uniform vec2 position[100];
uniform int NUM;
uniform float blur;
uniform int strength;
uniform vec3 color;
vec2 cubic( in vec2 a, in vec2 b, in vec2 c, in vec2 d, float v1 )
{
    float u1 = 1.0 - v1;
    float u2 = u1*u1;
    float v2 = v1*v1;
    float u3 = u2*u1;
    float v3 = v2*v1;
    return a*u3 + d*v3 + b*3.0*u2*v1 + c*3.0*u1*v2;
}
float length2( in vec2 v ) { return dot(v,v); }
float sdLine2( vec2 p, vec2 a, vec2 b )
{
    vec2 pa = p-a, ba = b-a;

    vec2 bb = pa - ba*clamp( dot(pa,ba)/dot(ba,ba), 0.0, 1.0 );
    float h = clamp( dot(pa,ba)/dot(ba,ba), 0.0, 1.0 );
    return dot(bb,bb);
}

float sdSegment_Expensive( vec2 p, vec2[100] pos,  vec2[100] ta,int num)
{

    float d = 1.;
    float s = 1.0;
    vec2 a,b,na,nb;
    for(int i =0,j=num-1;i<num;j=i,i++){

        a = pos[i];
        b = pos[j];
        na = ta[i];
        nb = ta[j];
    vec2 k1 = (a*2.0+b)/3.0; k1 = a + na*dot(na,k1-a)/dot(na,na);
    vec2 k2 = (b*2.0+a)/3.0; k2 = b + nb*dot(nb,k2-b)/dot(nb,nb);
    float md = length2(p-a);
    vec2 ov = a;
    float ss = 1.0;
    int ll = int(floor(iTime*4.));
    for( int k=1; k<strength; k++ )
    {
        vec2 v = cubic( a, k1, k2, b, float(k+0)/(float(strength)-1.) );
        vec2 e = ov-v;
        vec2 w = p-v;
        // bvec3 c = bvec3(p.y>=b.y,p.y<ov.y,e.x*w.y>e.y*w.x);
       // if( all(c) || all(not(c)) ) ss*=-1.0;
        vec2 b = w - e*clamp( dot(w,e)/dot(e,e), 0.0, 1.0 );


         bvec3 c = bvec3(p.y>=v.y,p.y<ov.y,e.x*w.y>e.y*w.x);
        if( all(c) || all(not(c))) s*=-1.0;
       // float di = sdLine2( p, v, ov );
         ov = v;

        md = min( dot(b,b), md );

    }

         d = min(d,md);




    }
    return sqrt(d)*s;
}

float sdSegment_Cheap( vec2 p, vec2 a, vec2 b, vec2 na, vec2 nb )
{
    // secondary points
    vec2 k1 = (a*2.0+b)/3.0; k1 = a + na*dot(na,k1-a)/dot(na,na);
    vec2 k2 = (b*2.0+a)/3.0; k2 = b + nb*dot(nb,k2-b)/dot(nb,nb);

    vec2 pa = p-a, ba = b-a;
    float h = clamp( dot(pa,ba)/dot(ba,ba), 0.0, 1.0 );

    return sqrt( sdLine2( p, cubic( a, k1, k2, b, clamp( h-0.1, 0.0, 1.0) ),
                             cubic( a, k1, k2, b, clamp( h+0.1, 0.0, 1.0) ) ) );
}

void mainImage( out vec4 fragColor, in vec2 fragCoord )
{

    vec2 uv = fragCoord/iResolution.xy;
    //tangent array
    vec2 tang[100];

    for(int i=0;i<NUM;i++){
        //calculating tangent

        vec2 tangent;
        if(i==0){
             tangent = normalize(position[0]-position[NUM-1])+normalize(position[i+1]-position[i]);
        }
        else
        {
            tangent = normalize(position[i]-position[i-1])+normalize(position[i+1]-position[i]);
        }

        tang[i] = tangent;


    }


    float k = sdSegment_Expensive(uv,position,tang,NUM);

    vec3 col =vec3(clamp(smoothstep(0.2,0.19-blur,k*22.),0.,1.))*color;


    fragColor = vec4(col,1.0);
}