1.代码

#define PI 3.14159265358979323846

vec2 rotate2D(vec2 _st, float _angle)
{
    _st -= 0.5;
    _st =
    mat2(cos(_angle),-sin(_angle),
    sin(_angle),cos(_angle)) * _st;
    _st += 0.5;
    return _st;
}

vec2 tile(vec2 _st, float _zoom){
    _st *= _zoom;
    return fract(_st);
}

float box(vec2 _st, vec2 _size, float _smoothEdges){
    _size = vec2(0.5)-_size*0.5;
    vec2 aa = vec2(_smoothEdges*0.5);
    vec2 uv = smoothstep(_size,_size+aa,_st);
    uv *= smoothstep(_size,_size+aa,vec2(1.0)-_st);
    return uv.x*uv.y;
}

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;
    vec3 color = vec3(0.0);
    // Divide the space in 4
    uv = tile(uv,4.);
    // Use a matrix to rotate the space 45 degrees
    uv = rotate2D(uv,PI*0.25);
    // Draw a square
    color = vec3(box(uv,vec2(0.7),0.01));
    // color = vec3(st,0.0);


    fragColor = vec4(color,1.0);
}

效果: