Extract the sign of the parameter
float sign(float x)
vec2 sign(vec2 x)
vec3 sign(vec3 x)
vec4 sign(vec4 x)
x
specify the value from which to extract the sign.
sign()
returns -1.0 if x is less than 0.0, 0.0 if x is equal to 0.0, and +1.0 if x is greater than 0.0.