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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
static ray_color_t trace_ray(ray_scene_t *scene, ray_ray_t *ray, unsigned depth);
/* 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)
{
unsigned i;
for (i = 0; i < scene->n_objects; i++) {
float ood;
if (ray_object_intersects_ray(&scene->objects[i], 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;
/* negate the light vector so it's pointed at the light rather than from it */
shadow_ray.direction = ray_3f_negate(light_direction);
/* we must shift the origin slightly (epsilon) towards the light to
* prevent spurious self-obstruction at the ray:object intersection */
shadow_ray.origin = ray_3f_mult_scalar(&shadow_ray.direction, 0.00001f);
shadow_ray.origin = ray_3f_add(&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_ray(ray_scene_t *scene, ray_ray_t *ray, ray_object_t *object, float distance, unsigned depth)
{
ray_surface_t surface;
ray_color_t color;
ray_3f_t rvec = ray_3f_mult_scalar(&ray->direction, distance);
ray_3f_t intersection = ray_3f_sub(&ray->origin, &rvec);
ray_3f_t normal = ray_object_normal(object, &intersection);
unsigned i;
surface = ray_object_surface(object, &intersection);
color = ray_3f_mult(&surface.color, &scene->_prepared.ambient_light);
/* visit lights for shadows and illumination */
for (i = 0; i < scene->n_lights; i++) {
ray_3f_t lvec = ray_3f_sub(&scene->lights[i].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;
ray_color_t specular;
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) {
/* FIXME: assumes light is a point for its color */
specular = ray_3f_mult_scalar(&scene->lights[i].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
}
}
/* generate a reflection ray */
#if 1
if (depth < MAX_RECURSION_DEPTH) {
float dot = ray_3f_dot(&ray->direction, &normal);
ray_ray_t reflected_ray = { .direction = ray_3f_mult_scalar(&normal, dot * 2.0f) };
ray_3f_t reflection;
reflected_ray.origin = intersection;
reflected_ray.direction = ray_3f_sub(&ray->direction, &reflected_ray.direction);
reflection = trace_ray(scene, &reflected_ray, depth);
reflection = ray_3f_mult_scalar(&reflection, surface.specular);
color = ray_3f_add(&color, &reflection);
}
#endif
/* TODO: generate a refraction ray */
return color;
}
static ray_color_t trace_ray(ray_scene_t *scene, ray_ray_t *ray, unsigned depth)
{
ray_object_t *nearest_object = NULL;
float nearest_object_distance = INFINITY;
ray_color_t color = { .x = 0.0, .y = 0.0, .z = 0.0 };
unsigned i;
depth++;
for (i = 0; i < scene->n_objects; i++) {
float distance;
/* Does this ray intersect object? */
if (ray_object_intersects_ray(&scene->objects[i], depth, ray, &distance)) {
/* Is it the nearest intersection? */
if (distance < nearest_object_distance) {
nearest_object = &scene->objects[i];
nearest_object_distance = distance;
}
}
}
if (nearest_object)
color = shade_ray(scene, ray, nearest_object, nearest_object_distance, depth);
depth--;
return color;
}
void ray_scene_render_fragment(ray_scene_t *scene, ray_camera_t *camera, fb_fragment_t *fragment)
{
ray_camera_frame_t frame;
ray_ray_t ray;
uint32_t *buf = fragment->buf;
unsigned stride = fragment->stride / 4;
ray_camera_frame_begin(camera, fragment, &ray, &frame);
do {
do {
*buf = ray_color_to_uint32_rgb(trace_ray(scene, &ray, 0));
buf++;
} while (ray_camera_frame_x_step(&frame));
buf += stride;
} while (ray_camera_frame_y_step(&frame));
}
/* 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)
{
unsigned i;
scene->_prepared.ambient_light = ray_3f_mult_scalar(&scene->ambient_color, scene->ambient_brightness);
for (i = 0; i < scene->n_objects; i++)
ray_object_prepare(&scene->objects[i], camera);
}
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