ray: split scene data from render state

This introduces ray_render_t, and ray_render.[ch].

The _prepared member of ray_scene_t has been moved to ray_render_t,
and the other _prepared members (e.g. objects) will follow.

Up until now I've just been sticking the precomputed state under
_prepared members of their associated structures, and simply using
convention to enforce anything resembling an api boundary.  It's
been convenient without being inefficient, but I'd like to move
the ray code into more of a reusable library and this wart needs
to be addressed.

The render state is also where any spatial indexes will be built
and maintained, another thing I've been experimenting with.

Note most of the churn here is just renaming ray_scene.c to
ray_render.c.  A nearly global s/ray_scene/ray_render/ has occurred,
now that ray_scene_t really only serves as glue to bind objects,
lights, and scene-global properties into a cohesive unit.

1 files changed, 242 insertions, 0 deletions

diff --git a/src/modules/ray/ray_render.c b/src/modules/ray/ray_render.c
new file mode 100644
index 0000000..bfa5112
--- /dev/null
+++ b/src/modules/ray/ray_render.c
@@ -0,0 +1,242 @@
+#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
+
+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_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_object_t	*object;
+
+	for (object = render->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_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_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, &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);
+			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_render_t *render, 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 = render->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_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_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(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_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(ray_scene_t *scene, ray_camera_t *camera)
+{
+	ray_render_t	*render;
+	ray_object_t	*object;
+
+	render = malloc(sizeof(ray_render_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 (object = scene->objects; object->type; object++)
+		ray_object_prepare(object, camera);
+
+	return render;
+}
+
+
+void ray_render_free(ray_render_t *render)
+{
+	free(render);
+}