til: til_fb_fragment_t **fragment_ptr all the things

Preparatory commit for enabling cloneable/swappable fragments

There's an outstanding issue with the til_fb_page_t submission,
see comments.  Doesn't matter for now since cloning doesn't happen
yet, but will need to be addressed before they do.

29 files changed, 182 insertions, 127 deletions

diff --git a/src/main.c b/src/main.c
index 7f6557b..8648b8e 100644
--- a/src/main.c
+++ b/src/main.c
@@ -319,15 +319,28 @@ static void * rototiller_thread(void *_rt)
 	struct timeval	now;
 
 	for (;;) {
-		til_fb_page_t	*page;
-		unsigned	ticks;
+		til_fb_page_t		*page;
+		til_fb_fragment_t	*fragment;
+		unsigned		ticks;
 
 		page = til_fb_page_get(rt->fb);
+		fragment = &page->fragment;
 
 		gettimeofday(&now, NULL);
 		ticks = get_ticks(&rt->start_tv, &now, rt->ticks_offset);
 
-		til_module_render(rt->module_context, ticks, &page->fragment);
+		/* XXX FIXME this needs refactoring, maybe til_fb_fragment_ops_t needs
+		 * to implement the page_put, then til_fb_page_get() just returns a
+		 * fragment with a put method.
+		 *
+		 * I've hacked it for now, but it's broken once cloning becomes a thing
+		 * because we assume that page contains fragment @ put time.  When a
+		 * clone could have replaced the fragment, and it's the replacement page
+		 * that must be submitted.  what makes a page?  being submittable, so
+		 * maybe just make submit another op on the fragment and get rid of the
+		 * til_fb_page_t type altogether... hacked to build for now.
+		 */
+		til_module_render(rt->module_context, ticks, &fragment);
 
 		til_fb_page_put(rt->fb, page);
 	}
diff --git a/src/modules/blinds/blinds.c b/src/modules/blinds/blinds.c
index aa71ddd..d3cddf2 100644
--- a/src/modules/blinds/blinds.c
+++ b/src/modules/blinds/blinds.c
@@ -83,9 +83,10 @@ static inline void draw_blind_vertical(til_fb_fragment_t *fragment, unsigned col
 
 
 /* draw blinds over the fragment */
-static void blinds_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t *fragment)
+static void blinds_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t **fragment_ptr)
 {
 	blinds_context_t	*ctxt = (blinds_context_t *)context;
+	til_fb_fragment_t	*fragment = *fragment_ptr;
 
 	static float rr;
 
diff --git a/src/modules/checkers/checkers.c b/src/modules/checkers/checkers.c
index 20ecd63..32b5aa3 100644
--- a/src/modules/checkers/checkers.c
+++ b/src/modules/checkers/checkers.c
@@ -200,9 +200,10 @@ static int checkers_fragmenter(til_module_context_t *context, const til_fb_fragm
 }
 
 
-static void checkers_prepare_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t *fragment, til_frame_plan_t *res_frame_plan)
+static void checkers_prepare_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t **fragment_ptr, til_frame_plan_t *res_frame_plan)
 {
 	checkers_context_t	*ctxt = (checkers_context_t *)context;
+	til_fb_fragment_t	*fragment = *fragment_ptr;
 
 	/* XXX: note cpu_affinity is required when fill_module is used, to ensure module_contexts
 	 * have a stable relationship to fragnum.  Otherwise the output would be unstable because the
@@ -227,9 +228,11 @@ static inline unsigned hash(unsigned x)
 }
 
 
-static void checkers_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t *fragment)
+static void checkers_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t **fragment_ptr)
 {
 	checkers_context_t	*ctxt = (checkers_context_t *)context;
+	til_fb_fragment_t	*fragment = *fragment_ptr;
+
 	uint32_t		color = ctxt->setup.color, flags = 0;
 	checkers_fill_t		fill = ctxt->setup.fill;
 	int			state;
@@ -293,7 +296,7 @@ static void checkers_render_fragment(til_module_context_t *context, unsigned tic
 			til_fb_fragment_fill(fragment, flags, color);
 		else {
 			/* TODO: we need a way to send down color and flags, and use the module render as a brush of sorts */
-			til_module_render(ctxt->fill_module_contexts[cpu], ticks, fragment);
+			til_module_render(ctxt->fill_module_contexts[cpu], ticks, fragment_ptr);
 		}
 	}
 }
diff --git a/src/modules/compose/compose.c b/src/modules/compose/compose.c
index ff32ac4..922a9b9 100644
--- a/src/modules/compose/compose.c
+++ b/src/modules/compose/compose.c
@@ -49,7 +49,7 @@ typedef struct compose_setup_t {
 
 static til_module_context_t * compose_create_context(unsigned seed, unsigned ticks, unsigned n_cpus, til_setup_t *setup);
 static void compose_destroy_context(til_module_context_t *context);
-static void compose_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t *fragment);
+static void compose_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t **fragment_ptr);
 static int compose_setup(const til_settings_t *settings, til_setting_t **res_setting, const til_setting_desc_t **res_desc, til_setup_t **res_setup);
 
 static compose_setup_t compose_default_setup = {
@@ -125,9 +125,10 @@ static void compose_destroy_context(til_module_context_t *context)
 }
 
 
-static void compose_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t *fragment)
+static void compose_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t **fragment_ptr)
 {
 	compose_context_t	*ctxt = (compose_context_t *)context;
+	til_fb_fragment_t	*fragment = *fragment_ptr, *texture = &ctxt->texture_fb;
 
 	if (ctxt->texture.module) {
 		if (!ctxt->texture_fb.buf ||
@@ -146,21 +147,23 @@ static void compose_render_fragment(til_module_context_t *context, unsigned tick
 		}
 
 		ctxt->texture_fb.cleared = 0;
-		til_module_render(ctxt->texture.module_ctxt, ticks, &ctxt->texture_fb);
-
-		til_module_render(ctxt->layers[0].module_ctxt, ticks, fragment);
+		/* XXX: if when snapshotting becomes a thing, ctxt->texture_fb is snapshottable, this will likely break as-is */
+		til_module_render(ctxt->texture.module_ctxt, ticks, &texture);
+		til_module_render(ctxt->layers[0].module_ctxt, ticks, &fragment);
 
 		for (size_t i = 1; i < ctxt->n_layers; i++) {
-			til_fb_fragment_t	textured = *fragment;
-
-			textured.texture = &ctxt->texture_fb;
+			til_fb_fragment_t	*old_texture = fragment->texture;
 
-			til_module_render(ctxt->layers[i].module_ctxt, ticks, &textured);
+			fragment->texture = texture;
+			til_module_render(ctxt->layers[i].module_ctxt, ticks, &fragment);
+			fragment->texture = old_texture;
 		}
 	} else {
 		for (size_t i = 0; i < ctxt->n_layers; i++)
-			til_module_render(ctxt->layers[i].module_ctxt, ticks, fragment);
+			til_module_render(ctxt->layers[i].module_ctxt, ticks, &fragment);
 	}
+
+	*fragment_ptr = fragment;
 }
 
 
diff --git a/src/modules/drizzle/drizzle.c b/src/modules/drizzle/drizzle.c
index ec97d16..fff59bd 100644
--- a/src/modules/drizzle/drizzle.c
+++ b/src/modules/drizzle/drizzle.c
@@ -106,7 +106,7 @@ static void drizzle_destroy_context(til_module_context_t *context)
 }
 
 
-static void drizzle_prepare_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t *fragment, til_frame_plan_t *res_frame_plan)
+static void drizzle_prepare_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t **fragment_ptr, til_frame_plan_t *res_frame_plan)
 {
 	drizzle_context_t	*ctxt = (drizzle_context_t *)context;
 
@@ -130,9 +130,11 @@ static void drizzle_prepare_frame(til_module_context_t *context, unsigned ticks,
 }
 
 
-static void drizzle_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t *fragment)
+static void drizzle_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t **fragment_ptr)
 {
 	drizzle_context_t	*ctxt = (drizzle_context_t *)context;
+	til_fb_fragment_t	*fragment = *fragment_ptr;
+
 	float			xf = 1.f / (float)fragment->frame_width;
 	float			yf = 1.f / (float)fragment->frame_height;
 	v2f_t			coord;
diff --git a/src/modules/flui2d/flui2d.c b/src/modules/flui2d/flui2d.c
index cb249c3..5272e4d 100644
--- a/src/modules/flui2d/flui2d.c
+++ b/src/modules/flui2d/flui2d.c
@@ -273,10 +273,12 @@ static til_module_context_t * flui2d_create_context(unsigned seed, unsigned tick
 
 
 /* Prepare a frame for concurrent drawing of fragment using multiple fragments */
-static void flui2d_prepare_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t *fragment, til_frame_plan_t *res_frame_plan)
+static void flui2d_prepare_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t **fragment_ptr, til_frame_plan_t *res_frame_plan)
 {
 	flui2d_context_t	*ctxt = (flui2d_context_t *)context;
-	float			r = (ticks % (unsigned)(2 * M_PI * 1000)) * .001f;
+	til_fb_fragment_t	*fragment = *fragment_ptr;
+
+	float	r = (ticks % (unsigned)(2 * M_PI * 1000)) * .001f;
 
 	*res_frame_plan = (til_frame_plan_t){ .fragmenter = til_fragmenter_tile64 };
 
@@ -332,9 +334,10 @@ static void flui2d_prepare_frame(til_module_context_t *context, unsigned ticks,
 
 
 /* Draw a the flui2d densities */
-static void flui2d_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t *fragment)
+static void flui2d_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t **fragment_ptr)
 {
 	flui2d_context_t	*ctxt = (flui2d_context_t *)context;
+	til_fb_fragment_t	*fragment = *fragment_ptr;
 
 	for (int y = fragment->y; y < fragment->y + fragment->height; y++) {
 		int	y0, y1;
diff --git a/src/modules/julia/julia.c b/src/modules/julia/julia.c
index aa05dd8..2668061 100644
--- a/src/modules/julia/julia.c
+++ b/src/modules/julia/julia.c
@@ -106,7 +106,7 @@ static inline unsigned julia_iter(float real, float imag, float creal, float cim
 
 
 /* Prepare a frame for concurrent drawing of fragment using multiple fragments */
-static void julia_prepare_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t *fragment, til_frame_plan_t *res_frame_plan)
+static void julia_prepare_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t **fragment_ptr, til_frame_plan_t *res_frame_plan)
 {
 	julia_context_t	*ctxt = (julia_context_t *)context;
 
@@ -133,9 +133,11 @@ static void julia_prepare_frame(til_module_context_t *context, unsigned ticks, t
 
 
 /* Draw a morphing Julia set */
-static void julia_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t *fragment)
+static void julia_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t **fragment_ptr)
 {
-	julia_context_t	*ctxt = (julia_context_t *)context;
+	julia_context_t		*ctxt = (julia_context_t *)context;
+	til_fb_fragment_t	*fragment = *fragment_ptr;
+
 	unsigned	x, y;
 	unsigned	width = fragment->width, height = fragment->height;
 	uint32_t	*buf = fragment->buf;
diff --git a/src/modules/meta2d/meta2d.c b/src/modules/meta2d/meta2d.c
index b7b6708..8af3981 100644
--- a/src/modules/meta2d/meta2d.c
+++ b/src/modules/meta2d/meta2d.c
@@ -101,7 +101,7 @@ static void meta2d_destroy_context(til_module_context_t *context)
 }
 
 
-static void meta2d_prepare_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t *fragment, til_frame_plan_t *res_frame_plan)
+static void meta2d_prepare_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t **fragment_ptr, til_frame_plan_t *res_frame_plan)
 {
 	meta2d_context_t	*ctxt = (meta2d_context_t *)context;
 
@@ -178,12 +178,14 @@ static void meta2d_prepare_frame(til_module_context_t *context, unsigned ticks,
 }
 
 
-static void meta2d_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t *fragment)
+static void meta2d_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t **fragment_ptr)
 {
 	meta2d_context_t	*ctxt = (meta2d_context_t *)context;
-	float			xf = 2.f / (float)fragment->frame_width;
-	float			yf = 2.f / (float)fragment->frame_height;
-	v2f_t			coord;
+	til_fb_fragment_t	*fragment = *fragment_ptr;
+
+	float	xf = 2.f / (float)fragment->frame_width;
+	float	yf = 2.f / (float)fragment->frame_height;
+	v2f_t	coord;
 
 	for (int y = fragment->y; y < fragment->y + fragment->height; y++) {
 		coord.y = yf * (float)y - 1.f;
diff --git a/src/modules/moire/moire.c b/src/modules/moire/moire.c
index ceeefe0..d528f8c 100644
--- a/src/modules/moire/moire.c
+++ b/src/modules/moire/moire.c
@@ -71,7 +71,7 @@ static til_module_context_t * moire_create_context(unsigned seed, unsigned ticks
 }
 
 
-static void moire_prepare_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t *fragment, til_frame_plan_t *res_frame_plan)
+static void moire_prepare_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t **fragment_ptr, til_frame_plan_t *res_frame_plan)
 {
 	moire_context_t	*ctxt = (moire_context_t *)context;
 
@@ -84,12 +84,14 @@ static void moire_prepare_frame(til_module_context_t *context, unsigned ticks, t
 }
 
 
-static void moire_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t *fragment)
+static void moire_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t **fragment_ptr)
 {
-	moire_context_t	*ctxt = (moire_context_t *)context;
-	float		xf = 2.f / (float)fragment->frame_width;
-	float		yf = 2.f / (float)fragment->frame_height;
-	float		cx, cy;
+	moire_context_t		*ctxt = (moire_context_t *)context;
+	til_fb_fragment_t	*fragment = *fragment_ptr;
+
+	float	xf = 2.f / (float)fragment->frame_width;
+	float	yf = 2.f / (float)fragment->frame_height;
+	float	cx, cy;
 
 	/* TODO: optimize */
 	cy = yf * (float)fragment->y - 1.f;
diff --git a/src/modules/montage/montage.c b/src/modules/montage/montage.c
index 7991e3f..eaf8be7 100644
--- a/src/modules/montage/montage.c
+++ b/src/modules/montage/montage.c
@@ -18,8 +18,8 @@ typedef struct montage_context_t {
 
 static til_module_context_t * montage_create_context(unsigned seed, unsigned ticks, unsigned n_cpus, til_setup_t *setup);
 static void montage_destroy_context(til_module_context_t *context);
-static void montage_prepare_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t *fragment, til_frame_plan_t *res_frame_plan);
-static void montage_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t *fragment);
+static void montage_prepare_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t **fragment_ptr, til_frame_plan_t *res_frame_plan);
+static void montage_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t **fragment_ptr);
 
 
 til_module_t	montage_module = {
@@ -184,15 +184,16 @@ static int montage_fragmenter(til_module_context_t *context, const til_fb_fragme
 }
 
 
-static void montage_prepare_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t *fragment, til_frame_plan_t *res_frame_plan)
+static void montage_prepare_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t **fragment_ptr, til_frame_plan_t *res_frame_plan)
 {
 	*res_frame_plan = (til_frame_plan_t){ .fragmenter = montage_fragmenter };
 }
 
 
-static void montage_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t *fragment)
+static void montage_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t **fragment_ptr)
 {
 	montage_context_t	*ctxt = (montage_context_t *)context;
+	til_fb_fragment_t	*fragment = *fragment_ptr;
 
 	if (fragment->number >= ctxt->n_modules) {
 		til_fb_fragment_clear(fragment);
@@ -200,5 +201,5 @@ static void montage_render_fragment(til_module_context_t *context, unsigned tick
 		return;
 	}
 
-	til_module_render(ctxt->contexts[fragment->number], ticks, fragment);
+	til_module_render(ctxt->contexts[fragment->number], ticks, fragment_ptr);
 }
diff --git a/src/modules/pixbounce/pixbounce.c b/src/modules/pixbounce/pixbounce.c
index d200ad6..6a6bfb3 100644
--- a/src/modules/pixbounce/pixbounce.c
+++ b/src/modules/pixbounce/pixbounce.c
@@ -260,9 +260,10 @@ static til_module_context_t * pixbounce_create_context(unsigned seed, unsigned t
 	return &ctxt->til_module_context;
 }
 
-static void pixbounce_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t *fragment)
+static void pixbounce_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t **fragment_ptr)
 {
-	pixbounce_context_t *ctxt = (pixbounce_context_t *)context;
+	pixbounce_context_t	*ctxt = (pixbounce_context_t *)context;
+	til_fb_fragment_t	*fragment = *fragment_ptr;
 
 	int	width = fragment->width, height = fragment->height;
 
diff --git a/src/modules/plasma/plasma.c b/src/modules/plasma/plasma.c
index 8cc4fda..b58e34f 100644
--- a/src/modules/plasma/plasma.c
+++ b/src/modules/plasma/plasma.c
@@ -75,7 +75,7 @@ static til_module_context_t * plasma_create_context(unsigned seed, unsigned tick
 
 
 /* Prepare a frame for concurrent drawing of fragment using multiple fragments */
-static void plasma_prepare_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t *fragment, til_frame_plan_t *res_frame_plan)
+static void plasma_prepare_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t **fragment_ptr, til_frame_plan_t *res_frame_plan)
 {
 	plasma_context_t	*ctxt = (plasma_context_t *)context;
 
@@ -85,17 +85,19 @@ static void plasma_prepare_frame(til_module_context_t *context, unsigned ticks,
 
 
 /* Draw a plasma effect */
-static void plasma_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t *fragment)
+static void plasma_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t **fragment_ptr)
 {
 	plasma_context_t	*ctxt = (plasma_context_t *)context;
-	int			xstep = PLASMA_WIDTH / fragment->frame_width;
-	int			ystep = PLASMA_HEIGHT / fragment->frame_height;
-	unsigned		width = fragment->width * xstep, height = fragment->height * ystep;
-	int			fw2 = FIXED_NEW(width / 2), fh2 = FIXED_NEW(height / 2);
-	int			x, y, cx, cy, dx2, dy2;
-	uint32_t		*buf = fragment->buf;
-	color_t			c = { .r = 0, .g = 0, .b = 0 }, cscale;
-	unsigned		rr2, rr6, rr8, rr16, rr20, rr12;
+	til_fb_fragment_t	*fragment = *fragment_ptr;
+
+	int		xstep = PLASMA_WIDTH / fragment->frame_width;
+	int		ystep = PLASMA_HEIGHT / fragment->frame_height;
+	unsigned	width = fragment->width * xstep, height = fragment->height * ystep;
+	int		fw2 = FIXED_NEW(width / 2), fh2 = FIXED_NEW(height / 2);
+	int		x, y, cx, cy, dx2, dy2;
+	uint32_t	*buf = fragment->buf;
+	color_t		c = { .r = 0, .g = 0, .b = 0 }, cscale;
+	unsigned	rr2, rr6, rr8, rr16, rr20, rr12;
 
 	rr2 = ctxt->rr * 2;
 	rr6 = ctxt->rr * 6;
diff --git a/src/modules/plato/plato.c b/src/modules/plato/plato.c
index 43d9bdd..f56bef8 100644
--- a/src/modules/plato/plato.c
+++ b/src/modules/plato/plato.c
@@ -622,9 +622,10 @@ static til_module_context_t * plato_create_context(unsigned seed, unsigned ticks
 }
 
 
-static void plato_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t *fragment)
+static void plato_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t **fragment_ptr)
 {
-	plato_context_t	*ctxt = (plato_context_t *)context;
+	plato_context_t		*ctxt = (plato_context_t *)context;
+	til_fb_fragment_t	*fragment = *fragment_ptr;
 
 	ctxt->r += (float)(ticks - context->ticks) * .001f;
 	context->ticks = ticks;
diff --git a/src/modules/ray/ray.c b/src/modules/ray/ray.c
index ead6636..9814dcc 100644
--- a/src/modules/ray/ray.c
+++ b/src/modules/ray/ray.c
@@ -145,9 +145,10 @@ static til_module_context_t * ray_create_context(unsigned seed, unsigned ticks,
 
 
 /* prepare a frame for concurrent rendering */
-static void ray_prepare_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t *fragment, til_frame_plan_t *res_frame_plan)
+static void ray_prepare_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t **fragment_ptr, til_frame_plan_t *res_frame_plan)
 {
-	ray_context_t	*ctxt = (ray_context_t *)context;
+	ray_context_t		*ctxt = (ray_context_t *)context;
+	til_fb_fragment_t	*fragment = *fragment_ptr;
 
 	*res_frame_plan = (til_frame_plan_t){ .fragmenter = til_fragmenter_tile64 };
 #if 1
@@ -177,15 +178,16 @@ static void ray_prepare_frame(til_module_context_t *context, unsigned ticks, til
 
 
 /* ray trace a simple scene into the fragment */
-static void ray_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t *fragment)
+static void ray_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t **fragment_ptr)
 {
-	ray_context_t	*ctxt = (ray_context_t *)context;
+	ray_context_t		*ctxt = (ray_context_t *)context;
+	til_fb_fragment_t	*fragment = *fragment_ptr;
 
 	ray_render_trace_fragment(ctxt->render, fragment);
 }
 
 
-static void ray_finish_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t *fragment)
+static void ray_finish_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t **fragment_ptr)
 {
 	ray_context_t	*ctxt = (ray_context_t *)context;
 
diff --git a/src/modules/roto/roto.c b/src/modules/roto/roto.c
index a8ee45d..e2abea3 100644
--- a/src/modules/roto/roto.c
+++ b/src/modules/roto/roto.c
@@ -174,7 +174,7 @@ static void init_roto(uint8_t texture[256][256], int32_t *costab, int32_t *sinta
 
 
 /* prepare a frame for concurrent rendering */
-static void roto_prepare_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t *fragment, til_frame_plan_t *res_frame_plan)
+static void roto_prepare_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t **fragment_ptr, til_frame_plan_t *res_frame_plan)
 {
 	roto_context_t	*ctxt = (roto_context_t *)context;
 	static int	initialized;
@@ -207,9 +207,11 @@ static void roto_prepare_frame(til_module_context_t *context, unsigned ticks, ti
 
 
 /* Draw a rotating checkered 256x256 texture into fragment. */
-static void roto_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t *fragment)
+static void roto_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t **fragment_ptr)
 {
-	roto_context_t	*ctxt = (roto_context_t *)context;
+	roto_context_t		*ctxt = (roto_context_t *)context;
+	til_fb_fragment_t	*fragment = *fragment_ptr;
+
 	int		x, y, frame_width = fragment->frame_width, frame_height = fragment->frame_height;
 	int		y_cos_r, y_sin_r, x_cos_r, x_sin_r, x_cos_r_init, x_sin_r_init, cos_r, sin_r;
 	uint32_t	*buf = fragment->buf;
diff --git a/src/modules/rtv/rtv.c b/src/modules/rtv/rtv.c
index 3a8e7fc..13c8da9 100644
--- a/src/modules/rtv/rtv.c
+++ b/src/modules/rtv/rtv.c
@@ -63,8 +63,8 @@ typedef struct rtv_setup_t {
 static void setup_next_channel(rtv_context_t *ctxt, unsigned ticks);
 static til_module_context_t * rtv_create_context(unsigned seed, unsigned ticks, unsigned n_cpus, til_setup_t *setup);
 static void rtv_destroy_context(til_module_context_t *context);
-static void rtv_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t *fragment);
-static void rtv_finish_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t *fragment);
+static void rtv_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t **fragment_ptr);
+static void rtv_finish_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t **fragment_ptr);
 static int rtv_setup(const til_settings_t *settings, til_setting_t **res_setting, const til_setting_desc_t **res_desc, til_setup_t **res_setup);
 
 static rtv_setup_t rtv_default_setup = {
@@ -268,7 +268,7 @@ static void rtv_destroy_context(til_module_context_t *context)
 }
 
 
-static void rtv_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t *fragment)
+static void rtv_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t **fragment_ptr)
 {
 	rtv_context_t	*ctxt = (rtv_context_t *)context;
 	time_t		now = time(NULL);
@@ -279,13 +279,14 @@ static void rtv_render_fragment(til_module_context_t *context, unsigned ticks, u
 	if (now >= ctxt->next_hide_caption)
 		ctxt->caption = NULL;
 
-	til_module_render(ctxt->channel->module_ctxt, ticks, fragment);
+	til_module_render(ctxt->channel->module_ctxt, ticks, fragment_ptr);
 }
 
 
-static void rtv_finish_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t *fragment)
+static void rtv_finish_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t **fragment_ptr)
 {
-	rtv_context_t	*ctxt = (rtv_context_t *)context;
+	rtv_context_t		*ctxt = (rtv_context_t *)context;
+	til_fb_fragment_t	*fragment = *fragment_ptr;
 
 	if (!ctxt->caption)
 		return;
diff --git a/src/modules/shapes/shapes.c b/src/modules/shapes/shapes.c
index 47bb8df..bce0a37 100644
--- a/src/modules/shapes/shapes.c
+++ b/src/modules/shapes/shapes.c
@@ -115,9 +115,11 @@ static til_module_context_t * shapes_create_context(unsigned seed, unsigned tick
 }
 
 
-static void shapes_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t *fragment)
+static void shapes_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t **fragment_ptr)
 {
 	shapes_context_t	*ctxt = (shapes_context_t *)context;
+	til_fb_fragment_t	*fragment = *fragment_ptr;
+
 	unsigned		size = MIN(fragment->frame_width, fragment->frame_height) * ctxt->setup.scale;
 	unsigned		xoff = (fragment->frame_width - size) >> 1;
 	unsigned		yoff = (fragment->frame_height - size) >> 1;
diff --git a/src/modules/snow/snow.c b/src/modules/snow/snow.c
index a367113..1a171ee 100644
--- a/src/modules/snow/snow.c
+++ b/src/modules/snow/snow.c
@@ -37,15 +37,17 @@ static til_module_context_t * snow_create_context(unsigned seed, unsigned ticks,
 }
 
 
-static void snow_prepare_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t *fragment, til_frame_plan_t *res_frame_plan)
+static void snow_prepare_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t **fragment_ptr, til_frame_plan_t *res_frame_plan)
 {
 	*res_frame_plan = (til_frame_plan_t){ .fragmenter = til_fragmenter_slice_per_cpu };
 }
 
 
-static void snow_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t *fragment)
+static void snow_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t **fragment_ptr)
 {
-	snow_context_t	*ctxt = (snow_context_t *)context;
+	snow_context_t		*ctxt = (snow_context_t *)context;
+	til_fb_fragment_t	*fragment = *fragment_ptr;
+
 	unsigned	*seed = &ctxt->seeds[cpu].seed;
 
 	for (unsigned y = fragment->y; y < fragment->y + fragment->height; y++) {
diff --git a/src/modules/sparkler/sparkler.c b/src/modules/sparkler/sparkler.c
index f0f2cb6..339e3e9 100644
--- a/src/modules/sparkler/sparkler.c
+++ b/src/modules/sparkler/sparkler.c
@@ -75,9 +75,10 @@ static void sparkler_destroy_context(til_module_context_t *context)
 }
 
 
-static void sparkler_prepare_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t *fragment, til_frame_plan_t *res_frame_plan)
+static void sparkler_prepare_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t **fragment_ptr, til_frame_plan_t *res_frame_plan)
 {
 	sparkler_context_t	*ctxt = (sparkler_context_t *)context;
+	til_fb_fragment_t	*fragment = *fragment_ptr;
 
 	*res_frame_plan = (til_frame_plan_t){ .fragmenter = til_fragmenter_slice_per_cpu };
 
@@ -91,9 +92,10 @@ static void sparkler_prepare_frame(til_module_context_t *context, unsigned ticks
 
 
 /* Render a 3D particle system */
-static void sparkler_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t *fragment)
+static void sparkler_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t **fragment_ptr)
 {
 	sparkler_context_t	*ctxt = (sparkler_context_t *)context;
+	til_fb_fragment_t	*fragment = *fragment_ptr;
 
 	if (!ctxt->setup.show_bsp_matches)
 		til_fb_fragment_clear(fragment);
diff --git a/src/modules/spiro/spiro.c b/src/modules/spiro/spiro.c
index 30e5f06..76b3a80 100644
--- a/src/modules/spiro/spiro.c
+++ b/src/modules/spiro/spiro.c
@@ -53,13 +53,13 @@ static til_module_context_t * spiro_create_context(unsigned seed, unsigned ticks
 	return &ctxt->til_module_context;
 }
 
-static void spiro_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t *fragment)
+static void spiro_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t **fragment_ptr)
 {
-	spiro_context_t	*ctxt = (spiro_context_t *)context;
+	spiro_context_t		*ctxt = (spiro_context_t *)context;
+	til_fb_fragment_t	*fragment = *fragment_ptr;
 
-	int		width = fragment->frame_width, height = fragment->frame_height;
-
-	int display_R, display_origin_x, display_origin_y;
+	int	width = fragment->frame_width, height = fragment->frame_height;
+	int	display_R, display_origin_x, display_origin_y;
 
 	/* Based on the fragment's dimensions, calculate the origin and radius of the fixed outer
 	circle, C0. */
diff --git a/src/modules/stars/stars.c b/src/modules/stars/stars.c
index 3a3f90f..8e6a5d0 100644
--- a/src/modules/stars/stars.c
+++ b/src/modules/stars/stars.c
@@ -109,9 +109,11 @@ static void stars_destroy_context(til_module_context_t *context)
 }
 
 
-static void stars_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t *fragment)
+static void stars_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t **fragment_ptr)
 {
-	stars_context_t	*ctxt = (stars_context_t *)context;
+	stars_context_t		*ctxt = (stars_context_t *)context;
+	til_fb_fragment_t	*fragment = *fragment_ptr;
+
 	struct points* iterator;
 	struct points* tmp_ptr;
 	struct points* last_ptr=NULL;
diff --git a/src/modules/submit/submit.c b/src/modules/submit/submit.c
index daac37b..5f46461 100644
--- a/src/modules/submit/submit.c
+++ b/src/modules/submit/submit.c
@@ -294,7 +294,7 @@ static void submit_destroy_context(til_module_context_t *context)
 }
 
 
-static void submit_prepare_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t *fragment, til_frame_plan_t *res_frame_plan)
+static void submit_prepare_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t **fragment_ptr, til_frame_plan_t *res_frame_plan)
 {
 	submit_context_t	*ctxt = (submit_context_t *)context;
 
@@ -317,9 +317,10 @@ static void submit_prepare_frame(til_module_context_t *context, unsigned ticks,
 }
 
 
-static void submit_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t *fragment)
+static void submit_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t **fragment_ptr)
 {
 	submit_context_t	*ctxt = (submit_context_t *)context;
+	til_fb_fragment_t	*fragment = *fragment_ptr;
 
 	if (!ctxt->bilerp)
 		draw_grid(ctxt, fragment);
diff --git a/src/modules/swab/swab.c b/src/modules/swab/swab.c
index 9047f68..6d1c3d9 100644
--- a/src/modules/swab/swab.c
+++ b/src/modules/swab/swab.c
@@ -93,7 +93,7 @@ static void swab_destroy_context(til_module_context_t *context)
 }
 
 
-static void swab_prepare_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t *fragment, til_frame_plan_t *res_frame_plan)
+static void swab_prepare_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t **fragment_ptr, til_frame_plan_t *res_frame_plan)
 {
 	swab_context_t	*ctxt = (swab_context_t *)context;
 
@@ -103,15 +103,17 @@ static void swab_prepare_frame(til_module_context_t *context, unsigned ticks, ti
 }
 
 
-static void swab_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t *fragment)
+static void swab_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t **fragment_ptr)
 {
-	swab_context_t	*ctxt = (swab_context_t *)context;
-	float		cos_r = cos(ctxt->r);
-	float		sin_r = sin(ctxt->r);
-	float		z1 = cos_r;
-	float		z2 = sin_r;
-	float		xscale = 1.f / (float)fragment->frame_width;
-	float		yscale = 1.f / (float)fragment->frame_height;
+	swab_context_t		*ctxt = (swab_context_t *)context;
+	til_fb_fragment_t	*fragment = *fragment_ptr;
+
+	float	cos_r = cos(ctxt->r);
+	float	sin_r = sin(ctxt->r);
+	float	z1 = cos_r;
+	float	z2 = sin_r;
+	float	xscale = 1.f / (float)fragment->frame_width;
+	float	yscale = 1.f / (float)fragment->frame_height;
 
 	for (int y = fragment->y; y < fragment->y + fragment->height; y++) {
 		float	yscaled = (float)y * yscale;
diff --git a/src/modules/swarm/swarm.c b/src/modules/swarm/swarm.c
index 0c58bf9..c896735 100644
--- a/src/modules/swarm/swarm.c
+++ b/src/modules/swarm/swarm.c
@@ -401,9 +401,10 @@ static void swarm_draw_as_lines(swarm_context_t *ctxt, til_fb_fragment_t *fragme
 }
 
 
-static void swarm_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t *fragment)
+static void swarm_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t **fragment_ptr)
 {
-	swarm_context_t	*ctxt = (swarm_context_t *)context;
+	swarm_context_t		*ctxt = (swarm_context_t *)context;
+	til_fb_fragment_t	*fragment = *fragment_ptr;
 
 	swarm_update(ctxt, ticks);
 
diff --git a/src/modules/voronoi/voronoi.c b/src/modules/voronoi/voronoi.c
index 8e9a0f3..2d1c8e5 100644
--- a/src/modules/voronoi/voronoi.c
+++ b/src/modules/voronoi/voronoi.c
@@ -281,9 +281,10 @@ static void voronoi_sample_colors(voronoi_context_t *ctxt, til_fb_fragment_t *fr
 }
 
 
-static void voronoi_prepare_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t *fragment, til_frame_plan_t *res_frame_plan)
+static void voronoi_prepare_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t **fragment_ptr, til_frame_plan_t *res_frame_plan)
 {
 	voronoi_context_t	*ctxt = (voronoi_context_t *)context;
+	til_fb_fragment_t	*fragment = *fragment_ptr;
 
 	*res_frame_plan = (til_frame_plan_t){ .fragmenter = til_fragmenter_tile64 };
 
@@ -314,9 +315,10 @@ static void voronoi_prepare_frame(til_module_context_t *context, unsigned ticks,
 }
 
 
-static void voronoi_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t *fragment)
+static void voronoi_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t **fragment_ptr)
 {
 	voronoi_context_t	*ctxt = (voronoi_context_t *)context;
+	til_fb_fragment_t	*fragment = *fragment_ptr;
 
 	for (int y = 0; y < fragment->height; y++) {
 		for (int x = 0; x < fragment->width; x++) {
diff --git a/src/til.c b/src/til.c
index 478d43e..1bc03b4 100644
--- a/src/til.c
+++ b/src/til.c
@@ -100,15 +100,15 @@ void til_shutdown(void)
 }
 
 
-static void _blank_prepare_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t *fragment, til_frame_plan_t *res_frame_plan)
+static void _blank_prepare_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t **fragment_ptr, til_frame_plan_t *res_frame_plan)
 {
 	*res_frame_plan = (til_frame_plan_t){ .fragmenter = til_fragmenter_slice_per_cpu };
 }
 
 
-static void _blank_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t *fragment)
+static void _blank_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t **fragment_ptr)
 {
-	til_fb_fragment_clear(fragment);
+	til_fb_fragment_clear(*fragment_ptr);
 }
 
 
@@ -162,21 +162,21 @@ void til_get_modules(const til_module_t ***res_modules, size_t *res_n_modules)
 }
 
 
-static void module_render_fragment(til_module_context_t *context, til_threads_t *threads, unsigned ticks, til_fb_fragment_t *fragment)
+static void module_render_fragment(til_module_context_t *context, til_threads_t *threads, unsigned ticks, til_fb_fragment_t **fragment_ptr)
 {
 	const til_module_t	*module;
 
 	assert(context);
 	assert(context->module);
 	assert(threads);
-	assert(fragment);
+	assert(fragment_ptr && *fragment_ptr);
 
 	module = context->module;
 
 	if (module->prepare_frame) {
 		til_frame_plan_t	frame_plan = {};
 
-		module->prepare_frame(context, ticks, fragment, &frame_plan);
+		module->prepare_frame(context, ticks, fragment_ptr, &frame_plan);
 
 		/* XXX: any module which provides prepare_frame() must return a frame_plan.fragmenter,
 		 * and provide render_fragment()
@@ -185,31 +185,31 @@ static void module_render_fragment(til_module_context_t *context, til_threads_t
 		assert(module->render_fragment);
 
 		if (context->n_cpus > 1) {
-			til_threads_frame_submit(threads, fragment, &frame_plan, module->render_fragment, context, ticks);
+			til_threads_frame_submit(threads, fragment_ptr, &frame_plan, module->render_fragment, context, ticks);
 			til_threads_wait_idle(threads);
 		} else {
 			unsigned		fragnum = 0;
-			til_fb_fragment_t	frag;
+			til_fb_fragment_t	frag, *frag_ptr = &frag;
 
-			while (frame_plan.fragmenter(context, fragment, fragnum++, &frag))
-				module->render_fragment(context, ticks, 0, &frag);
+			while (frame_plan.fragmenter(context, *fragment_ptr, fragnum++, &frag))
+				module->render_fragment(context, ticks, 0, &frag_ptr);
 		}
 	} else if (module->render_fragment)
-		module->render_fragment(context, ticks, 0, fragment);
+		module->render_fragment(context, ticks, 0, fragment_ptr);
 
 	if (module->finish_frame)
-		module->finish_frame(context, ticks, fragment);
+		module->finish_frame(context, ticks, fragment_ptr);
 
-	fragment->cleared = 1;
+	(*fragment_ptr)->cleared = 1;
 }
 
 
 /* This is a public interface to the threaded module rendering intended for use by
  * modules that wish to get the output of other modules for their own use.
  */
-void til_module_render(til_module_context_t *context, unsigned ticks, til_fb_fragment_t *fragment)
+void til_module_render(til_module_context_t *context, unsigned ticks, til_fb_fragment_t **fragment_ptr)
 {
-	module_render_fragment(context, til_threads, ticks, fragment);
+	module_render_fragment(context, til_threads, ticks, fragment_ptr);
 }
 
 
diff --git a/src/til.h b/src/til.h
index 7d0d637..5d19ea7 100644
--- a/src/til.h
+++ b/src/til.h
@@ -24,9 +24,9 @@ typedef struct til_knob_t til_knob_t;
 typedef struct til_module_t {
 	til_module_context_t *	(*create_context)(unsigned seed, unsigned ticks, unsigned n_cpus, til_setup_t *setup);
 	void			(*destroy_context)(til_module_context_t *context);
-	void			(*prepare_frame)(til_module_context_t *context, unsigned ticks, til_fb_fragment_t *fragment, til_frame_plan_t *res_frame_plan);
-	void			(*render_fragment)(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t *fragment);
-	void			(*finish_frame)(til_module_context_t *context, unsigned ticks, til_fb_fragment_t *fragment);
+	void			(*prepare_frame)(til_module_context_t *context, unsigned ticks, til_fb_fragment_t **fragment_ptr, til_frame_plan_t *res_frame_plan);
+	void			(*render_fragment)(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t **fragment_ptr);
+	void			(*finish_frame)(til_module_context_t *context, unsigned ticks, til_fb_fragment_t **fragment_ptr);
 	int			(*setup)(const til_settings_t *settings, til_setting_t **res_setting, const til_setting_desc_t **res_desc, til_setup_t **res_setup);
 	size_t			(*knobs)(til_module_context_t *context, til_knob_t **res_knobs);
 	char			*name;
@@ -40,7 +40,7 @@ void til_quiesce(void);
 void til_shutdown(void);
 const til_module_t * til_lookup_module(const char *name);
 void til_get_modules(const til_module_t ***res_modules, size_t *res_n_modules);
-void til_module_render(til_module_context_t *context, unsigned ticks, til_fb_fragment_t *fragment);
+void til_module_render(til_module_context_t *context, unsigned ticks, til_fb_fragment_t **fragment_ptr);
 int til_module_create_context(const til_module_t *module, unsigned seed, unsigned ticks, unsigned n_cpus, til_setup_t *setup, til_module_context_t **res_context);
 til_module_context_t * til_module_destroy_context(til_module_context_t *context);
 int til_module_setup(til_settings_t *settings, til_setting_t **res_setting, const til_setting_desc_t **res_desc, til_setup_t **res_setup);
diff --git a/src/til_threads.c b/src/til_threads.c
index af4de53..e2c8a97 100644
--- a/src/til_threads.c
+++ b/src/til_threads.c
@@ -22,9 +22,9 @@ typedef struct til_threads_t {
 
 	pthread_mutex_t		frame_mutex;
 	pthread_cond_t		frame_cond;
-	void			(*render_fragment_func)(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t *fragment);
+	void			(*render_fragment_func)(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t **fragment_ptr);
 	void			*context;
-	til_fb_fragment_t	*fragment;
+	til_fb_fragment_t	**fragment_ptr;
 	til_frame_plan_t	frame_plan;
 	unsigned		ticks;
 
@@ -63,27 +63,27 @@ static void * thread_func(void *_thread)
 			 * which may require a consistent mapping of CPU to fragnum across frames.
 			 */
 			for (;;) {
-				til_fb_fragment_t	fragment;
+				til_fb_fragment_t	frag, *frag_ptr = &frag;
 
 				while (!__sync_bool_compare_and_swap(&threads->next_fragment, frag_num, frag_num + 1));
 
-				if (!threads->frame_plan.fragmenter(threads->context, threads->fragment, frag_num, &fragment))
+				if (!threads->frame_plan.fragmenter(threads->context, *(threads->fragment_ptr), frag_num, &frag))
 					break;
 
-				threads->render_fragment_func(threads->context, threads->ticks, thread->id, &fragment);
+				threads->render_fragment_func(threads->context, threads->ticks, thread->id, &frag_ptr);
 				frag_num += threads->n_threads;
 			}
 		} else { /* render *any* available fragment */
 			for (;;) {
 				unsigned		frag_num;
-				til_fb_fragment_t	fragment;
+				til_fb_fragment_t	frag, *frag_ptr = &frag;
 
 				frag_num = __sync_fetch_and_add(&threads->next_fragment, 1);
 
-				if (!threads->frame_plan.fragmenter(threads->context, threads->fragment, frag_num, &fragment))
+				if (!threads->frame_plan.fragmenter(threads->context, *(threads->fragment_ptr), frag_num, &frag))
 					break;
 
-				threads->render_fragment_func(threads->context, threads->ticks, thread->id, &fragment);
+				threads->render_fragment_func(threads->context, threads->ticks, thread->id, &frag_ptr);
 			}
 		}
 
@@ -112,13 +112,13 @@ void til_threads_wait_idle(til_threads_t *threads)
 
 
 /* submit a frame's fragments to the threads */
-void til_threads_frame_submit(til_threads_t *threads, til_fb_fragment_t *fragment, til_frame_plan_t *frame_plan, void (*render_fragment_func)(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t *fragment), til_module_context_t *context, unsigned ticks)
+void til_threads_frame_submit(til_threads_t *threads, til_fb_fragment_t **fragment_ptr, til_frame_plan_t *frame_plan, void (*render_fragment_func)(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t **fragment_ptr), til_module_context_t *context, unsigned ticks)
 {
 	til_threads_wait_idle(threads);	/* XXX: likely non-blocking; already happens pre page flip */
 
 	pthread_mutex_lock(&threads->frame_mutex);
 	pthread_cleanup_push((void (*)(void *))pthread_mutex_unlock, &threads->frame_mutex);
-	threads->fragment = fragment;
+	threads->fragment_ptr = fragment_ptr;
 	threads->frame_plan = *frame_plan;
 	threads->render_fragment_func = render_fragment_func;
 	threads->context = context;
diff --git a/src/til_threads.h b/src/til_threads.h
index 329ead9..4e6836d 100644
--- a/src/til_threads.h
+++ b/src/til_threads.h
@@ -7,7 +7,7 @@ typedef struct til_threads_t til_threads_t;
 til_threads_t * til_threads_create();
 void til_threads_destroy(til_threads_t *threads);
 
-void til_threads_frame_submit(til_threads_t *threads, til_fb_fragment_t *fragment, til_frame_plan_t *frame_plan, void (*render_fragment_func)(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t *fragment), til_module_context_t *context, unsigned ticks);
+void til_threads_frame_submit(til_threads_t *threads, til_fb_fragment_t **fragment_ptr, til_frame_plan_t *frame_plan, void (*render_fragment_func)(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t **fragment_ptr), til_module_context_t *context, unsigned ticks);
 void til_threads_wait_idle(til_threads_t *threads);
 unsigned til_threads_num_threads(til_threads_t *threads);