1.sin函数

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 r = length(uv) * 2.0;
    float a = atan(uv.y,uv.x);
    float f = sin(a * 1.0);
    float c = smoothstep(f,f + 0.02,r);
    fragColor = vec4(vec3(f),1.0);
}

效果:

2.周期缩小

float f = sin(a * 2.0);

效果:

float f = sin(a * 3.0);

效果:

3.加上距离判断

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 r = length(uv) * 2.0;
    float a = atan(uv.y,uv.x);
    float f = sin(a * 3.0);
    float c = smoothstep(f,f + 0.02,r);
    fragColor = vec4(vec3(c),1.0);
}

效果: