'smoothstep' : no matching overloaded function found

Question

I am going through the Book of Shaders tutorial on GLSL and I attempt to use the smoothstep function but I get this error. You can see it happen when I changed the step to the smoothstep function below.

// Author @patriciogv - 2015
// http://patriciogonzalezvivo.com

#ifdef GL_ES
precision mediump float;
#endif

uniform vec2 u_resolution;
uniform vec2 u_mouse;
uniform float u_time;

void main(){
    vec2 st = gl_FragCoord.xy/u_resolution.xy;
    vec3 color = vec3(0.0);

    // bottom-left
    vec2 bl = smoothstep(vec2(0.1),st); 
    float pct = bl.x * bl.y;

    // top-right 
    // vec2 tr = step(vec2(0.1),1.0-st);
    // pct *= tr.x * tr.y;

    color = vec3(pct);

    gl_FragColor = vec4(color,1.0);
}

Any ideas how to fix this?

Answer 1

step and smootstep are 2 functions with a different signature and behavior. While step generates a hard transition from 0 to 1 at an edge, smoothstep smoothly interpolates between 2 values.

As specified in the Khronos reference, smoothstep has 3 parameters:

genType smoothstep( genType edge0, genType edge1, genType x );

• edge0 Specifies the value of the lower edge of the Hermite function.
• edge1 Specifies the value of the upper edge of the Hermite function.
• x Specifies the source value for interpolation.

smoothstep performs smooth Hermite interpolation between 0 and 1 when edge0 < x < edge1. This is useful in cases where a threshold function with a smooth transition is desired.

In comparison, step has 2 parameters:

genType step( genType edge, genType x);

• edge Specifies the location of the edge of the step function.
• x Specify the value to be used to generate the step function.

step generates a step function by comparing x to edge.
For element i of the return value, 0.0 is returned if x[i] < edge[i], and 1.0 is returned otherwise.