A simple volume renderer in Diderot

The following code is a simple diffuse-only volume rendering with head-light written in Diderot. It uses an opacity function that varies linearly between two values. This example illustrates the use of probing both a field and its gradient.

input string dataFile; // name of dataset input real stepSz = 0.1; // size of steps input vec3 eye; // location of eye point input vec3 orig; // location of pixel (0,0) input vec3 cVec; // vector between pixels horizontally input vec3 rVec; // vector between pixels vertically input real valOpacMin; // highest value with opacity 0.0 input real valOpacMax; // lowest value with opacity 1.0 image(3)[] img = load (dataFile); field#1(3)[] F = img ⊛ bspln3; 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 transp = 1.0; real gray = 0.0; output vec4 rgba = [0.0, 0.0, 0.0, 0.0]; update { pos = pos + stepSz*dir; if (inside (pos,F)) { real val = F@pos; vec3 grad = ∇F@pos; vec3 norm = -grad / |grad|; if (val > valOpacMin) { // we have some opacity real opac = 1.0 if (val > valOpacMax) else (val - valOpacMin)/(valOpacMax - valOpacMin); gray = gray + transp*opac*max(0.0, dot(-dir,norm)); transp = transp*(1.0 - opac); } } if (transp < 0.01) { // early ray termination transp = 0.0; stabilize; } if (t > 40.0) { stabilize; } t = t + stepSz; } stabilize { rgba = [gray, gray, gray, 1.0-transp]; } } initially [ RayCast(r, c) | r in 0..199, c in 0..199 ];