ray: libize raytracer core, introduces src/libs

This is the first step of breaking out all the core rendering stuffs
into reusable libraries and making modules purely compositional,
consumers of various included rendering/effects libraries.

Expect multiple modules leveraging libray for a variety of scenes and
such.  Also expect compositions mixing the various libraries for more
interesting visuals.

1 files changed, 251 insertions, 0 deletions

diff --git a/src/libs/ray/ray_render.c b/src/libs/ray/ray_render.c
new file mode 100644
index 0000000..8b930f6
--- /dev/null
+++ b/src/libs/ray/ray_render.c
@@ -0,0 +1,251 @@
+#include <stdlib.h>
+#include <math.h>
+
+#include "fb.h"
+
+#include "ray_camera.h"
+#include "ray_color.h"
+#include "ray_render_object.h"
+#include "ray_ray.h"
+#include "ray_scene.h"
+
+#define MAX_RECURSION_DEPTH	4
+#define MIN_RELEVANCE		0.05f
+
+typedef struct ray_render_t {
+	const ray_scene_t	*scene;		/* scene being rendered */
+	const ray_camera_t	*camera;	/* camera rendering the scene */
+
+	ray_color_t		ambient_light;
+	ray_camera_frame_t	frame;
+
+	ray_render_object_t	objects[];
+} ray_render_t;
+
+/* Determine if the ray is obstructed by an object within the supplied distance, for shadows */
+static inline int ray_is_obstructed(ray_render_t *render, unsigned depth, ray_ray_t *ray, float distance)
+{
+	ray_render_object_t	*object;
+
+	for (object = render->objects; object->type; object++) {
+		float	ood;
+
+		if (ray_render_object_intersects_ray(object, depth, ray, &ood) &&
+		    ood < distance) {
+			return 1;
+		}
+	}
+
+	return 0;
+}
+
+
+/* shadow test */
+static inline int point_is_shadowed(ray_render_t *render, 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(render, 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_render_t *render, ray_render_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_render_object_surface(object, intersection);
+	ray_color_t	color = ray_3f_mult(&surface.color, &render->ambient_light);
+	ray_object_t	*light;
+
+	/* visit lights for shadows and illumination */
+	for (light = render->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(render, 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);
+			float		intensity = light->light.brightness * (1.0 / (ldist * ldist));
+			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);
+			}
+
+			color = ray_3f_mult_scalar(&color, intensity);
+#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_render_object_t * find_nearest_intersection(ray_render_t *render, ray_render_object_t *reflector, ray_ray_t *ray, unsigned depth, float *res_distance)
+{
+	ray_render_object_t	*nearest_object = NULL;
+	float			nearest_object_distance = INFINITY;
+	ray_render_object_t	*object;
+
+	for (object = render->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_render_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_render_t *render, ray_ray_t *primary_ray)
+{
+	ray_color_t		color = { .x = 0.0f, .y = 0.0f, .z = 0.0f };
+	ray_3f_t		intersection, normal;
+	ray_render_object_t	*reflector = NULL;
+	float			relevance = 1.0f, reflectivity;
+	unsigned		depth = 0;
+	ray_ray_t		reflected_ray, *ray = primary_ray;
+
+	do {
+		ray_render_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(render, 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_render_object_normal(nearest_object, &intersection);
+
+			more_color = shade_intersection(render, 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_render_trace_fragment(ray_render_t *render, fb_fragment_t *fb_fragment)
+{
+	uint32_t		*buf = fb_fragment->buf;
+	ray_camera_fragment_t	fragment;
+	ray_ray_t		ray;
+
+	ray_camera_fragment_begin(&render->frame, fb_fragment, &ray, &fragment);
+	do {
+		do {
+			*buf = ray_color_to_uint32_rgb(trace_ray(render, &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 */
+ray_render_t * ray_render_new(const ray_scene_t *scene, const ray_camera_t *camera)
+{
+	ray_render_t	*render;
+	ray_object_t	*object;
+	unsigned	i;
+
+	for (i = 0, object = scene->objects; object->type; object++)
+		i++;
+
+	render = malloc(sizeof(ray_render_t) + i * sizeof(ray_render_object_t));
+	if (!render)
+		return NULL;
+
+	render->scene = scene;
+	render->camera = camera;
+
+	render->ambient_light = ray_3f_mult_scalar(&scene->ambient_color, scene->ambient_brightness);
+	ray_camera_frame_prepare(camera, &render->frame);
+
+	for (i = 0, object = scene->objects; object->type; object++)
+		render->objects[i++] = ray_render_object_prepare(object, camera);
+
+	return render;
+}
+
+
+void ray_render_free(ray_render_t *render)
+{
+	free(render);
+}