Oldschool effects using shaders

You can implement more or less anything with GLSL shaders; if you want ready-made cool examples you should ask for something more specific, while if you want to reproduce something oldschool it is a straightforward reverse engineering and reimplementation task.

I don't know what you mean by "post effects", but you might find the shader-based simulation of CRT behaviour in emulators like MAME and Stella interesting.

What kind of "cool post effects" are you looking for?

What kind of "cool post effects" are you looking for?

Plasma effect, for example

Plasma effect, for example

Plasma effect is pretty trivial, it is basically a simple trigonometric (I think? can't remember what formula it is) warping of a two-dimensional space. In GLSL this would essentially translate to:
- reading the pixel coordinate for each pixel
- warping it according to the plasma formula
- reading the framebuffer at the new pixel coordinate
- write the resulting pixel to the original coordinates

One could add multisampling on top of that to avoid pixel loss and shearing due to the uneven gradient of the distortion field, but it wouldn't be oldschool anymore would it!