What does `precision mediump float` mean?
This determines how much precision the GPU uses when calculating floats. highp is high precision, and of course more intensive than mediump (medium precision) and lowp (low precision).
Some systems do not support highp at all, which will cause code not to work at all on those systems.
On systems that DO support highp, you will see a performance hit, and should use mediump and lowp wherever possible. A good rule of thumb that I saw was:
- highp for vertex positions,
- mediump for texture coordinates,
- lowp for colors.
Hope that helps!