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.

1 files changed, 51 insertions, 0 deletions

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",
+};