int isvarying(<type>x)
int isvarying(<type>x[])
Returns 1 when the given variable is varying, or 0 when it is uniform. A
variable is varying when it may have a different value for each processor
in the VEX SIMD array. If a value is varying, shader execution will
generally be slower - so this function can be useful when debugging shader
performance. Any variable type can be passed to the isvarying()
function.