1.圆环

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;
    //到(0.0,0.0)的距离
    float d = length(uv);
    float c = fract(d * 10.0);
    fragColor = vec4(vec3(c),1.0);
}

效果:

2.四象限

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;
    //到(0.3,0.3)的距离
    float d = length(abs(uv) - 0.3);
    float c = fract(d * 10.0);
    fragColor = vec4(vec3(c),1.0);
}

效果: