Search notes:

OpenGL ES Shading Language

It seems that the «ES» stands for Embedded Subset.

Apparently, the OpenGL ES Shading Language is a (strict?) subset of the OpenGL Shading Language.

int vs float

42 is an integer, not a float. The following assignment produces the error Cannot convert from const int to highp float.

float num = 42;

Thus, in order to assign a number to a float, it must be made sure that a float is assigned:

float num = 42.0;

const float PI = radians(180.0);