Stupid smiley face shadertoy shader

smiley.frag

float circle(vec2 uv, vec2 p, float r, float blur)
{
    return smoothstep( r, r-blur, length(uv - p) );
}


void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    
    vec2 uv = ( fragCoord.xy / iResolution.xy ) - .5f;
    vec2 pos = ( iMouse.xy / iResolution.xy ) - .5f;
    
    float ratio = iResolution.x/iResolution.y;
    uv.x *= ratio;
    pos.x *= ratio;
    
    float mask = circle(uv, pos, .4f, .01f);
    mask -= circle(uv, pos + vec2(.15f, .1f), .09f, .01f);
    mask -= circle(uv, pos + vec2(-.15f, .1f), .09f, .01f);

    float mouth = circle(uv, pos, .3f, .01f);
    mouth -= circle(uv, pos + vec2(0.f, 0.1f), .3f, .01f);
    mouth = clamp(mouth, 0.f, 1.f);
    mask -= mouth;
    
    const vec3 color = vec3(1.f, 1.f, 0.f);
    fragColor = vec4(mask * color, 1.0f);
}