title: 'smoothstep' : no matching overloaded function found
body: <p>I am going through the <a href="https://thebookofshaders.com/07/" rel="nofollow noreferrer">Book of Shaders tutorial</a> on GLSL and I attempt to use the <code>smoothstep</code> function but I get this error. You can see it happen when I changed the <code>step</code> to the <code>smoothstep</code> function below.</p>
  
  <pre><code>// 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);
  }
  </code></pre>
  
  <p>Any ideas how to fix this?</p>