Example/Dynamically Uniform Expression

This example code shows what are and are not dynamically uniform expressions.

in vec3 fromPrevious;
in uvec2 fromRange;

const int foo = 5;
const uvec2 range = uvec2(2, 5);
uniform vec2 pairs;

uniform sampler2d tex;

void main()
{
  foo; // constant expressions are dynamically uniform.
  
  uint value = 21; // 'value' is dynamically uniform.
  value = range.x; // still dynamically uniform.
  value = range.y + fromRange.y; // not dynamically uniform; current contents come from a non-dynamically uniform source.
  value = 4; // dynamically uniform again.
  if (fromPrevious.y < 3.14)
    value = 12;
  value; // NOT dynamically uniform. Current contents depend on 'fromPrevious', an input variable.

  float number = abs(pairs.x); // 'number' is dynamically uniform.
  number = sin(pairs.y); // still dynamically uniform.
  number = cos(fromPrevious.x); // not dynamically uniform.

  vec4 colors = texture(tex, pairs.xy); // dynamically uniform, even though it comes from a texture.
                                        // It uses the same texture coordinate, thus getting the same texel every time.
  colors = texture(tex, fromPrevious.xy); // not dynamically uniform.

  for(int i = range.x; i < range.y; ++i)
  {
       // loop initialized with, compared against, and incremented by dynamically uniform expressions.
    i; // Therefore, 'i' is dynamically uniform, even though it changes.
  }

  for(int i = fromRange.x; i < fromRange.y; ++i)
  {
    i; // 'i' is not dynamically uniform; 'fromRange' is not dynamically uniform.
  }
}