Where Next?
A Final Render
Let’s make the image on the cover of this book -- lots of random spheres.
int main() {
hittable_list world;
auto ground_material = make_shared<lambertian>(color(0.5, 0.5, 0.5));
world.add(make_shared<sphere>(point3(0,-1000,0), 1000, ground_material));
for (int a = -11; a < 11; a++) {
for (int b = -11; b < 11; b++) {
auto choose_mat = random_double();
point3 center(a + 0.9*random_double(), 0.2, b + 0.9*random_double());
if ((center - point3(4, 0.2, 0)).length() > 0.9) {
shared_ptr<material> sphere_material;
if (choose_mat < 0.8) {
// diffuse
auto albedo = color::random() * color::random();
sphere_material = make_shared<lambertian>(albedo);
world.add(make_shared<sphere>(center, 0.2, sphere_material));
} else if (choose_mat < 0.95) {
// metal
auto albedo = color::random(0.5, 1);
auto fuzz = random_double(0, 0.5);
sphere_material = make_shared<metal>(albedo, fuzz);
world.add(make_shared<sphere>(center, 0.2, sphere_material));
} else {
// glass
sphere_material = make_shared<dielectric>(1.5);
world.add(make_shared<sphere>(center, 0.2, sphere_material));
}
}
}
}
auto material1 = make_shared<dielectric>(1.5);
world.add(make_shared<sphere>(point3(0, 1, 0), 1.0, material1));
auto material2 = make_shared<lambertian>(color(0.4, 0.2, 0.1));
world.add(make_shared<sphere>(point3(-4, 1, 0), 1.0, material2));
auto material3 = make_shared<metal>(color(0.7, 0.6, 0.5), 0.0);
world.add(make_shared<sphere>(point3(4, 1, 0), 1.0, material3));
camera cam;
cam.aspect_ratio = 16.0 / 9.0;
cam.image_width = 1200;
cam.samples_per_pixel = 500;
cam.max_depth = 50;
cam.vfov = 20;
cam.lookfrom = point3(13,2,3);
cam.lookat = point3(0,0,0);
cam.vup = vec3(0,1,0);
cam.defocus_angle = 0.6;
cam.focus_dist = 10.0;
cam.render(world);
}
(Note that the code above differs slightly from the project sample code: the samples_per_pixel is
set to 500 above for a high-quality image that will take quite a while to render.
The sample code uses a value of 10 in the interest of reasonable run times while developing and
validating.)
This gives:
An interesting thing you might note is the glass balls don’t really have shadows which makes them look like they are floating. This is not a bug -- you don’t see glass balls much in real life, where they also look a bit strange, and indeed seem to float on cloudy days. A point on the big sphere under a glass ball still has lots of light hitting it because the sky is re-ordered rather than blocked.
Next Steps
You now have a cool ray tracer! What next?
-
Lights -- You can do this explicitly, by sending shadow rays to lights, or it can be done implicitly by making some objects emit light, biasing scattered rays toward them, and then downweighting those rays to cancel out the bias. Both work. I am in the minority in favoring the latter approach.
-
Triangles -- Most cool models are in triangle form. The model I/O is the worst and almost everybody tries to get somebody else’s code to do this.
-
Surface Textures -- This lets you paste images on like wall paper. Pretty easy and a good thing to do.
-
Solid textures -- Ken Perlin has his code online. Andrew Kensler has some very cool info at his blog.
-
Volumes and Media -- Cool stuff and will challenge your software architecture. I favor making volumes have the hittable interface and probabilistically have intersections based on density. Your rendering code doesn’t even have to know it has volumes with that method.
-
Parallelism -- Run $N$ copies of your code on $N$ cores with different random seeds. Average the $N$ runs. This averaging can also be done hierarchically where $N/2$ pairs can be averaged to get $N/4$ images, and pairs of those can be averaged. That method of parallelism should extend well into the thousands of cores with very little coding.
Have fun, and please send me your cool images!