SKShader to create parallax background
<p>A parallax background with a fixed camera is easy to do, but since i'm making a topdown view 2D space exploration game, I figured that having a single SKSpriteNode filling the screen and being a child of my SKCameraNode and using a SKShader to draw a parallax starfield would be easier.</p>

<p>I went on shadertoy and found this simple looking shader.  I adapted it successfully on shadertoy to accept a vec2() for the velocity of the movement that I want to pass as an SKAttribute so it can follow the movement of my ship.</p>

<p>Here is the original source:
<a href="https://www.shadertoy.com/view/XtjSDh" rel="noreferrer">https://www.shadertoy.com/view/XtjSDh</a></p>

<p>I managed to make the conversion of the original code so it compiles without any error, but nothing shows up on the screen.  I tried the individual functions and they do work to generate a fixed image.</p>

<p>Any pointers to make it work?</p>

<p>Thanks!</p>