You have to adapt the Shadertoy code provided (the fragment shader) and also you have to modify the xml header of the jitter shader file (which extension is.jxs) and the vertex shader of said file in order to work properly within the jit.gl.slab object. Then, in the fragment part of the shader you have to adapt the main() function as well. In regards to function names, you can keep the names as it is, or change them. The tutorial has a very detailed walkthrough on how to do those things.