thebookofshaders/11/noise-move.frag

// Author @patriciogv - 2015
// http://patriciogonzalezvivo.com

#ifdef GL_ES
precision mediump float;
#endif

uniform vec2 u_resolution;
uniform vec2 u_mouse;
uniform float u_time;

float random (in float _x) {
    return fract(sin(_x)*1e4);
}

// Based on Morgan McGuire @morgan3d
// https://www.shadertoy.com/view/4dS3Wd
float noise (in float _x) {
    float i = floor(_x);
    float f = fract(_x);
    float u = f * f * (3.0 - 2.0 * f);
    return mix(random(i), random(i + 1.0), u);
}

float box(in vec2 _st, in vec2 _size){
    _size = vec2(0.5) - _size*0.5;
    vec2 uv = smoothstep(_size,
                        _size+vec2(0.001),
                        _st);
    uv *= smoothstep(_size,
                    _size+vec2(0.001),
                    vec2(1.0)-_st);
    return uv.x*uv.y;
}

float cross(in vec2 _st, float _size){
    return  box(_st, vec2(_size,_size/4.)) + 
            box(_st, vec2(_size/4.,_size));
}

void main(){
    vec2 st = gl_FragCoord.xy/u_resolution.xy;
    vec3 color = vec3(0.0);
        
    // To move the cross we move the space
    vec2 translate = vec2(cos(noise(u_time)*3.1415*2.0),
                          sin(noise(u_time)*3.1415*2.0));
    st += translate*0.35;

    // Show the coordinates of the space on the background
    // color = vec3(st.x,st.y,0.0);

    // Add the shape on the foreground
    color += vec3(cross(st,0.25));

    gl_FragColor = vec4(color,1.0);
}