// vr-lite-cam
//
// simple volume renderer, now with a single directional light,
// Phong shading, and the new camera.
//
// The main thing missing from this is a more general
// transfer function

//string dataFile = "../data/txs-pad3.nrrd";
//vec3 camEye = [25.0, 15.0, 10.0];
//vec3 camAt = [3.0, 3.0, 3.0];
//vec3 camUp = [0.0, 0.0, 1.0];
//real camNear = -5.0;
//real camFar = 5.0;
//real camFOV = 18.0;
//int imgResU = 480;
//int imgResV = 345;
//real rayStep = 0.1;
//real valOpacMin = 0.20;          // highest value with opacity 0.0
//real valOpacMax = 0.25;          // lowest value with opacity 1.0 

string dataFile = "../data/vfrhand-nohip.nhdr";
vec3 camEye = [127.331, -1322.05, 272.53];
vec3 camAt = [63.0, 82.6536, 98.0];
vec3 camUp = [0.9987, 0.0459166, -0.0221267];
real camNear = -78.0;
real camFar = 78.0;
real camFOV = 5.0;
//int imgResU = 640;
//int imgResV = 480;
int imgResU = 480;
int imgResV = 345;
//int imgResU = 320;
//int imgResV = 240;
// HEY (BUG?) do we intend to allow inconsistent redefinitions of things?
real rayStep = 0.1;
real rayStep = 0.5;
real valOpacMin = 400.0;        // 400.0 for skin, 1150.0 for bone
real valOpacMax = 700.0;        // 700.0 for skin, 1450.0 for bone

real camDist = |camAt - camEye|;
real camVspNear = camDist + camNear;
real camVspFar = camDist + camFar;
vec3 camN = normalize(camAt - camEye);
vec3 camU = normalize(camN × camUp);
vec3 camV = camN × camU;
real camVmax = tan(camFOV*3.1415926536/360.0)*camDist;
real camUmax = camVmax*real(imgResU)/real(imgResV);

// HEY (BUG): these:
//   vec3 lightVspDir = [1.0, -0.0, 0.0];
//   vec3 lightVspDir = [1.0, 0.0, -0.0];
// work okay but this:
//   vec3 lightVspDir = [1.0, 0.0, 0.0];
// does not:
// uncaught exception Fail [Fail: E_Slice]
//   raised at simplify/eval.sml:266.57
//   raised at simplify/eval.sml:183.33-183.47
vec3 lightVspDir = [0.9, -1.0, -2.5];
vec3 lightDir = normalize(lightVspDir[0]*camU + lightVspDir[1]*camV + lightVspDir[2]*camN);

real phongKa = 0.05;
real phongKd = 0.80;
real phongKs = 0.20;
real phongSp = 30.0;

image(3)[] img = load (dataFile);
//field#4(3)[] F = img ⊛ bspln5;
field#2(3)[] F = img ⊛ bspln3;
//field#1(3)[] F = img ⊛ ctmr;
//field#0(3)[] F = img ⊛ tent;

strand RayCast (int ui, int vi)
{
    real rayU = lerp(-camUmax, camUmax, -0.5, real(ui), real(imgResU)-0.5);
    real rayV = lerp(-camVmax, camVmax, -0.5, real(vi), real(imgResV)-0.5);
    vec3 rayVec = (camDist*camN + rayU*camU + rayV*camV)/camDist;
    vec3 rayDir = normalize(rayVec);

    real rayN = camVspNear;
    // ########## BEGIN per-ray initialization
    real transp = 1.0;
    real gray = 0.0;
    output vec4 rgba = [0.0, 0.0, 0.0, 0.0];
    // ##########  END  per-ray initialization

    update
    {
       vec3 rayPos = camEye + rayN*rayVec;
       if (inside (rayPos,F)) {
          // ########## BEGIN per-sample code
          real val = F@rayPos;
          vec3 grad = ∇F@rayPos; // (here as easy target for optimization)
	  vec3 norm = normalize(-∇F@rayPos);
          if (val > valOpacMin) {  // we have some opacity 
              real opac = min(1.0, lerp(0.0, 1.0, valOpacMin, val, valOpacMax));
              real ld = norm • lightDir;
              real hd = norm • normalize(lightDir + normalize(camEye - rayPos));
              real mat = (  phongKa
                          + phongKd*(ld if ld > 0.0 else 0.0)
                          + phongKs*(pow(hd, phongSp) if hd > 0.0 else 0.0));
              gray = gray + transp*opac*mat;
              transp = transp*(1.0 - opac);
          }
          // ##########  END  per-sample code
       }
       if (transp < 0.01) {  // early ray termination
           transp = 0.0;
           rgba = [gray, gray, gray, 1.0-transp]; /* FIXME */
           stabilize;
       }
       if (t > 40.0) {
           rgba = [gray, gray, gray, 1.0-transp]; /* FIXME */
           stabilize;
       }
       t = t + stepSz;
    }

    stabilize {
//     rgba = [gray, gray, gray, 1.0-transp];
    }

}

initially [ RayCast(ui, vi) | vi in 0..(imgResV-1), ui in 0..(imgResU-1) ];