// vr-MIP.diderot
//
// maximum intensity projection in Diderot
//

input string dataFile;      // name of dataset
input real stepSz;          // size of steps
                            // e.g. 0.5
input vec3 eye;             // location of eye point
                            // e.g. (50,30,20)
input vec3 orig;            // location of pixel (0,0)
                            // e.g. (16.7502,3.81144,16.1159)
input vec3 cVec;            // vector between pixels horizontally
                            // e.g. (-0.0345728,0.0639965,0)
input vec3 rVec;            // vector between pixels vertically
                            // e.g. (0.016857,0.00910666,-0.0701694)

image(3)[] img = load (dataFile);

//field#1(3)[] F = convolve (bspln3, img);
field#2(3)[] F = convolve (bspln3, img);

actor RayCast (int row, int col)
{
    vec3 pos = orig + real(row)*rVec + real(col)*cVec;
    vec3 dir = (pos - eye)/|pos - eye|;
    real t = 0.0;
    real maxval = -inf; 

    update
    {
        vec3 pt = pos + t*dir;
        real val = F@pt;
        maxval = max(val, maxval);
        if (t > 20)
            stabilize;
        t = t + stepSz;
    }

    /* render: output maxval */
}

initially [ RayCast(r, c) | r in 0..199, c in 0..199 ];