1.fract函数代码

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 x = uv.x * 2.0;
    //将x限制在0-1内
    //float m = min(fract(x),fract(1.0 - x));
    float m = fract(x);
    float c = smoothstep(0.0,0.1,m - uv.y);

    fragColor = vec4(vec3(c),1.0);
}

效果:

2.极坐标

void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    // Normalized pixel coordinates (from 0 to 1)
    vec2 uv = (fragCoord.xy - 0.5 * iResolution.xy) / iResolution.y;
    vec2 st = vec2(atan(uv.x,uv.y),length(uv));
    //将坐标变换到极坐标
    uv = st;
    float x = uv.x * 5.0;
    float m = min(fract(x),fract(1.0 - x));
    float c = smoothstep(0.0,0.1,m * 0.3  + 0.2 - uv.y);

    fragColor = vec4(vec3(c),1.0);
}

旋转坐标

void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    // Normalized pixel coordinates (from 0 to 1)
    vec2 uv = (fragCoord.xy - 0.5 * iResolution.xy) / iResolution.y;
    vec2 st = vec2(atan(uv.x,uv.y),length(uv));
    //将坐标变换到极坐标
    uv = vec2(st.x / 6.2831 + 0.5 + iTime * 0.2,st.y);
    float x = uv.x * 5.0;
    float m = min(fract(x),fract(1.0 - x));
    float c = smoothstep(0.0,0.1,m * 0.5  + 0.2 - uv.y);

    fragColor = vec4(vec3(c),1.0);
}

效果: