otherwise, just make the texture itself darker. Takes a bit of experimenting.
AND, you can have multiple frames in the .vtf ---this grows the texture´s size alot, so be wary-- and then use a AnimatedTexture proxy. In the above vmt example I used a proxy that makes the texture scroll crazy fast.. but in-game I had both the scrolling and 2 frame animation active. It did the trick, noise looked smooth.
...and finally, if you dont know how to use proxies, check this out, superhandy.
So yeh, simple, but might come in handy for some modders.