// bmark-diderot.diderot
//
// COPYRIGHT (c) 2011 The Diderot Project (http://diderot-language.cs.uchicago.edu)
// All rights reserved.
//
// simple volume renderer, now with a single directional light,
// Phong shading, and the new camera.
//

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 = 480;
int imgResV = 345;
real rayStep = 0.1;
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*π/360.0)*camDist;
real camUmax = camVmax*real(imgResU)/real(imgResV);

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 = 50.0;

field#2(3)[] F =  bspln3 ⊛ load(dataFile);

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 toEye = normalize(-rayVec);

    real rayN = camVspNear;
    real rayTransp = 1.0;
    real rayGrey = 0.0;
    output vec4 outRGBA = [0.0, 0.0, 0.0, 0.0];

    update {
        vec3 rayPos = camEye + rayN*rayVec;
        if (inside (rayPos,F)) {
           real val = F(rayPos);
           if (val > valOpacMin) {  // we have some opacity 
               vec3 grad = ∇F(rayPos); // (here as easy target for optimization)
               vec3 norm = normalize(-∇F(rayPos));
               real alpha = min(1.0, lerp(0.0, 1.0, valOpacMin, val, valOpacMax));
               real ld = max(0.0, norm • lightDir);
               real hd = max(0.0, norm • normalize(lightDir + toEye));
               real pnt = phongKa 
                          + phongKd * ld 
                          + phongKs * hd^phongSp;
               rayGrey += rayTransp*alpha*pnt;
               rayTransp = rayTransp*(1.0 - alpha);
           }
       }
       if (rayTransp < 0.01) {  // early ray termination
           rayTransp = 0.0;
           stabilize;
       }
       if (rayN > camVspFar) {
           stabilize;
       }
       rayN += rayStep;
    }

    stabilize {
        outRGBA = [rayGrey, rayGrey, rayGrey, 1.0-rayTransp];
    }

}

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