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#include <stdio.h>
#include <math.h>
#include "vector.h"
#include "ray.h"
// https://en.wikipedia.org/wiki/Line%E2%80%93sphere_intersection
// http://viclw17.github.io/2018/07/16/raytracing-ray-sphere-intersection/
// https://www.scratchapixel.com/lessons/3d-basic-rendering/minimal-ray-tracer-rendering-simple-shapes/ray-sphere-intersection
COORD_T ray_intersect_sphere(sphere_t *s, ray_t *ray, bool skip_dist)
{
// Vector between vector start and center of circle
vector_t oc;
vector_sub(&oc, ray->start, s->center);
// Solve quadratic function
// TODO Not sure if this step i neccesary because dir is unit
COORD_T a = vector_dot(ray->direction, ray->direction);
COORD_T b = 2 * vector_dot(&oc, ray->direction);
COORD_T c = vector_dot(&oc, &oc) - s->radius * s->radius;
COORD_T d = b * b - 4 * a * c;
// no intersection
if (d < 0) {
return -1;
}
if (skip_dist) {
return 1;
}
// Else take the closest intersection, reuse d
COORD_T q = (b > 0) ?
-0.5 * (b + sqrt(d)) :
-0.5 * (b - sqrt(d));
COORD_T x0 = q / a;
COORD_T x1 = c / q;
// Take the correct result. If one is zero take the other.
if (x0 <= 0) {
if (x1 <= 0) {
return -1;
}
x0 = x1;
}
// If point is on sphere it will be zero close to zero
if (x0 < 1e-3) {
return -1;
}
return x0;
}
// Requires that vectors are normalized
// https://www.scratchapixel.com/lessons/3d-basic-rendering/minimal-ray-tracer-rendering-simple-shapes/ray-plane-and-ray-disk-intersection
COORD_T ray_intersect_plane(plane_t *p, ray_t *ray, bool skip_dist)
{
// If zero ray is parralel to plane
COORD_T nr = vector_dot(p->norm, ray->direction);
//
// Take care of rounding errors
if (nr < ZERO_APROX && nr > -ZERO_APROX) {
return -1;
}
if (skip_dist) {
return 1;
}
// Calculate distance
vector_t tmp;
vector_copy(&tmp, p->start);
vector_sub(&tmp, &tmp, ray->start);
COORD_T t = vector_dot(&tmp, p->norm) / nr;
return t;
}
COORD_T ray_intersect(object_t *o, ray_t *ray, bool skip_dist)
{
switch (o->type) {
case TYPE_PLANE:
return ray_intersect_plane(&o->pl, ray, skip_dist);
case TYPE_SPHERE:
return ray_intersect_sphere(&o->sph, ray, skip_dist);
default:
printf("Unknown object type %d\n", o->type);
return -1;
}
}
// If chk is true, will return at first hit less than chk_dist
object_t *ray_cast(space_t *s, ray_t *r, COORD_T *dist_ret, bool chk, COORD_T chk_dist)
{
object_t *o = s->objects;
object_t *smallest = NULL;
COORD_T dist = 0;
while (o) {
COORD_T d = ray_intersect(o, r, false);
if (d > 0) {
if (chk && chk_dist > d) {
if (dist_ret) {
*dist_ret = d;
}
return o;
}
if (d < dist || smallest == NULL) {
dist = d;
smallest = o;
}
}
o = o->next;
}
if (chk) {
return NULL;
}
if (dist_ret) {
*dist_ret = dist;
}
return smallest;
}
color_t *ray_trace(space_t *s, unsigned int x, unsigned int y)
{
// Setup primary ray
ray_t r;
r.start = &s->view.position;
r.direction = vector_copy(NULL, NULL);
viewpoint_ray(&s->view, r.direction, x, y);
// Cast it
COORD_T dist;
object_t *o = ray_cast(s, &r, &dist, false, 0);
if (!o) {
return NULL;
}
//printf("dist: %f\n", dist);
// Calculate new ray point
r.start = vector_scale(NULL, r.direction, dist);
vector_add(r.start, r.start, &s->view.position);
// Cast light rays
light_t *l = s->lights;
while (l) {
vector_t tmp;
// Calculate distance to light
vector_sub(&tmp, l->pos, r.start);
COORD_T d = vector_len(&tmp);
// Calculate unit
vector_scale_inv(&tmp, &tmp, vector_len(&tmp));
// Find obstacles
r.direction = &tmp;
object_t *obs = ray_cast(s, &r, NULL, true, d);
if (!obs) {
return color_set(NULL, 100, 100, o->type == TYPE_SPHERE ? 200 :0);
}
l = l->next;
}
return NULL;
}
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