ray: cleanup ray_camera_frame_t fragments

Previously every fb_fragment_t (and thus thread) was constructing
its own ray_camera_frame_t view into the scene, duplicating some
work.

Instead introduce ray_camera_fragment_t to encapsulate the truly
per-fragment state and make ray_scene_render_fragment() operate
on just this stuff with a reference to a shared
ray_camera_frame_t prepared once per-frame.

Some minor ray_camera.c cleanups sneak in as well (prefer multiply
instead of divide, whitespace cleanups...)

5 files changed, 79 insertions, 85 deletions

diff --git a/src/modules/ray/ray.c b/src/modules/ray/ray.c
index ac00806..60784db 100644
--- a/src/modules/ray/ray.c
+++ b/src/modules/ray/ray.c
@@ -154,7 +154,7 @@ static void ray_prepare_frame(void *context, unsigned n_cpus, fb_fragment_t *fra
 /* ray trace a simple scene into the fragment */
 static void ray_render_fragment(void *context, fb_fragment_t *fragment)
 {
-	ray_scene_render_fragment(&scene, &camera, fragment);
+	ray_scene_render_fragment(&scene, fragment);
 }
 
 
diff --git a/src/modules/ray/ray_camera.c b/src/modules/ray/ray_camera.c
index e7792f2..a709d6f 100644
--- a/src/modules/ray/ray_camera.c
+++ b/src/modules/ray/ray_camera.c
@@ -24,62 +24,47 @@ static ray_3f_t project_corner(ray_3f_t *forward, ray_3f_t *left, ray_3f_t *up,
 static void project_corners(ray_camera_t *camera, ray_camera_frame_t *frame)
 {
 	ray_3f_t	forward, left, up, right, down;
-	float		half_horiz = (float)camera->width / 2.0f;
-	float		half_vert = (float)camera->height / 2.0f;
+	float		half_horiz = (float)camera->width * 0.5f;
+	float		half_vert = (float)camera->height * 0.5f;
 
 	ray_euler_basis(&camera->orientation, &forward, &up, &left);
 	right = ray_3f_negate(&left);
 	down = ray_3f_negate(&up);
 
-	frame->nw = project_corner(&forward, &left, &up, camera->focal_length, half_horiz,  half_vert);
-	frame->ne = project_corner(&forward, &right, &up, camera->focal_length, half_horiz,  half_vert);
-	frame->se = project_corner(&forward, &right, &down, camera->focal_length, half_horiz,  half_vert);
-	frame->sw = project_corner(&forward, &left, &down, camera->focal_length, half_horiz,  half_vert);
+	frame->nw = project_corner(&forward, &left, &up, camera->focal_length, half_horiz, half_vert);
+	frame->ne = project_corner(&forward, &right, &up, camera->focal_length, half_horiz, half_vert);
+	frame->se = project_corner(&forward, &right, &down, camera->focal_length, half_horiz, half_vert);
+	frame->sw = project_corner(&forward, &left, &down, camera->focal_length, half_horiz, half_vert);
 }
 
 
-/* Begin a frame for the fragment of camera projection, initializing frame and ray. */
-void ray_camera_frame_begin(ray_camera_t *camera, fb_fragment_t *fragment, ray_ray_t *ray, ray_camera_frame_t *frame)
+/* Prepare a frame of camera projection, initializing res_frame. */
+void ray_camera_frame_prepare(ray_camera_t *camera, ray_camera_frame_t *res_frame)
 {
-	/* References are kept to the camera, fragment, and ray to be traced.
-	 * The ray is maintained as we step through the frame, that is the
-	 * purpose of this api.
-	 *
-	 * Since the ray direction should be a normalized vector, the obvious
-	 * implementation is a bit costly.  The camera frame api hides this
-	 * detail so we can explore interpolation techniques to potentially
-	 * lessen the per-pixel cost.
-	 */
-	frame->camera = camera;
-	frame->fragment = fragment;
-	frame->ray = ray;
-
-	frame->x = frame->y = 0;
-
-	/* From camera->orientation and camera->focal_length compute the vectors
-	 * through the viewport's corners, and place these normalized vectors
-	 * in frame->(nw,ne,sw,se).
-	 *
-	 * These can than be interpolated between to produce the ray vectors
-	 * throughout the frame's fragment.  The efficient option of linear
-	 * interpolation will not maintain the unit vector length, so to
-	 * produce normalized interpolated directions will require the costly
-	 * normalize function.
-	 *
-	 * I'm hoping a simple length correction table can be used to fixup the
-	 * linearly interpolated vectors to make them unit vectors with just
-	 * scalar multiplication instead of the sqrt of normalize.
-	 */
-	project_corners(camera, frame);
-
-	frame->x_delta = 1.0f / (float)camera->width;
-	frame->y_delta = 1.0f / (float)camera->height;
-	frame->x_alpha = frame->x_delta * (float)fragment->x;
-	frame->y_alpha = frame->y_delta * (float)fragment->y;
-
-	frame->cur_w = ray_3f_lerp(&frame->nw, &frame->sw, frame->y_alpha);
-	frame->cur_e = ray_3f_lerp(&frame->ne, &frame->se, frame->y_alpha);
-
-	ray->origin = camera->position;
-	ray->direction = ray_3f_nlerp(&frame->cur_w, &frame->cur_e, frame->x_alpha);
+	res_frame->camera = camera;
+
+	project_corners(camera, res_frame);
+
+	res_frame->x_delta = 1.0f / (float)camera->width;
+	res_frame->y_delta = 1.0f / (float)camera->height;
+}
+
+
+/* Begin a frame's fragment, initializing frame and ray. */
+void ray_camera_fragment_begin(ray_camera_frame_t *frame, fb_fragment_t *fb_fragment, ray_ray_t *res_ray, ray_camera_fragment_t *res_fragment)
+{
+	res_fragment->frame = frame;
+	res_fragment->fb_fragment = fb_fragment;
+	res_fragment->ray = res_ray;
+
+	res_fragment->x = res_fragment->y = 0;
+
+	res_fragment->x_alpha = frame->x_delta * (float)fb_fragment->x;
+	res_fragment->y_alpha = frame->y_delta * (float)fb_fragment->y;
+
+	res_fragment->cur_w = ray_3f_lerp(&frame->nw, &frame->sw, res_fragment->y_alpha);
+	res_fragment->cur_e = ray_3f_lerp(&frame->ne, &frame->se, res_fragment->y_alpha);
+
+	res_ray->origin = frame->camera->position;
+	res_ray->direction = ray_3f_nlerp(&res_fragment->cur_w, &res_fragment->cur_e, res_fragment->x_alpha);
 }
diff --git a/src/modules/ray/ray_camera.h b/src/modules/ray/ray_camera.h
index 191d614..889beb9 100644
--- a/src/modules/ray/ray_camera.h
+++ b/src/modules/ray/ray_camera.h
@@ -21,55 +21,62 @@ typedef struct ray_camera_t {
 
 typedef struct ray_camera_frame_t {
 	ray_camera_t	*camera;		/* the camera supplied to frame_begin() */
-	fb_fragment_t	*fragment;		/* the fragment supplied to frame_begin() */
-	ray_ray_t	*ray;			/* the ray supplied to frame_begin(), which gets updated as we step through the frame. */
 
 	ray_3f_t	nw, ne, sw, se;		/* directions pointing through the corners of the frame fragment */
-	ray_3f_t	cur_w, cur_e;		/* current row's west and east ends */
-	float		x_alpha, y_alpha;	/* interpolation position along the x and y axis */
 	float		x_delta, y_delta;	/* interpolation step delta along the x and y axis */
-	unsigned	x, y;			/* integral position within frame fragment */
 } ray_camera_frame_t;
 
 
-void ray_camera_frame_begin(ray_camera_t *camera, fb_fragment_t *fragment, ray_ray_t *ray, ray_camera_frame_t *frame);
+typedef struct ray_camera_fragment_t {
+	ray_camera_frame_t	*frame;			/* the frame supplied to fragment_begin() */
+	fb_fragment_t		*fb_fragment;		/* the fragment supplied to fragment_begin() */
+	ray_ray_t		*ray;			/* the ray supplied to frame_begin(), which gets updated as we step through the frame. */
 
+	ray_3f_t		cur_w, cur_e;		/* current row's west and east ends */
+	float			x_alpha, y_alpha;	/* interpolation position along the x and y axis */
+	unsigned		x, y;			/* integral position within frame fragment */
+} ray_camera_fragment_t;
 
-/* Step the ray through the frame on the x axis, returns 1 when rays remain on this axis, 0 at the end. */
-/* When 1 is returned, frame->ray is left pointing through the new coordinate. */
-static inline int ray_camera_frame_x_step(ray_camera_frame_t *frame)
+
+void ray_camera_frame_prepare(ray_camera_t *camera, ray_camera_frame_t *res_frame);
+void ray_camera_fragment_begin(ray_camera_frame_t *frame, fb_fragment_t *fb_fragment, ray_ray_t *res_ray, ray_camera_fragment_t *res_fragment);
+
+
+/* Step the ray through the fragment on the x axis, returns 1 when rays remain on this axis, 0 at the end. */
+/* When 1 is returned, fragment->ray is left pointing through the new coordinate. */
+static inline int ray_camera_fragment_x_step(ray_camera_fragment_t *fragment)
 {
-	frame->x++;
+	fragment->x++;
 
-	if (frame->x >= frame->fragment->width) {
-		frame->x = 0;
-		frame->x_alpha = frame->x_delta * (float)frame->fragment->x;
+	if (fragment->x >= fragment->fb_fragment->width) {
+		fragment->x = 0;
+		fragment->x_alpha = fragment->frame->x_delta * (float)fragment->fb_fragment->x;
 		return 0;
 	}
 
-	frame->x_alpha += frame->x_delta;
-	frame->ray->direction = ray_3f_nlerp(&frame->cur_w, &frame->cur_e, frame->x_alpha);
+	fragment->x_alpha += fragment->frame->x_delta;
+	fragment->ray->direction = ray_3f_nlerp(&fragment->cur_w, &fragment->cur_e, fragment->x_alpha);
 
 	return 1;
 }
 
 
-/* Step the ray through the frame on the y axis, returns 1 when rays remain on this axis, 0 at the end. */
-/* When 1 is returned, frame->ray is left pointing through the new coordinate. */
-static inline int ray_camera_frame_y_step(ray_camera_frame_t *frame)
+/* Step the ray through the fragment on the y axis, returns 1 when rays remain on this axis, 0 at the end. */
+/* When 1 is returned, fragment->ray is left pointing through the new coordinate. */
+static inline int ray_camera_fragment_y_step(ray_camera_fragment_t *fragment)
 {
-	frame->y++;
+	fragment->y++;
 
-	if (frame->y >= frame->fragment->height) {
-		frame->y = 0;
-		frame->y_alpha = frame->y_delta * (float)frame->fragment->y;
+	if (fragment->y >= fragment->fb_fragment->height) {
+		fragment->y = 0;
+		fragment->y_alpha = fragment->frame->y_delta * (float)fragment->fb_fragment->y;
 		return 0;
 	}
 
-	frame->y_alpha += frame->y_delta;
-	frame->cur_w = ray_3f_lerp(&frame->nw, &frame->sw, frame->y_alpha);
-	frame->cur_e = ray_3f_lerp(&frame->ne, &frame->se, frame->y_alpha);
-	frame->ray->direction = ray_3f_nlerp(&frame->cur_w, &frame->cur_e, frame->x_alpha);
+	fragment->y_alpha += fragment->frame->y_delta;
+	fragment->cur_w = ray_3f_lerp(&fragment->frame->nw, &fragment->frame->sw, fragment->y_alpha);
+	fragment->cur_e = ray_3f_lerp(&fragment->frame->ne, &fragment->frame->se, fragment->y_alpha);
+	fragment->ray->direction = ray_3f_nlerp(&fragment->cur_w, &fragment->cur_e, fragment->x_alpha);
 
 	return 1;
 }
diff --git a/src/modules/ray/ray_scene.c b/src/modules/ray/ray_scene.c
index 2026f6d..cf8fb44 100644
--- a/src/modules/ray/ray_scene.c
+++ b/src/modules/ray/ray_scene.c
@@ -189,22 +189,22 @@ static inline ray_color_t trace_ray(ray_scene_t *scene, ray_ray_t *primary_ray)
 }
 
 
-void ray_scene_render_fragment(ray_scene_t *scene, ray_camera_t *camera, fb_fragment_t *fragment)
+void ray_scene_render_fragment(ray_scene_t *scene, fb_fragment_t *fb_fragment)
 {
-	ray_camera_frame_t	frame;
+	unsigned		stride = fb_fragment->stride / 4;
+	uint32_t		*buf = fb_fragment->buf;
+	ray_camera_fragment_t	fragment;
 	ray_ray_t		ray;
-	uint32_t		*buf = fragment->buf;
-	unsigned		stride = fragment->stride / 4;
 
-	ray_camera_frame_begin(camera, fragment, &ray, &frame);
+	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_frame_x_step(&frame));
+		} while (ray_camera_fragment_x_step(&fragment));
 
 		buf += stride;
-	} while (ray_camera_frame_y_step(&frame));
+	} while (ray_camera_fragment_y_step(&fragment));
 }
 
 
@@ -216,6 +216,7 @@ 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);
+	ray_camera_frame_prepare(camera, &scene->_prepared.frame);
 
 	for (i = 0; i < scene->n_objects; i++)
 		ray_object_prepare(&scene->objects[i], camera);
diff --git a/src/modules/ray/ray_scene.h b/src/modules/ray/ray_scene.h
index 98928ee..1fe736c 100644
--- a/src/modules/ray/ray_scene.h
+++ b/src/modules/ray/ray_scene.h
@@ -20,11 +20,12 @@ typedef struct ray_scene_t {
 	float			ambient_brightness;
 
 	struct {
-		ray_color_t	ambient_light;
+		ray_color_t		ambient_light;
+		ray_camera_frame_t	frame;
 	} _prepared;
 } ray_scene_t;
 
 void ray_scene_prepare(ray_scene_t *scene, ray_camera_t *camera);
-void ray_scene_render_fragment(ray_scene_t *scene, ray_camera_t *camera, fb_fragment_t *fragment);
+void ray_scene_render_fragment(ray_scene_t *scene, fb_fragment_t *fb_fragment);
 
 #endif