Describe the feature you would like to be added to the shader.

I really love this shaderpack, but I think it could really use a customizable barrel distortion slider then I'd be satisfied.

For reference, here's a couple of images as to what it looks like in videogames. The image basically gets distorted a little outwards from the center in a spherical shape; lines near the edges of the screens will be curved rather than straight. Of course, some of these images may look extremely distorted, but that's why I asked to make it a slider.
(courtesy of some quick Google Images searches)

Teardown (slight barrel distortion)

Minecraft (edited screenshot with GIMP just to show the effect)

Also if you do decide to add this feature in, maybe keep the default setting for it to off, because it will look jarring for some other users.