three.js-examples | Bower package only containing the JavaScript files | Script Programming library

I'm basically trying to achieve a kaleidoscopic effect with just one side, but I'm working with lots of Points, so I'd like that to happen in the shader. However if there's a Threejs trick that mirrors half of the texture or the Points object, that would be great. I tried to apply transformation matrices but I can't get it to work.

I found an old KaleidoShader that requires the usage of EffectComposer, but I'd like to implement it manually myself (without EffectComposer) and I'm struggling to do so. I'm using an FBO and I tried adding the code from that shader in both my simulation and render shaders but it's having no effect at all. Do I have to add yet another FBO texture or is it possibile to do those calculations in one of the existing shaders?

For visual reference https://ma-hub.imgix.net/wp-images/2019/01/23205110/premiere-pro-mirror-effect.jpg

I've spent so much time without getting to the bottom of this, hopefully someone can point me in the right direction.

Thanks