函数图像:

float Circle(vec2 uv,vec2 center,float r,float blur){
    //相当于uv坐标到中心的距离
    float d = length(uv - center);
    float c = smoothstep(r,r - blur,d);
    return c;
}

float Band(float t,float start,float end,float blur)
{
    float step1 = smoothstep(start - blur,start + blur,t);
    float step2 = smoothstep(end + blur,end - blur,t);
    return step1 * step2;
}

float Rect(vec2 uv,float left,float right,float bottom,float top,float blur)
{
    float band1 = Band(uv.x,left,right,blur);
    float band2 = Band(uv.y,bottom,top,blur);
    return band1 * band2;
}

void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    // Normalized pixel coordinates (from 0 to 1)
    vec2 uv = fragCoord/iResolution.xy;
    uv -= 0.5;
    //将uv的x坐标进行放大
    uv.x *= iResolution.x / iResolution.y;

    float mask = 0.0;
    float x = uv.x;
    float m = (x + 0.5) * (x - 0.5);
    m = m * m * 5.0;
    float y =  uv.y + m;

    mask = Rect(vec2(x,y),-0.5 ,0.5,-0.1,0.1,0.02);

    vec3 col = vec3(1,1,0) * mask;
    fragColor = vec4(col,1.0);
}