In this episode, I discuss how to use `gl_Position.w` to draw fog.
Fog factor = (end point - distance from eye point) / (end point - starting point)
Where starting point less than distance from eye point less than end point
if fog factor == 1, then object is completely shown; if fog factor == 0, object completely hidden
fragment color = surface color * fog factor + fog color * (1-fog factor)