main.cpp

#include "rtweekend.h"

#include "color.h"
#include "hittable_list.h"
#include "sphere.h"
#include "camera.h"
#include "material.h"


#include <iostream>
#include <fstream>


/**
 * @brief 
 * checks if a ray hits a sphere by outlining it's dimensions
 * such as R^2 = X^2 + y^2 + Z^2 and using algebra, it 
 * becomes t^2b⋅b+2tb⋅(A−C)+(A−C)⋅(A−C)−r^2=0
 */
double hit_sphere(const point3& center, double radius, const ray& r) {
    vec3 oc = r.origin() - center;
    auto a = r.direction().length_squared();
    auto half_b = dot(oc, r.direction());
    auto c = oc.length_squared() - radius*radius;
    auto discriminant = half_b*half_b - a*c;
    if (discriminant < 0) {return -1.0;}
    else{return (-half_b - sqrt(discriminant)) / a;}
}

color ray_color(const ray& r, const hittable& world, int depth) {
    hit_record rec;

    //If we've exceeded the ray bounce limit, no more light is gathered.
    if (depth <=0) {
        return color(0,0,0);
    }
    if (world.hit(r, 0.001, infinity, rec)) {
        ray scattered;
        color attenuation;
        if (rec.mat_ptr->scatter(r, rec, attenuation, scattered))
            return attenuation * ray_color(scattered, world, depth-1);
        return color(0,0,0);
    }
    vec3 unit_direction = unit_vector(r.direction());
    auto t = 0.5*(unit_direction.y() + 1.0);
    return (1.0-t)*color(1.0, 1.0, 1.0) + t*color(0.5, 0.7, 1.0);
}

int main() {
    // File
    std::fstream myfile;

    // Image
    const auto aspect_ratio = 16.0 / 9.0;
    const int image_width = 1200;
    const int image_height = static_cast<int>(image_width / aspect_ratio);
    const int samples_per_pixel = 100;
    const int max_depth = 50;

    // World
    hittable_list world;
    

    auto material_ground = make_shared<lambertian>(color(0.8, 0.8, 0.0));
    auto material_center = make_shared<lambertian>(color(0.7, 0.3, 0.3));
    auto material_left   = make_shared<metal>(color(0.8, 0.8, 0.8), 0.3);
    auto material_right  = make_shared<metal>(color(0.8, 0.6, 0.2), 1.0);

    world.add(make_shared<sphere>(point3( 0.0, -100.5, -1.0), 100.0, material_ground));
    world.add(make_shared<sphere>(point3( 0.0,    0.0, -1.0),   0.5, material_center));
    world.add(make_shared<sphere>(point3(-1.0,    0.0, -1.0),   0.5, material_left));
    world.add(make_shared<sphere>(point3( 1.0,    0.0, -1.0),   0.5, material_right));


    //Camera
    camera cam;

    // Render
    myfile.open("./image.ppm", std::fstream::out);
    myfile << "P3\n" << image_width << ' ' << image_height << "\n255\n";
    for (int j = image_height-1; j >= 0; --j) {
        std::cerr << "\rScanlines remaining: " << j << ' ' << std::flush;
        for (int i = 0; i < image_width; ++i) {
            color pixel_color(0,0,0);
            for (int s = 0; s < samples_per_pixel; ++s) {
                auto u = (i + random_double()) / (image_width-1);
                auto v = (j + random_double()) / (image_height-1);
                ray r = cam.get_ray(u, v);
                pixel_color += ray_color(r, world, max_depth);
            }
            write_color(myfile, pixel_color, samples_per_pixel);
        }
    }
    myfile.close();
    std::cerr << "Done.\n";
}