Along with setting a version for macOS to use instead of 2.1,
most if not all Essentials games require a maximum texture size
of at least 16384x16384. OpenGL 4.1 requires this as a minimum.
Don't globally set float precision to mediump, only fragment
shaders need that and defining it for vertex shaders causes
tilemap cracks.
Also manually define low precision for variables that hold
color / alpha values.
