A non recursive implementation of ray_color #624
Description
I would like to suggest a simple non recursive implementation for ray_color function to be mentioned in an alternative listing during the first book around chapter 8.
I realize that it is maybe outside of the current scope of the first book, where everything is as simple as possible. However, since portability is also a concern for the first book, and it is not possible to use recursion in glsl and OpenCL, it might help to briefly at least mention a non recursive implementation from which the reader might build her own version for more complicated stuff later on.
Here is my proposition:
color ray_color2(const Ray &r, const HittableList &scene, int depth) {
Ray r_in = Ray(r.origin, r.direction);
color rcolor = color(1,1,1);
while (true) {
HitRecord record;
if (depth <= 0) {
// final case
return color(0);
}
if (scene.hit(r_in, 0.001, INF, record)) {
// recursive case
point3 target = record.point + random_in_hemisphere(record.normal);
r_in = Ray(record.point, target - record.point);
depth--;
rcolor *= 0.5;
} else {
// no hit so bye
vec3 direction = unit_vector(r_in.direction);
double temp = 0.5 * (direction.y() + 1.0);
rcolor *= (1.0 - temp) * color(1,1,1) + temp * color(0.5, 0.7, 1.0);
return rcolor;
}
}
}Note that I am not using any call stack to emulate the recursion. The function correctly renders the figure in Rendering of diffuse spheres with hemispherical scattering, I also ported it to glsl and it works over there as well.