Converted GLSL

precision highp float;
uniform vec3 iResolution;
uniform vec2 iMouse;
uniform float iTime;

float dot2( in vec2 v ) { return dot(v,v); }
float dot2( in vec3 v ) { return dot(v,v); }
float ndot( in vec2 a, in vec2 b ) { return a.x*b.x - a.y*b.y; }
float sdPlane( vec3 p )
{
    return p.y;
}

float sdSphere( vec3 p, float s )
{
    return length(p)-s;
}

float sdBox( vec3 p, vec3 b )
{
    vec3 d = abs(p) - b;
    return min(max(d.x,max(d.y,d.z)),0.0) + length(max(d,0.0));
}

float sdBoundingBox( vec3 p, vec3 b, float e )
{
    p = abs(p)-b;
    vec3 q = abs(p+e)-e;

    return min(min(
        length(max(vec3(p.x,q.y,q.z),0.0))+min(max(p.x,max(q.y,q.z)),0.0),
        length(max(vec3(q.x,p.y,q.z),0.0))+min(max(q.x,max(p.y,q.z)),0.0)),
        length(max(vec3(q.x,q.y,p.z),0.0))+min(max(q.x,max(q.y,p.z)),0.0));
}
float sdEllipsoid( in vec3 p, in vec3 r ) // approximated
{
    float k0 = length(p/r);
    float k1 = length(p/(r*r));
    return k0*(k0-1.0)/k1;
}

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

float sdCappedTorus(in vec3 p, in vec2 sc, in float ra, in float rb)
{
    p.x = abs(p.x);
    float k = (sc.y*p.x>sc.x*p.y) ? dot(p.xy,sc) : length(p.xy);
    return sqrt( dot(p,p) + ra*ra - 2.0*ra*k ) - rb;
}

float sdHexPrism( vec3 p, vec2 h )
{
    vec3 q = abs(p);

    const vec3 k = vec3(-0.8660254, 0.5, 0.57735);
    p = abs(p);
    p.xy -= 2.0*min(dot(k.xy, p.xy), 0.0)*k.xy;
    vec2 d = vec2(
        length(p.xy - vec2(clamp(p.x, -k.z*h.x, k.z*h.x), h.x))*sign(p.y - h.x),
        p.z-h.y );
    return min(max(d.x,d.y),0.0) + length(max(d,0.0));
}

float sdOctogonPrism( in vec3 p, in float r, float h )
{
  const vec3 k = vec3(-0.9238795325,   // sqrt(2+sqrt(2))/2
                       0.3826834323,   // sqrt(2-sqrt(2))/2
                       0.4142135623 ); // sqrt(2)-1
    // reflections
    p = abs(p);
    p.xy -= 2.0*min(dot(vec2( k.x,k.y),p.xy),0.0)*vec2( k.x,k.y);
    p.xy -= 2.0*min(dot(vec2(-k.x,k.y),p.xy),0.0)*vec2(-k.x,k.y);
    // polygon side
    p.xy -= vec2(clamp(p.x, -k.z*r, k.z*r), r);
    vec2 d = vec2( length(p.xy)*sign(p.y), p.z-h );
    return min(max(d.x,d.y),0.0) + length(max(d,0.0));
}

float sdCapsule( vec3 p, vec3 a, vec3 b, float r )
{
    vec3 pa = p-a, ba = b-a;
    float h = clamp( dot(pa,ba)/dot(ba,ba), 0.0, 1.0 );
    return length( pa - ba*h ) - r;
}

float sdRoundCone( in vec3 p, in float r1, float r2, float h )
{
    vec2 q = vec2( length(p.xz), p.y );

    float b = (r1-r2)/h;
    float a = sqrt(1.0-b*b);
    float k = dot(q,vec2(-b,a));

    if( k < 0.0 ) return length(q) - r1;
    if( k > a*h ) return length(q-vec2(0.0,h)) - r2;

    return dot(q, vec2(a,b) ) - r1;
}

float sdRoundCone(vec3 p, vec3 a, vec3 b, float r1, float r2)
{
    // sampling independent computations (only depend on shape)
    vec3  ba = b - a;
    float l2 = dot(ba,ba);
    float rr = r1 - r2;
    float a2 = l2 - rr*rr;
    float il2 = 1.0/l2;

    // sampling dependant computations
    vec3 pa = p - a;
    float y = dot(pa,ba);
    float z = y - l2;
    float x2 = dot2( pa*l2 - ba*y );
    float y2 = y*y*l2;
    float z2 = z*z*l2;

    // single square root!
    float k = sign(rr)*rr*rr*x2;
    if( sign(z)*a2*z2 > k ) return  sqrt(x2 + z2)        *il2 - r2;
    if( sign(y)*a2*y2 < k ) return  sqrt(x2 + y2)        *il2 - r1;
                            return (sqrt(x2*a2*il2)+y*rr)*il2 - r1;
}

float sdTriPrism( vec3 p, vec2 h )
{
    float k = sqrt(3.0);
    h.x *= 0.5*k;
    p.xy /= h.x;
    p.x = abs(p.x) - 1.0;
    p.y = p.y + 1.0/k;
    if( p.x+k*p.y>0.0 ) p.xy=vec2(p.x-k*p.y,-k*p.x-p.y)/2.0;
    p.x -= clamp( p.x, -2.0, 0.0 );
    float d1 = length(p.xy)*sign(-p.y)*h.x;
    float d2 = abs(p.z)-h.y;
    return length(max(vec2(d1,d2),0.0)) + min(max(d1,d2), 0.);
}

// vertical
float sdCylinder( vec3 p, vec2 h )
{
    vec2 d = abs(vec2(length(p.xz),p.y)) - h;
    return min(max(d.x,d.y),0.0) + length(max(d,0.0));
}

// arbitrary orientation
float sdCylinder(vec3 p, vec3 a, vec3 b, float r)
{
    vec3 pa = p - a;
    vec3 ba = b - a;
    float baba = dot(ba,ba);
    float paba = dot(pa,ba);

    float x = length(pa*baba-ba*paba) - r*baba;
    float y = abs(paba-baba*0.5)-baba*0.5;
    float x2 = x*x;
    float y2 = y*y*baba;
    float d = (max(x,y)<0.0)?-min(x2,y2):(((x>0.0)?x2:0.0)+((y>0.0)?y2:0.0));
    return sign(d)*sqrt(abs(d))/baba;
}

// vertical
float sdCone( in vec3 p, in vec2 c, float h )
{
    vec2 q = h*vec2(c.x,-c.y)/c.y;
    vec2 w = vec2( length(p.xz), p.y );

    vec2 a = w - q*clamp( dot(w,q)/dot(q,q), 0.0, 1.0 );
    vec2 b = w - q*vec2( clamp( w.x/q.x, 0.0, 1.0 ), 1.0 );
    float k = sign( q.y );
    float d = min(dot( a, a ),dot(b, b));
    float s = max( k*(w.x*q.y-w.y*q.x),k*(w.y-q.y)  );
    return sqrt(d)*sign(s);
}

float sdCappedCone( in vec3 p, in float h, in float r1, in float r2 )
{
    vec2 q = vec2( length(p.xz), p.y );

    vec2 k1 = vec2(r2,h);
    vec2 k2 = vec2(r2-r1,2.0*h);
    vec2 ca = vec2(q.x-min(q.x,(q.y < 0.0)?r1:r2), abs(q.y)-h);
    vec2 cb = q - k1 + k2*clamp( dot(k1-q,k2)/dot2(k2), 0.0, 1.0 );
    float s = (cb.x < 0.0 && ca.y < 0.0) ? -1.0 : 1.0;
    return s*sqrt( min(dot2(ca),dot2(cb)) );
}

float sdCappedCone(vec3 p, vec3 a, vec3 b, float ra, float rb)
{
    float rba  = rb-ra;
    float baba = dot(b-a,b-a);
    float papa = dot(p-a,p-a);
    float paba = dot(p-a,b-a)/baba;

    float x = sqrt( papa - paba*paba*baba );

    float cax = max(0.0,x-((paba<0.5)?ra:rb));
    float cay = abs(paba-0.5)-0.5;

    float k = rba*rba + baba;
    float f = clamp( (rba*(x-ra)+paba*baba)/k, 0.0, 1.0 );

    float cbx = x-ra - f*rba;
    float cby = paba - f;

    float s = (cbx < 0.0 && cay < 0.0) ? -1.0 : 1.0;

    return s*sqrt( min(cax*cax + cay*cay*baba,
        cbx*cbx + cby*cby*baba) );
}

// c is the sin/cos of the desired cone angle
float sdSolidAngle(vec3 pos, vec2 c, float ra)
{
    vec2 p = vec2( length(pos.xz), pos.y );
    float l = length(p) - ra;
    float m = length(p - c*clamp(dot(p,c),0.0,ra) );
    return max(l,m*sign(c.y*p.x-c.x*p.y));
}

float sdOctahedron(vec3 p, float s)
{
    p = abs(p);
    float m = p.x + p.y + p.z - s;

    // exact distance
    vec3 o = min(3.0*p - m, 0.0);
    o = max(6.0*p - m*2.0 - o*3.0 + (o.x+o.y+o.z), 0.0);
    return length(p - s*o/(o.x+o.y+o.z));

    // exact distance
    // #if 1
    // vec3 q;
    // if( 3.0*p.x < m ) q = p.xyz;
    // else if( 3.0*p.y < m ) q = p.yzx;
    // else if( 3.0*p.z < m ) q = p.zxy;
    // else return m*0.57735027;
    // float k = clamp(0.5*(q.z-q.y+s),0.0,s);
    // return length(vec3(q.x,q.y-s+k,q.z-k));
    // #endif

    // bound, not exact
    return m*0.57735027;
}

float sdPyramid( in vec3 p, in float h )
{
    float m2 = h*h + 0.25;

    // symmetry
    p.xz = abs(p.xz);
    p.xz = (p.z>p.x) ? p.zx : p.xz;
    p.xz -= 0.5;

    // project into face plane (2D)
    vec3 q = vec3( p.z, h*p.y - 0.5*p.x, h*p.x + 0.5*p.y);

    float s = max(-q.x,0.0);
    float t = clamp( (q.y-0.5*p.z)/(m2+0.25), 0.0, 1.0 );

    float a = m2*(q.x+s)*(q.x+s) + q.y*q.y;
    float b = m2*(q.x+0.5*t)*(q.x+0.5*t) + (q.y-m2*t)*(q.y-m2*t);

    float d2 = min(q.y,-q.x*m2-q.y*0.5) > 0.0 ? 0.0 : min(a,b);

    // recover 3D and scale, and add sign
    return sqrt( (d2+q.z*q.z)/m2 ) * sign(max(q.z,-p.y));;
}

// la,lb=semi axis, h=height, ra=corner
float sdRhombus(vec3 p, float la, float lb, float h, float ra)
{
    p = abs(p);
    vec2 b = vec2(la,lb);
    float f = clamp( (ndot(b,b-2.0*p.xz))/dot(b,b), -1.0, 1.0 );
    vec2 q = vec2(length(p.xz-0.5*b*vec2(1.0-f,1.0+f))*sign(p.x*b.y+p.z*b.x-b.x*b.y)-ra, p.y-h);
    return min(max(q.x,q.y),0.0) + length(max(q,0.0));
}

//------------------------------------------------------------------

vec2 opU( vec2 d1, vec2 d2 )
{
    return (d1.x<d2.x) ? d1 : d2;
}

//------------------------------------------------------------------

vec2 map( in vec3 pos )
{
    vec2 res = vec2( 1e10, 0.0 );
        res = opU( res, vec2( sdSphere(    pos-vec3(-2.0,0.25, 0.0), 0.25 ), 26.9 ) );

    // bounding box
    if( sdBox( pos-vec3(0.0,0.3,-1.0),vec3(0.35,0.3,2.5) )<res.x )
    {
    // more primitives
    res = opU( res, vec2( sdBoundingBox( pos-vec3( 0.0,0.25, 0.0), vec3(0.3,0.25,0.2), 0.025 ), 16.9 ) );
    res = opU( res, vec2( sdTorus(      (pos-vec3( 0.0,0.30, 1.0)).xzy, vec2(0.25,0.05) ), 25.0 ) );
    res = opU( res, vec2( sdCone(        pos-vec3( 0.0,0.45,-1.0), vec2(0.6,0.8),0.45 ), 55.0 ) );
    res = opU( res, vec2( sdCappedCone(  pos-vec3( 0.0,0.25,-2.0), 0.25, 0.25, 0.1 ), 13.67 ) );
    res = opU( res, vec2( sdSolidAngle(  pos-vec3( 0.0,0.00,-3.0), vec2(3,4)/5.0, 0.4 ), 49.13 ) );
    }

    // bounding box
    if( sdBox( pos-vec3(1.0,0.3,-1.0),vec3(0.35,0.3,2.5) )<res.x )
    {
    // more primitives
    res = opU( res, vec2( sdCappedTorus((pos-vec3( 1.0,0.30, 1.0))*vec3(1,-1,1), vec2(0.866025,-0.5), 0.25, 0.05), 8.5) );
    res = opU( res, vec2( sdBox(         pos-vec3( 1.0,0.25, 0.0), vec3(0.3,0.25,0.1) ), 3.0 ) );
    res = opU( res, vec2( sdCapsule(     pos-vec3( 1.0,0.00,-1.0),vec3(-0.1,0.1,-0.1), vec3(0.2,0.4,0.2), 0.1  ), 31.9 ) );
    res = opU( res, vec2( sdCylinder(    pos-vec3( 1.0,0.25,-2.0), vec2(0.15,0.25) ), 8.0 ) );
    res = opU( res, vec2( sdHexPrism(    pos-vec3( 1.0,0.2,-3.0), vec2(0.2,0.05) ), 18.4 ) );
    }

    // bounding box
    if( sdBox( pos-vec3(-1.0,0.35,-1.0),vec3(0.35,0.35,2.5))<res.x )
    {
    // more primitives
    res = opU( res, vec2( sdPyramid(    pos-vec3(-1.0,-0.6,-3.0), 1.0 ), 13.56 ) );
    res = opU( res, vec2( sdOctahedron( pos-vec3(-1.0,0.15,-2.0), 0.35 ), 23.56 ) );
    res = opU( res, vec2( sdTriPrism(   pos-vec3(-1.0,0.15,-1.0), vec2(0.3,0.05) ),43.5 ) );
    res = opU( res, vec2( sdEllipsoid(  pos-vec3(-1.0,0.25, 0.0), vec3(0.2, 0.25, 0.05) ), 43.17 ) );
    res = opU( res, vec2( sdRhombus(   (pos-vec3(-1.0,0.34, 1.0)).xzy, 0.15, 0.25, 0.04, 0.08 ),17.0 ) );
    }

    // bounding box
    if( sdBox( pos-vec3(2.0,0.3,-1.0),vec3(0.35,0.3,2.5) )<res.x )
    {
    // more primitives
    res = opU( res, vec2( sdOctogonPrism(pos-vec3( 2.0,0.2,-3.0), 0.2, 0.05), 51.8 ) );
    res = opU( res, vec2( sdCylinder(    pos-vec3( 2.0,0.15,-2.0), vec3(0.1,-0.1,0.0), vec3(-0.2,0.35,0.1), 0.08), 31.2 ) );
    res = opU( res, vec2( sdCappedCone(  pos-vec3( 2.0,0.10,-1.0), vec3(0.1,0.0,0.0), vec3(-0.2,0.40,0.1), 0.15, 0.05), 46.1 ) );
    res = opU( res, vec2( sdRoundCone(   pos-vec3( 2.0,0.15, 0.0), vec3(0.1,0.0,0.0), vec3(-0.1,0.35,0.1), 0.15, 0.05), 51.7 ) );
    res = opU( res, vec2( sdRoundCone(   pos-vec3( 2.0,0.20, 1.0), 0.2, 0.1, 0.3 ), 37.0 ) );
    }

    return res;
}

// http://iquilezles.org/www/articles/boxfunctions/boxfunctions.htm
vec2 iBox( in vec3 ro, in vec3 rd, in vec3 rad )
{
    vec3 m = 1.0/rd;
    vec3 n = m*ro;
    vec3 k = abs(m)*rad;
    vec3 t1 = -n - k;
    vec3 t2 = -n + k;
    return vec2( max( max( t1.x, t1.y ), t1.z ),
                min( min( t2.x, t2.y ), t2.z ) );
}

vec2 raycast( in vec3 ro, in vec3 rd )
{
    vec2 res = vec2(-1.0,-1.0);

    float tmin = 1.0;
    float tmax = 20.0;

    // raytrace floor plane
    float tp1 = (0.0-ro.y)/rd.y;
    if( tp1>0.0 )
    {
        tmax = min( tmax, tp1 );
        res = vec2( tp1, 1.0 );
    }
    //else return res;

    // raymarch primitives
    vec2 tb = iBox( ro-vec3(0.0,0.4,-0.5), rd, vec3(2.5,0.41,3.0) );
    if( tb.x<tb.y && tb.y>0.0 && tb.x<tmax)
    {
        //return vec2(tb.x,2.0);
        tmin = max(tb.x,tmin);
        tmax = min(tb.y,tmax);

        float t = tmin;
        for(int i=0; (i < 70) && (t < tmax); i++)
        {
            vec2 h = map( ro+rd*t );
            if( abs(h.x)<(0.0001*t) )
            {
                res = vec2(t,h.y);
                break;
            }
            t += h.x;
        }
    }

    return res;
}

// http://iquilezles.org/www/articles/rmshadows/rmshadows.htm
float calcSoftshadow( in vec3 ro, in vec3 rd, in float mint, in float tmax )
{
    // bounding volume
    float tp = (0.8-ro.y)/rd.y; if( tp>0.0 ) tmax = min( tmax, tp );

    float res = 1.0;
    float t = mint;
    for( int i=0; i<24; i++ )
    {
        float h = map( ro + rd*t ).x;
        float s = clamp(8.0*h/t,0.0,1.0);
        res = min( res, s*s*(3.0-2.0*s) );
        t += clamp( h, 0.02, 0.2 );
        if( res<0.004 || t>tmax ) break;
    }
    return clamp( res, 0.0, 1.0 );
}

// http://iquilezles.org/www/articles/normalsSDF/normalsSDF.htm
vec3 calcNormal( in vec3 pos )
{
    vec2 e = vec2(1.0,-1.0)*0.5773*0.0005;
    return normalize( e.xyy*map( pos + e.xyy ).x +
                        e.yyx*map( pos + e.yyx ).x +
                        e.yxy*map( pos + e.yxy ).x +
                        e.xxx*map( pos + e.xxx ).x );
}

float calcAO( in vec3 pos, in vec3 nor )
{
    float occ = 0.0;
    float sca = 1.0;
    for( int i=0; i<5; i++ )
    {
        float h = 0.01 + 0.12*float(i)/4.0;
        float d = map( pos + h*nor ).x;
        occ += (h-d)*sca;
        sca *= 0.95;
        if( occ>0.35 ) break;
    }
    return clamp( 1.0 - 3.0*occ, 0.0, 1.0 ) * (0.5+0.5*nor.y);
}

// http://iquilezles.org/www/articles/checkerfiltering/checkerfiltering.htm
float checkersGradBox( in vec2 p, in vec2 dpdx, in vec2 dpdy )
{
    // filter kernel
    vec2 w = abs(dpdx)+abs(dpdy) + 0.001;
    // analytical integral (box filter)
    vec2 i = 2.0*(abs(fract((p-0.5*w)*0.5)-0.5)-abs(fract((p+0.5*w)*0.5)-0.5))/w;
    // xor pattern
    return 0.5 - 0.5*i.x*i.y;
}

vec3 render( in vec3 ro, in vec3 rd, in vec3 rdx, in vec3 rdy )
{
    // background
    vec3 col = vec3(0.7, 0.7, 0.9) - max(rd.y,0.0)*0.3;

    // raycast scene
    vec2 res = raycast(ro,rd);
    float t = res.x;
    float m = res.y;
    if( m>-0.5 )
    {
        vec3 pos = ro + t*rd;
        vec3 nor = (m<1.5) ? vec3(0.0,1.0,0.0) : calcNormal( pos );
        vec3 ref = reflect( rd, nor );

        // material
        col = 0.2 + 0.2*sin( m*2.0 + vec3(0.0,1.0,2.0) );
        float ks = 1.0;

        if( m<1.5 )
        {
            // project pixel footprint into the plane
            vec3 dpdx = ro.y*(rd/rd.y-rdx/rdx.y);
            vec3 dpdy = ro.y*(rd/rd.y-rdy/rdy.y);

            float f = checkersGradBox( 3.0*pos.xz, 3.0*dpdx.xz, 3.0*dpdy.xz );
            col = 0.15 + f*vec3(0.05);
            ks = 0.4;
        }

        // lighting
        float occ = calcAO( pos, nor );

        vec3 lin = vec3(0.0);

        // sun
        {
            vec3  lig = normalize( vec3(-0.5, 0.4, -0.6) );
            vec3  hal = normalize( lig-rd );
            float dif = clamp( dot( nor, lig ), 0.0, 1.0 );
            //if( dif>0.0001 )
                  dif *= calcSoftshadow( pos, lig, 0.02, 2.5 );
            float spe = pow( clamp( dot( nor, hal ), 0.0, 1.0 ),16.0);
                  spe *= dif;
                  spe *= 0.04+0.96*pow(clamp(1.0-dot(hal,lig),0.0,1.0),5.0);
                //spe *= 0.04+0.96*pow(clamp(1.0-sqrt(0.5*(1.0-dot(rd,lig))),0.0,1.0),5.0);
            lin += col*2.20*dif*vec3(1.30,1.00,0.70);
            lin +=     5.00*spe*vec3(1.30,1.00,0.70)*ks;
        }
        // sky
        {
            float dif = sqrt(clamp( 0.5+0.5*nor.y, 0.0, 1.0 ));
                  dif *= occ;
            float spe = smoothstep( -0.2, 0.2, ref.y );
                  spe *= dif;
                  spe *= 0.04+0.96*pow(clamp(1.0+dot(nor,rd),0.0,1.0), 5.0 );
            //if( spe>0.001 )
                  spe *= calcSoftshadow( pos, ref, 0.02, 2.5 );
            lin += col*0.60*dif*vec3(0.40,0.60,1.15);
            lin +=     2.00*spe*vec3(0.40,0.60,1.30)*ks;
        }
        // back
        {
            float dif = clamp( dot( nor, normalize(vec3(0.5,0.0,0.6))), 0.0, 1.0 )*clamp( 1.0-pos.y,0.0,1.0);
                    dif *= occ;
            lin += col*0.55*dif*vec3(0.25,0.25,0.25);
        }
        // sss
        {
            float dif = pow(clamp(1.0+dot(nor,rd),0.0,1.0),2.0);
                  dif *= occ;
            lin += col*0.25*dif*vec3(1.00,1.00,1.00);
        }

        col = lin;

        col = mix( col, vec3(0.7,0.7,0.9), 1.0-exp( -0.0001*t*t*t ) );
    }

    return vec3( clamp(col,0.0,1.0) );
}

mat3 setCamera( in vec3 ro, in vec3 ta, float cr )
{
    vec3 cw = normalize(ta-ro);
    vec3 cp = vec3(sin(cr), cos(cr),0.0);
    vec3 cu = normalize( cross(cw,cp) );
    vec3 cv =          ( cross(cu,cw) );
    return mat3( cu, cv, cw );
}

void main(void) {
    vec2 fragCoord = gl_FragCoord.xy;

    vec2 mo = iMouse.xy/iResolution.xy;
    float time = 32.0 + iTime*1.5;

    // camera
    vec3 ta = vec3( 0.5, -0.5, -0.6 );
    vec3 ro = ta + vec3( 4.5*cos(0.1*time + 7.0*mo.x), 1.3 + 2.0*mo.y, 4.5*sin(0.1*time + 7.0*mo.x) );
    // camera-to-world transformation
    mat3 ca = setCamera( ro, ta, 0.0 );

    vec3 tot = vec3(0.0);
    for( int m=0; m<2; m++ ) {
        for( int n=0; n<2; n++ )
        {
            // pixel coordinates
            vec2 o = vec2(float(m),float(n)) / float(2) - 0.5;
            vec2 p = (2.0*(fragCoord+o)-iResolution.xy)/iResolution.y;

            // focal length
            const float fl = 2.5;

            // ray direction
            vec3 rd = ca * normalize( vec3(p,fl) );

            // ray differentials
            vec2 px = (2.0*(fragCoord+vec2(1.0,0.0))-iResolution.xy)/iResolution.y;
            vec2 py = (2.0*(fragCoord+vec2(0.0,1.0))-iResolution.xy)/iResolution.y;
            vec3 rdx = ca * normalize( vec3(px,fl) );
            vec3 rdy = ca * normalize( vec3(py,fl) );

            // render
            vec3 col = render( ro, rd, rdx, rdy );

            // gain
            // col = col*3.0/(2.5+col);

            // gamma
            col = pow( col, vec3(0.4545) );

            tot += col;
        }
    }
    tot /= float(2*2);

    gl_FragColor = vec4( tot, 1.0 );
}