snow: add a simple tv snow / white noise module

I wanted to add some noise to the rtv module and figured why not
just add a snow module and make rtv pass through it briefly when
switching modules.

It's not interesting by itself, but as more composite/meta modules
like rtv get made it might be handy beyond rtv.

5 files changed, 58 insertions, 2 deletions

diff --git a/src/Makefile.am b/src/Makefile.am
index f6b4b92..74e12c2 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -4,4 +4,4 @@ rototiller_SOURCES = fb.c fb.h fps.c fps.h rototiller.c rototiller.h sdl_fb.c se
 if ENABLE_DRM
 rototiller_SOURCES += drm_fb.c
 endif
-rototiller_LDADD = modules/flui2d/libflui2d.a modules/julia/libjulia.a modules/pixbounce/libpixbounce.a modules/plasma/libplasma.a modules/ray/libray.a modules/roto/libroto.a modules/rtv/librtv.a modules/sparkler/libsparkler.a modules/stars/libstars.a modules/submit/libsubmit.a libs/grid/libgrid.a libs/ray/libray.a -lm
+rototiller_LDADD = modules/flui2d/libflui2d.a modules/julia/libjulia.a modules/pixbounce/libpixbounce.a modules/plasma/libplasma.a modules/ray/libray.a modules/roto/libroto.a modules/rtv/librtv.a modules/snow/libsnow.a modules/sparkler/libsparkler.a modules/stars/libstars.a modules/submit/libsubmit.a libs/grid/libgrid.a libs/ray/libray.a -lm
diff --git a/src/modules/Makefile.am b/src/modules/Makefile.am
index fa4e852..fa913a0 100644
--- a/src/modules/Makefile.am
+++ b/src/modules/Makefile.am
@@ -1 +1 @@
-SUBDIRS = flui2d julia pixbounce plasma ray roto rtv sparkler stars submit
+SUBDIRS = flui2d julia pixbounce plasma ray roto rtv snow sparkler stars submit
diff --git a/src/modules/snow/Makefile.am b/src/modules/snow/Makefile.am
new file mode 100644
index 0000000..73f767d
--- /dev/null
+++ b/src/modules/snow/Makefile.am
@@ -0,0 +1,3 @@
+noinst_LIBRARIES = libsnow.a
+libsnow_a_SOURCES = snow.c
+libsnow_a_CPPFLAGS = -I@top_srcdir@/src
diff --git a/src/modules/snow/snow.c b/src/modules/snow/snow.c
new file mode 100644
index 0000000..f3c20d5
--- /dev/null
+++ b/src/modules/snow/snow.c
@@ -0,0 +1,51 @@
+#include <stdint.h>
+#include <stdlib.h>
+#include <time.h>
+
+#include "fb.h"
+#include "rototiller.h"
+
+/* Copyright (C) 2019 - Vito Caputo <vcaputo@pengaru.com> */
+
+/* This implements white noise / snow just using rand() */
+
+/* To avoid the contention around rand() I'm just using rand_r()
+ * in an entirely racy fashion with a single seed from the threaded
+ * render_fragment().  It should really be per-cpu but the module
+ * api doesn't currently send down a cpu identifier to the render
+ * function, so TODO in the future add that.
+ */
+static int	snow_seed;
+
+static int snow_fragmenter(void *context, const fb_fragment_t *fragment, unsigned num, fb_fragment_t *res_fragment)
+{
+	return fb_fragment_slice_single(fragment, 32, num, res_fragment);
+}
+
+
+static void snow_prepare_frame(void *context, unsigned n_cpus, fb_fragment_t *fragment, rototiller_fragmenter_t *res_fragmenter)
+{
+	*res_fragmenter = snow_fragmenter;
+}
+
+
+static void snow_render_fragment(void *context, fb_fragment_t *fragment)
+{
+	for (unsigned y = fragment->y; y < fragment->y + fragment->height; y++) {
+		for (unsigned x = fragment->x; x < fragment->x + fragment->width; x++) {
+			uint32_t	pixel = rand_r(&snow_seed) % 256;
+
+			fb_fragment_put_pixel_unchecked(fragment, x, y, pixel << 16 | pixel << 8 | pixel);
+		}
+	}
+}
+
+
+rototiller_module_t	snow_module = {
+	.prepare_frame = snow_prepare_frame,
+	.render_fragment = snow_render_fragment,
+	.name = "snow",
+	.description = "TV snow / white noise",
+	.author = "Vito Caputo <vcaputo@pengaru.com>",
+	.license = "GPLv2",
+};
diff --git a/src/rototiller.c b/src/rototiller.c
index 51704a5..c8532af 100644
--- a/src/rototiller.c
+++ b/src/rototiller.c
@@ -38,6 +38,7 @@ extern rototiller_module_t	plasma_module;
 extern rototiller_module_t	roto_module;
 extern rototiller_module_t	ray_module;
 extern rototiller_module_t	rtv_module;
+extern rototiller_module_t	snow_module;
 extern rototiller_module_t	sparkler_module;
 extern rototiller_module_t	stars_module;
 extern rototiller_module_t	submit_module;
@@ -53,6 +54,7 @@ static const rototiller_module_t	*modules[] = {
 	&flui2d_module,
 	&pixbounce_module,
 	&rtv_module,
+	&snow_module,
 };
 
 typedef struct rototiller_t {