A lot of folks like to apply a pincushion/curvature effect to their emulator image to try and capture a bit of the old CRT TV curved tube effect. This can be a problem, though, when paired with a scanline effect, since the curvature introduces an aliasing artifact on the scanlines known as a "moire pattern":
|This is a worst-case scenario, used for illustrative purposes.|
Notice the ugly pattern fanning out from the middle of the outside edges of the screen
Graphics programmer Timothy Lottes (author of the popular FXAA algorithm and a lovely public domain CRT shader, among others) was working on ways of dealing with the aliasing/moire problem for VR and published this shadertoy showing how to hide it by introducing jitter/noise in where the texture is sampled. Turns out that same strategy can be used to mitigate our scanline moire.
When applied to an actual game image, this:
When curvature is added to an existing, normally flat CRT shader (Themaister's crtglow-gaussian shader, one of my favorites), we go from this:
Here's the code snippet that does it (all copyrights belong to Mr. Lottes):
This code can be added to many CRT shaders by wrapping the shader's fragment texcoord declaration with the moire_resolve() function to add the jitter/noise and then wrapping that with the Warp() function to add the curvature. You can see an example of where I've done exactly that in the crtglow-gaussian shader here to create the screenshots above.