[2018] Procedural Skybox Shader in GameMaker (GLSL ES)

Project:

 A procedural skybox shader I made in GameMaker while I've been super into graphics programming

The only geometry in the scene is a cube around the camera. Everything else is shader math. 

Loosely based on the default Unity skybox, though it's probably faster to pre-render the skybox, especially for reflection maps. 

This is maybe going to be included in the v2 of my Skybox Converter (It maps a 2D Horiztonal-Repeating texture into a rather convincing skybox)