// vr-lite-cam
//
// simple volume renderer, now with a single directional light,
// Phong shading, and the new camera.
//

// image parameters
input int imgResU = 480;
input int imgResV = 345;
input real rayStep = 0.1;

// camera controls
input vec3 camEye = [127.331, -1322.05, 272.53];
input vec3 camAt = [63.0, 82.6536, 98.0];
input vec3 camUp = [0.9987, 0.0459166, -0.0221267];
input real camNear = -78.0;
input real camFar = 78.0;
input real camFOV = 5.0;

/* we control the opacity by its center value and the +/- keys */
input real valOpacMid = 550.0;		// 550 for skin, 1300.0 for bone
real valOpacMin = valOpacMid - 150.0;
real valOpacMax = valOpacMid + 150.0;

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);
//vec3 lightRGB = [1.0, 1.0, 1.0];

real phongKa = 0.05;
real phongKd = 0.65;
real phongKs = 0.45;
real phongSp = 50.0;

field#2(3)[] F =  bspln3 ⊛ image("data/vfrhand-nohip.nhdr");

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;
    // ########## BEGIN per-ray initialization
    real rayTransp = 1.0;
//    vec3 rayRGB = [0.0, 0.0, 0.0];
    real rayGrey = 0.0;
    output vec4 outRGBA = [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);
	    if (val > valOpacMin) {  // we have some opacity 
		vec3 grad = ∇F(rayPos);
		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);
          }
          // ##########  END  per-sample code
       }
       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) ];