multithreaded-raytracer/include/camera.h

#ifndef CAMERA_H
#define CAMERA_H

#include "hittable.h"
#include "material.h"
#include <thread>
#include <vector>


class camera {
  public:
    
    double aspect_ratio = 1.0;  
    int    image_width  = 100;  
    int samples_per_pixel = 10;
    int max_depth = 10;

    double vfov = 90;
    point3 lookfrom = point3(0,0,0);
    point3 lookat = point3(0,0,-1);
    vec3 vup = vec3(0,1,0);

    
    double defocus_angle = 0;  
    double focus_dist = 10;    

void render(const hittable& world) {
    initialize();

    std::vector<color> framebuffer(image_width * image_height);

    int thread_count = std::thread::hardware_concurrency();
    if (thread_count == 0) thread_count = 8; // fallback

    std::vector<std::thread> threads;
    int rows_per_thread = image_height / thread_count;

    auto render_rows = [&](int start_row, int end_row) {

        for (int j = start_row; j < end_row; j++) {

            for (int i = 0; i < image_width; i++) {

                color pixel_color(0,0,0);

                for (int sample = 0; sample < samples_per_pixel; sample++) {
                    ray r = get_ray(i, j);
                    pixel_color += ray_color(r, max_depth, world);
                }

                framebuffer[j * image_width + i] =
                    pixel_samples_scale * pixel_color;
            }
        }
    };

    for (int t = 0; t < thread_count; t++) {
        int start = t * rows_per_thread;
        int end = (t == thread_count - 1)
                    ? image_height
                    : start + rows_per_thread;

        threads.emplace_back(render_rows, start, end);
    }

    for (auto& t : threads)
        t.join();

    // Print image after rendering completes (single-threaded)
    std::cout << "P3\n" << image_width << ' ' << image_height << "\n255\n";

    for (int j = 0; j < image_height; j++) {
        for (int i = 0; i < image_width; i++) {
            write_color(std::cout,
                framebuffer[j * image_width + i]);
        }
    }

    std::clog << "Done.\n";
}




  private:
    /* Private Camera Variables Here */
    int    image_height;   // Rendered image height
    point3 center;         // Camera center
    double pixel_samples_scale;// color scale factor for a sum of pixel samples
    point3 pixel00_loc;    // Location of pixel 0, 0
    vec3   pixel_delta_u;  // Offset to pixel to the right
    vec3   pixel_delta_v; // Offset to pixel below
    vec3 u,v,w;
    vec3   defocus_disk_u;       // Defocus disk horizontal radius
    vec3   defocus_disk_v;       // Defocus disk vertical radius

    void initialize() {
        image_height = int(image_width / aspect_ratio);
        image_height = (image_height < 1) ? 1 : image_height;

        pixel_samples_scale = 1.0/ samples_per_pixel;

        center = lookfrom;

        

        // Determine viewport dimensions.
        
        auto theta = degrees_to_radians(vfov);
        auto h = std::tan(theta/2);
        auto viewport_height = 2 * h * focus_dist;
        auto viewport_width = viewport_height * (double(image_width)/image_height);

        w = unit_vector(lookfrom - lookat);
        u = unit_vector(cross(vup,w));
        v = cross(w,u);

        // Calculate the vectors across the horizontal and down the vertical viewport edges.
        vec3 viewport_u = viewport_width*u;
        vec3 viewport_v = viewport_height*-v;

        // Calculate the horizontal and vertical delta vectors from pixel to pixel.
        pixel_delta_u = viewport_u / image_width;
        pixel_delta_v = viewport_v / image_height;

        // Calculate the location of the upper left pixel.
        auto viewport_upper_left = center - (focus_dist * w) - viewport_u/2 - viewport_v/2;
        pixel00_loc = viewport_upper_left + 0.5 * (pixel_delta_u + pixel_delta_v);
        
               // Calculate the camera defocus disk basis vectors.
        auto defocus_radius = focus_dist * std::tan(degrees_to_radians(defocus_angle / 2));
        defocus_disk_u = u * defocus_radius;
        defocus_disk_v = v * defocus_radius;

    }

    ray get_ray(int i, int j) const {
        // Construct a camera ray originating from the origin and directed at randomly sampled
        // point around the pixel location i, j.

        auto offset = sample_square();
        auto pixel_sample = pixel00_loc
                          + ((i + offset.x()) * pixel_delta_u)
                          + ((j + offset.y()) * pixel_delta_v);

        auto ray_origin = (defocus_angle <= 0) ? center : defocus_disk_sample();
        auto ray_direction = pixel_sample - ray_origin;

        return ray(ray_origin, ray_direction);
    }

    vec3 sample_square() const {
        // Returns the vector to a random point in the [-.5,-.5]-[+.5,+.5] unit square.
        return vec3(random_double() - 0.5, random_double() - 0.5, 0);
    }

     point3 defocus_disk_sample() const {
        // Returns a random point in the camera defocus disk.
        auto p = random_in_unit_disk();
        return center + (p[0] * defocus_disk_u) + (p[1] * defocus_disk_v);
    }



    color ray_color(const ray& r,int depth, const hittable& world) const {
        if(depth<=0)
            return color(0,0,0);
        
        hit_record rec;

        if (world.hit(r, interval(0.001, infinity), rec)) {
              ray scattered;
            color attenuation;
            if (rec.mat->scatter(r, rec, attenuation, scattered))
                return attenuation * ray_color(scattered, depth-1, world);
            return color(0,0,0);
        }

        vec3 unit_direction = unit_vector(r.direction());
        auto a = 0.5*(unit_direction.y() + 1.0);
        return (1.0-a)*color(1.0, 1.0, 1.0) + a*color(0.5, 0.7, 1.0);
    }

};

#endif