tshader

float val(vec2 p)
{
    return step(length(p-vec2(0.2,0.7)), 0.2);
    //return texture(iChannel0, src).r;
}

float GetTh(vec2 src, float sz)
{
    float p = val(src);
    float pul = val(src + vec2(-sz, sz));
    float pur = val(src + vec2( sz, sz));
    float dnl = val(src + vec2(-sz,-sz));
    float dnr = val(src + vec2( sz,-sz));
    
    return max(max(abs(pul-p), abs(pur-p)), max(abs(dnl-p), abs(dnr-p)));
}
void mainImage(out vec4 fragColor, in vec2 fragCoord)
{
    vec2 uv = fragCoord/iResolution.xy;// * vec2(1.,iResolution.y/iResolution.x);
	vec3 col = vec3(0.0);
    
    //for(int i = 0;i<6;i++)
    int i = 5;
    {
        float s = float(i);
        float d = 1./(s+1.);
        float sz = 0.5 / pow(2.,s);
        vec2 p = floor(uv/sz)*sz + vec2(sz);
        float th = GetTh(p, sz);
        //if (th < 0.1)
        {
            col = vec3(th);//val(p));
            //break;
        }
        //col = vec3(p, 0.0);
        //col = vec3(val(p));
    }
    
    //col = vec3(val(uv));
    fragColor = vec4(col,1.0);
}