#define MAX_STEPS 100
#define MAX_DIST 100.
#define SURF_DIST .001


mat2 Rot(float a) {
    float s = sin(a);
    float c = cos(a);
    return mat2(c, -s, s, c);
}


float sdCylinder(vec3 p, vec3 a, vec3 b, float r) {
    vec3 ab = b-a;
    vec3 ap = p-a;

    float t = dot(ab, ap) / dot(ab, ab);

    vec3 c = a + t*ab;

    float x = length(p-c)-r;
    float y = (abs(t-.5)-.5)*length(ab);
    float e = length(max(vec2(x, y), 0.));
    float i = min(max(x, y), 0.);

    return e+i;
}

float sdTorus(vec3 p, vec2 r) {
    float x = length(p.xz)-r.x;
    return length(vec2(x, p.y))-r.y;
}

vec3 PlaneNormal(vec3 v0, vec3 v1, vec3 v2)
{
    vec3 x = v0 - v1;
    vec3 y = v0 - v2;
    vec3 n = cross(x, y);
    return vec3((n.y < 0.)?-n:n);
}

float dot2( in vec3 v ) { return dot(v,v); }
vec4 udTriangle( vec3 p, vec3 a, vec3 b, vec3 c )
{
    vec3 ba = b - a; vec3 pa = p - a;
    vec3 cb = c - b; vec3 pb = p - b;
    vec3 ac = a - c; vec3 pc = p - c;
    vec3 nor = cross( ba, ac );

    return vec4(sqrt(
        (sign(dot(cross(ba,nor),pa)) +
         sign(dot(cross(cb,nor),pb)) +
         sign(dot(cross(ac,nor),pc))<2.0)
        ?
        min( min(
            dot2(ba*clamp(dot(ba,pa)/dot2(ba),0.0,1.0)-pa),
            dot2(cb*clamp(dot(cb,pb)/dot2(cb),0.0,1.0)-pb) ),
            dot2(ac*clamp(dot(ac,pc)/dot2(ac),0.0,1.0)-pc) )
        :
        dot(nor,pa)*dot(nor,pa)/dot2(nor)), PlaneNormal(a, b, c));
}

vec4 min2( vec4 d1, vec4 d2 )
{
    return (d1.x < d2.x) ? d1 : d2;
}

vec4 Planes(vec3 p)
{
    vec4 p0, p1, p2, p3;
    vec3 a1 = vec3(-3, 1., -1);
    vec3 a2 = vec3(-3., 3., 0.);
    vec3 a3 = vec3(-2., 1., 1.);
    vec3 a4 = vec3(-6., 1., 1.);

    p0 = udTriangle(p, a1, a2, a3);
    p1 = udTriangle(p, a1, a2, a4);
    p2 = udTriangle(p, a2, a3, a4);
    p3 = udTriangle(p, a1, a3, a4);

    return min2(min2(min2(p0, p1), p2), p3);
}

float GetDist(vec3 p)
{
    float planeDist = p.y;

    float td = sdTorus(p-vec3(0,.5,0), vec2(1.5, .4));
    float bd = Planes(p).x;
    float cyld = sdCylinder(p, vec3(0, .7, -3), vec3(3, .7, -1), .3);

    float d = min(td, planeDist);
    d = min(d, bd);

    d = min(d, cyld);

    return d;
}

float RayMarch(vec3 ro, vec3 rd) {
    float dO=0.;

    for(int i=0; i<MAX_STEPS; i++) {
        vec3 p = ro + rd*dO;
        float dS = GetDist(p);
        dO += dS;
        if(dO>MAX_DIST || dS<SURF_DIST) break;
    }

    return dO;
}

vec3 GetNormal(vec3 p) {
    float d = GetDist(p);
    vec2 e = vec2(.001, 0);

    vec3 n = d - vec3(
        GetDist(p-e.xyy),
        GetDist(p-e.yxy),
        GetDist(p-e.yyx));
    if(Planes(p).x <= .01 && Planes(p).x >= 0.)
    {
        return normalize(Planes(p).yzw);
    }
    return normalize(n);
}

float GetLight(vec3 p) {
    vec3 lightPos = vec3(0, 5, 6);
    lightPos.xz += vec2(sin(iTime), cos(iTime))*10.;
    vec3 l = normalize(lightPos-p);
    vec3 n = GetNormal(p);
    float dif = clamp(dot(n, l), 0., 1.);
    float d = RayMarch(p+n*SURF_DIST*2., l);
    if(d<length(lightPos-p)) dif *= .1;

    return dif;
}


vec3 Rot1(vec2 uv, vec3 p, vec3 l, float z) {
    vec3 f = normalize(l-p),
        r = normalize(cross(vec3(0,1,0), f)),
        u = cross(f,r),
        c = p+f*z,
        i = c + uv.x*r + uv.y*u,
        d = normalize(i-p);
    return d;
}

void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    vec2 uv = (fragCoord-.5*iResolution.xy)/iResolution.y;

    vec3 col = vec3(0);

    vec3 ro = vec3(2, 2, -5);
    ro.yz *= Rot(.4);
    ro.xz *= Rot(iTime*.2);
    vec3 rd = Rot1(uv, ro, vec3(0,0,0), .7);
    float d = RayMarch(ro, rd);

    vec3 p = ro + rd * d;

    float dif = GetLight(p);
    col = vec3(dif);

    fragColor = vec4(col,1.0);
}