#include "camera.h"

#include <math.h>

#ifndef M_PI
#define M_PI 3.14159265258979323846264
#endif

static const vec3_t up = { 0.0, 1.0, 0.0 };

camera_t camera_init(
    vec3_t pos, vec3_t target, double fov, uint32_t img_width,
    uint32_t img_height)
{
	const double fov_rad = M_PI * fov / 180.0;
	const double aspect = (double)img_width / (double)img_height;
	const double viewport_height = tan(fov_rad / 2);
	const double viewport_width = viewport_height * aspect;

	const vec3_t w_hat = vec3_unit(vec3_sub(target, pos));
	const vec3_t u_hat = vec3_unit(vec3_cross(up, w_hat));
	const vec3_t v_hat = vec3_unit(vec3_cross(w_hat, u_hat));

	const vec3_t u = vec3_scale(u_hat, viewport_width);
	const vec3_t v = vec3_scale(v_hat, -viewport_height);

	const vec3_t topleft
	    = vec3_sub(vec3_add(pos, w_hat), vec3_scale(vec3_add(u, v), 0.5));

	const vec3_t x_step = vec3_scale(u, 1.0 / (double)img_width);
	const vec3_t y_step = vec3_scale(v, 1.0 / (double)img_height);
	const vec3_t pix_origin
	    = vec3_add(topleft, vec3_scale(vec3_add(x_step, y_step), 0.5));

	return (camera_t) {
		.pos = pos,
		.pix_origin = pix_origin,
		.x_step = x_step,
		.y_step = y_step,
		.img_width = img_width,
		.img_height = img_height,
	};
}