// 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 = 320;
//int imgResV = 240;
//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

 // HEY: update this camera code when possible, based on eventual
// improvements to mip-cam.diderot
real camDist = |camAt - camEye|;
real camVspNear = camDist + camNear;
real camVspFar = camDist + camFar;
vec3 camN = (camAt - camEye)/camDist;
vec3 tmp0 = cross(camN,camUp); 
vec3 camU = tmp0/|tmp0|;
vec3 camV = cross(camN,camU);
real camVmax = tan(camFOV*3.1415926536/360.0)*camDist;
real camUmax = camVmax*real(imgResU)/real(imgResV);

vec3 lightVspDir = [0.9, -1.0, -2.5];
// HEY (want) ability to access components of a vector (e.g. "vec[0]")
// would make this transform to world-space less awkward; would be
// lightVspDir[0]*camU + lightVspDir[1]*camV + lightVspDir[2]*camN
// OR, we could create and apply a view-to-world matrix transform
vec3 tmp2 = (  dot(lightVspDir,[1.0,0.0,0.0])*camU 
             + dot(lightVspDir,[0.0,1.0,0.0])*camV
             + dot(lightVspDir,[0.0,0.0,1.0])*camN);
vec3 lightDir = tmp2/|tmp2|;

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

image(3)[] img = load (dataFile);
//field#2(3)[] F = img ⊛ bspln3;
field#2(3)[] F = img ⊛ bspln3;
// HEY (BUG): ctmr Catmull-Rom is C1 but not C2 continuous
//field#2(3)[] F = img ⊛ ctmr;
//field#0(3)[] F = img ⊛ tent;

strand RayCast (int ui, int vi)
{
    real rayU = 2.0*camUmax*(real(ui) + 0.5)/real(imgResU) - camUmax;
    real rayV = 2.0*camVmax*(real(vi) + 0.5)/real(imgResV) - camVmax;
    vec3 rayVec = (camDist*camN + rayU*camU + rayV*camV)/camDist;
    vec3 rayDir = rayVec/|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;
          vec3 norm = -grad/|grad|;
          // HEY (BUG) will get an "uncaught exception" if code is instead
          // vec3 norm = -∇F@rayPos/|∇F@rayPos|;
          if (val > valOpacMin) {  // we have some opacity 
              real opac =
                 1.0 if (val > valOpacMax)
                 else (val - valOpacMin)/(valOpacMax - valOpacMin);
              real ld = dot(lightDir,norm);
              real mat = (  phongKa
                          + phongKd*(ld if ld > 0.0 else 0.0)
                          + phongKs*(pow(ld, phongSp) if ld > 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
          rgba = [gray, gray, gray, 1.0];
          stabilize;
       }
       if (rayN > camVspFar) {
          rgba = [gray, gray, gray, 1.0-transp];
          stabilize;
       }
       rayN = rayN + rayStep;
    }

    /* render: output maxval */
}

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