modules/strobe: add rudimentary strobe light module

After reading about the Dreamachine[0], I wanted to experience
this phenomenon.  The javascript-based web implementations
struggled to hold a steady 10Hz rate and would flicker like
crazy, so here we are.

Only setting right now is period=float_seconds, defaults to .1
for 10Hz.

One limitation in the current implementation is when the frame
rate can't keep up with the period the strobe will just stick on
without ever going off, because the period will always be
expired.  There should probably be a setting to force turning off
for at least one frame when it can't keep up.

[0] https://en.wikipedia.org/wiki/Dreamachine

2 files changed, 158 insertions, 0 deletions

diff --git a/src/modules/strobe/Makefile.am b/src/modules/strobe/Makefile.am
new file mode 100644
index 0000000..8bac057
--- /dev/null
+++ b/src/modules/strobe/Makefile.am
@@ -0,0 +1,3 @@
+noinst_LTLIBRARIES = libstrobe.la
+libstrobe_la_SOURCES = strobe.c
+libstrobe_la_CPPFLAGS = -I@top_srcdir@/src
diff --git a/src/modules/strobe/strobe.c b/src/modules/strobe/strobe.c
new file mode 100644
index 0000000..4616df4
--- /dev/null
+++ b/src/modules/strobe/strobe.c
@@ -0,0 +1,155 @@
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "til.h"
+#include "til_fb.h"
+#include "til_module_context.h"
+
+/* Dead-simple strobe light, initially made to try simulate this contraption:
+ * https://en.wikipedia.org/wiki/Dreamachine
+ *
+ * But it might actually have some general utility in compositing.
+ */
+
+/* Copyright (C) 2022 Vito Caputo <vcaputo@pengaru.com> */
+
+/* TODO:
+ *	- Make period setting more flexible
+ *	- Currently if the frame rate can't keep up with the period, strobe will
+ *	  just stick on.  There should probably be a force_flash={yes,no} setting
+ *	  to ensure a flash still occurs when the frame rate can't keep up.
+ */
+
+#define	STROBE_DEFAULT_PERIOD		.1
+
+typedef struct strobe_setup_t {
+	til_setup_t		til_setup;
+	float			period;
+} strobe_setup_t;
+
+typedef struct strobe_context_t {
+	til_module_context_t	til_module_context;
+	strobe_setup_t		setup;
+	unsigned		ticks;
+	unsigned		flash:1;
+} strobe_context_t;
+
+
+static strobe_setup_t strobe_default_setup = {
+	.period = STROBE_DEFAULT_PERIOD,
+};
+
+
+static til_module_context_t * strobe_create_context(unsigned seed, unsigned ticks, unsigned n_cpus, til_setup_t *setup)
+{
+	strobe_context_t	*ctxt;
+
+	if (!setup)
+		setup = &strobe_default_setup.til_setup;
+
+	ctxt = til_module_context_new(sizeof(strobe_context_t), seed, ticks, n_cpus);
+	if (!ctxt)
+		return NULL;
+
+	ctxt->setup = *(strobe_setup_t *)setup;
+	ctxt->ticks = ticks;
+
+	return &ctxt->til_module_context;
+}
+
+
+static void strobe_prepare_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t **fragment_ptr, til_frame_plan_t *res_frame_plan)
+{
+	strobe_context_t	*ctxt = (strobe_context_t *)context;
+
+	*res_frame_plan = (til_frame_plan_t){ .fragmenter = til_fragmenter_slice_per_cpu };
+
+	if (ticks - ctxt->ticks >= (unsigned)(ctxt->setup.period * 1000.f))
+		ctxt->flash = 1;
+}
+
+
+static void strobe_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t **fragment_ptr)
+{
+	strobe_context_t	*ctxt = (strobe_context_t *)context;
+	til_fb_fragment_t	*fragment = *fragment_ptr;
+
+	if (!ctxt->flash)
+		return til_fb_fragment_clear(fragment);
+
+	til_fb_fragment_fill(fragment, TIL_FB_DRAW_FLAG_TEXTURABLE, 0xffffffff);
+}
+
+
+static void strobe_finish_frame(til_module_context_t *context, unsigned int ticks, til_fb_fragment_t **fragment_ptr)
+{
+	strobe_context_t	*ctxt = (strobe_context_t *)context;
+
+	if (!ctxt->flash)
+		return;
+
+	ctxt->flash = 0;
+	ctxt->ticks = ticks;
+}
+
+
+static int strobe_setup(const til_settings_t *settings, til_setting_t **res_setting, const til_setting_desc_t **res_desc, til_setup_t **res_setup)
+{
+	const char	*period;
+	const char	*period_values[] = {
+				".0166",
+				".02",
+				".025",
+				".05",
+				".1",
+				".25",
+				".5",
+				"1",
+				NULL
+			};
+	int		r;
+
+	r = til_settings_get_and_describe_value(settings,
+						&(til_setting_desc_t){
+							.name = "Strobe period",
+							.key = "period",
+							.regex = "\\.[0-9]+",
+							.preferred = TIL_SETTINGS_STR(STROBE_DEFAULT_PERIOD),
+							.values = period_values,
+							.annotations = NULL
+						},
+						&period,
+						res_setting,
+						res_desc);
+	if (r)
+		return r;
+
+	if (res_setup) {
+		strobe_setup_t	*setup;
+
+		setup = til_setup_new(sizeof(*setup), (void(*)(til_setup_t *))free);
+		if (!setup)
+			return -ENOMEM;
+
+		sscanf(period, "%f", &setup->period);
+
+		*res_setup = &setup->til_setup;
+	}
+
+	return 0;
+}
+
+
+til_module_t	strobe_module = {
+	.create_context = strobe_create_context,
+	.prepare_frame = strobe_prepare_frame,
+	.render_fragment = strobe_render_fragment,
+	.finish_frame = strobe_finish_frame,
+	.setup = strobe_setup,
+	.name = "strobe",
+	.description = "Strobe light (threaded)",
+	.author = "Vito Caputo <vcaputo@pengaru.com>",
+	.flags = TIL_MODULE_OVERLAYABLE,
+};