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#include <stdlib.h>
#include <math.h>
#include "fb.h"
#include "ray_camera.h"
#include "ray_color.h"
#include "ray_object.h"
#include "ray_ray.h"
#include "ray_scene.h"
#define MAX_RECURSION_DEPTH 4
#define MIN_RELEVANCE 0.05f
/* Determine if the ray is obstructed by an object within the supplied distance, for shadows */
static inline int ray_is_obstructed(ray_scene_t *scene, unsigned depth, ray_ray_t *ray, float distance)
{
ray_object_t *object;
for (object = scene->objects; object->type; object++) {
float ood;
if (ray_object_intersects_ray(object, depth, ray, &ood) &&
ood < distance) {
return 1;
}
}
return 0;
}
/* shadow test */
static inline int point_is_shadowed(ray_scene_t *scene, unsigned depth, ray_3f_t *light_direction, float distance, ray_3f_t *point)
{
ray_ray_t shadow_ray;
shadow_ray.direction = *light_direction;
shadow_ray.origin = *point;
if (ray_is_obstructed(scene, depth + 1, &shadow_ray, distance))
return 1;
return 0;
}
/* a faster powf() that's good enough for our purposes.
* XXX: note there's a faster technique which exploits the IEEE floating point format:
* https://github.com/ekmett/approximate/blob/master/cbits/fast.c#L185
*/
static inline float approx_powf(float x, float y)
{
return expf(y * logf(x));
}
/* Determine the color @ distance on ray on object viewed from origin */
static inline ray_color_t shade_intersection(ray_scene_t *scene, ray_object_t *object, ray_ray_t *ray, ray_3f_t *intersection, ray_3f_t *normal, unsigned depth, float *res_reflectivity)
{
ray_surface_t surface = ray_object_surface(object, intersection);
ray_color_t color = ray_3f_mult(&surface.color, &scene->_prepared.ambient_light);
ray_object_t *light;
/* visit lights for shadows and illumination */
for (light = scene->lights; light->type; light++) {
ray_3f_t lvec = ray_3f_sub(&light->light.emitter.point.center, intersection);
float ldist = ray_3f_length(&lvec);
float lvec_normal_dot;
lvec = ray_3f_mult_scalar(&lvec, (1.0f / ldist)); /* normalize lvec */
#if 1
if (point_is_shadowed(scene, depth, &lvec, ldist, intersection))
continue;
#endif
lvec_normal_dot = ray_3f_dot(normal, &lvec);
if (lvec_normal_dot > 0) {
#if 1
float rvec_lvec_dot = ray_3f_dot(&ray->direction, &lvec);
ray_color_t diffuse;
diffuse = ray_3f_mult_scalar(&surface.color, lvec_normal_dot);
diffuse = ray_3f_mult_scalar(&diffuse, surface.diffuse);
color = ray_3f_add(&color, &diffuse);
if (rvec_lvec_dot > 0) {
ray_color_t specular;
/* FIXME: assumes light is a point for its color */
specular = ray_3f_mult_scalar(&light->light.emitter.point.surface.color, approx_powf(rvec_lvec_dot, surface.highlight_exponent));
specular = ray_3f_mult_scalar(&specular, surface.specular);
color = ray_3f_add(&color, &specular);
}
#else
ray_color_t diffuse;
diffuse = ray_3f_mult_scalar(&surface.color, lvec_normal_dot);
color = ray_3f_add(&color, &diffuse);
#endif
}
}
/* for now just treat specular as the reflectivity */
*res_reflectivity = surface.specular;
return color;
}
static inline ray_object_t * find_nearest_intersection(ray_scene_t *scene, ray_object_t *reflector, ray_ray_t *ray, unsigned depth, float *res_distance)
{
ray_object_t *nearest_object = NULL;
float nearest_object_distance = INFINITY;
ray_object_t *object;
for (object = scene->objects; object->type; object++) {
float distance;
/* Don't bother checking if a reflected ray intersects the object reflecting it,
* reflector = NULL for primary rays, which will never compare as true here. */
if (object == reflector)
continue;
/* Does this ray intersect object? */
if (ray_object_intersects_ray(object, depth, ray, &distance)) {
/* Is it the nearest intersection? */
if (distance < nearest_object_distance) {
nearest_object = object;
nearest_object_distance = distance;
}
}
}
if (nearest_object)
*res_distance = nearest_object_distance;
return nearest_object;
}
static inline ray_color_t trace_ray(ray_scene_t *scene, ray_ray_t *primary_ray)
{
ray_color_t color = { .x = 0.0f, .y = 0.0f, .z = 0.0f };
ray_3f_t intersection, normal;
ray_object_t *reflector = NULL;
float relevance = 1.0f, reflectivity;
unsigned depth = 0;
ray_ray_t reflected_ray, *ray = primary_ray;
do {
ray_object_t *nearest_object;
float nearest_distance;
if (reflector) {
float dot = ray_3f_dot(&ray->direction, &normal);
ray_3f_t new_direction = ray_3f_mult_scalar(&normal, dot * 2.0f);
new_direction = ray_3f_sub(&ray->direction, &new_direction);
reflected_ray.origin = intersection;
reflected_ray.direction = new_direction;
ray = &reflected_ray;
}
nearest_object = find_nearest_intersection(scene, reflector, ray, depth, &nearest_distance);
if (nearest_object) {
ray_3f_t more_color;
ray_3f_t rvec;
rvec = ray_3f_mult_scalar(&ray->direction, nearest_distance);
intersection = ray_3f_add(&ray->origin, &rvec);
normal = ray_object_normal(nearest_object, &intersection);
more_color = shade_intersection(scene, nearest_object, ray, &intersection, &normal, depth, &reflectivity);
more_color = ray_3f_mult_scalar(&more_color, relevance);
color = ray_3f_add(&color, &more_color);
}
reflector = nearest_object;
} while (reflector && (++depth < MAX_RECURSION_DEPTH) && (relevance *= reflectivity) >= MIN_RELEVANCE);
return color;
}
void ray_scene_render_fragment(ray_scene_t *scene, fb_fragment_t *fb_fragment)
{
uint32_t *buf = fb_fragment->buf;
ray_camera_fragment_t fragment;
ray_ray_t ray;
ray_camera_fragment_begin(&scene->_prepared.frame, fb_fragment, &ray, &fragment);
do {
do {
*buf = ray_color_to_uint32_rgb(trace_ray(scene, &ray));
buf++;
} while (ray_camera_fragment_x_step(&fragment));
buf = ((void *)buf) + fb_fragment->stride;
} while (ray_camera_fragment_y_step(&fragment));
}
/* prepare the scene for rendering with camera, must be called whenever anything in the scene+camera pair has been changed. */
/* this is basically a time for the raytracer to precompute whatever it can which otherwise ends up occurring per-ray */
/* the camera is included so primary rays which all have a common origin may be optimized for */
void ray_scene_prepare(ray_scene_t *scene, ray_camera_t *camera)
{
ray_object_t *object;
scene->_prepared.ambient_light = ray_3f_mult_scalar(&scene->ambient_color, scene->ambient_brightness);
ray_camera_frame_prepare(camera, &scene->_prepared.frame);
for (object = scene->objects; object->type; object++)
ray_object_prepare(object, camera);
}
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