#include "viewing_ray.h"

void viewing_ray(
    const Camera & camera,
    const int i,
    const int j,
    const int width,
    const int height,
    Ray & ray)
{
    /**
     * Based on
     * Fundamentals in Computer Graphics - Fourth Edition, Chapter 4.3.2 Perspective views.
     * Steve Marschner & Peter Shirley
     */

    /* Determine the direction of the ray, using the camera and pixel location. */
    double u = 0 - camera.width / 2 + camera.width * (j + 0.5) / width;
    double v = 0 - camera.height / 2 + camera.height * (i + 0.5) / height;

    ray.origin = camera.e;
    ray.direction = (0 - camera.d) * camera.w + u * camera.u + v * camera.v;
}