1.smoothstep(a,b,v), a < b

#define PI 3.1415926

vec2 fixUV(in vec2 uv){
    return 3.0 * (2.0 * uv - iResolution.xy) / 
           min(iResolution.x,iResolution.y);
}

vec3 grid(in vec2 uv){
    vec3 color = vec3(0.4);
    vec2 grid = floor(mod(uv,2.0));
    if(grid.x == grid.y){
        color = vec3(0.6);
    }
    float fx = smoothstep(1.1 * fwidth(uv.x),fwidth(uv.x),abs(uv.x));
    color = mix(color,vec3(0.0),fx);
    float fy = smoothstep(1.1 * fwidth(uv.y),fwidth(uv.y),abs(uv.y));
    color = mix(color,vec3(0.0),fy);
    return color;
}

float func(float x){
    return smoothstep(-1.0,1.0,x);
}

float plotFunc(vec2 uv){
    float f = func(uv.x);
    return smoothstep(f - 0.01,f + 0.01,uv.y);
}

void mainImage(out vec4 fragColor,in vec2 fragCoord){
    vec2 uv = fixUV(fragCoord);
    vec3 color = grid(uv);
    float count = 0.0;
    for(int i = 0;i < 4;i++){
        for(int j = 0;j < 4;j++){
            vec2 offset = vec2(float(i),float(j)) - 1.0;
            count += plotFunc(fixUV(fragCoord + offset));         
        }
    }
    if(count > 8.0){
        count = 16.0 - count;
    }
    count = count * 2.0 / 16.0;
    color = mix(color,vec3(1.0),vec3(count));
    fragColor = vec4(color,1.0);
}

效果图:

由图可知，smoothstep(a,b,v), a < b时，表示，v[HTML_REMOVED]b 时返回1

2.smoothstep(a,b,v), a > b

float func(float x){
    return smoothstep(1.0,-1.0,x);
}

效果:

由图可知，smoothstep(a,b,v), a > b时，表示，v[HTML_REMOVED]a 时返回0

3.step

float func(float x){
    return step(1.0,x);
}

效果图:

由图可知，小于1时直接返回0，大于1时直接返回1，没有中间过渡。