feat(video): slightly faster video acquisition with O_NONBLOCK

DEVELOPMENT.md

@@ -136,5 +136,4 @@ make -f Makefile.dev release-arch
   - [ ] Play from record text file
 - [ ] Fixes
   - [ ] Try to write NanoKontrol config
-  - [ ] Investigate video device fps loss (bad unregister ?)
-    -  explore libv4l directly [github](https://github.com/philips/libv4l) (with `-lv4l2`)
+  - [ ] Investigate video device fps loss (bad unregister ?)

src/forge.c

@@ -57,7 +57,7 @@ static void compute_fps(bool trace_fps) {
   }
 }
 
-static void init_context(const Parameters *params, unsigned int in_count) {
+static void init_context(const Parameters *params) {
   state_init(context, &project.state_config, params->demo, params->auto_random,
              params->auto_random_cycle, params->base_tempo, params->load_state);
 
@@ -66,14 +66,6 @@ static void init_context(const Parameters *params, unsigned int in_count) {
   memset(context->input_resolutions, 0, sizeof(context->input_resolutions));
   memset(context->input_formats, 0, sizeof(context->input_formats));
   memset(context->input_fps, 0, sizeof(context->input_fps));
-
-  for (unsigned int i = 0; i < in_count; i++) {
-    if (!inputs.values[i].error) {
-      context->input_resolutions[i][0] = inputs.values[i].width;
-      context->input_resolutions[i][1] = inputs.values[i].height;
-      context->input_formats[i] = inputs.values[i].pixelformat;
-    }
-  }
 }
 
 static void free_context() { shared_close_context(context); }
@@ -88,6 +80,12 @@ static void init_inputs(const StringArray *video_in, unsigned int video_size) {
 
   for (unsigned int i = 0; i < video_in->length; i++) {
     video_init(&inputs.values[i], video_in->values[i], video_size);
+
+    if (!inputs.values[i].error) {
+      context->input_resolutions[i][0] = inputs.values[i].width;
+      context->input_resolutions[i][1] = inputs.values[i].height;
+      context->input_formats[i] = inputs.values[i].pixelformat;
+    }
   }
 }
 
@@ -178,7 +176,7 @@ void forge_run(const Parameters *params) {
     return;
   }
 
-  init_context(params, project.in_count);
+  init_context(params);
 
 #ifdef VIDEO_IN
   init_inputs(&params->video_in, params->video_size);

src/video.c

@@ -74,7 +74,7 @@ static void open_device(VideoCapture *video_capture, const char *name) {
   video_capture->fd = -1;
   video_capture->exp_fd = -1;
 
-  video_capture->fd = open(name, O_RDWR);
+  video_capture->fd = open(name, O_RDWR | O_NONBLOCK);
   if (video_capture->fd == -1) {
     log_warn("(%s) Cannot open device", name);
     video_capture->error = true;
@@ -265,6 +265,8 @@ static void create_image_buffer(VideoCapture *video_capture) {
   video_capture->buf.memory = V4L2_MEMORY_MMAP;
   video_capture->buf.index = 0;
 
+  ioctl(video_capture->fd, VIDIOC_PREPARE_BUF);
+
   ioctl(video_capture->fd, VIDIOC_QBUF, &video_capture->buf);
 }
 
@@ -273,21 +275,13 @@ static void close_stream(const VideoCapture *video_capture) {
 }
 
 static bool read_video(VideoCapture *video_capture) {
-  if (ioctl(video_capture->fd, VIDIOC_DQBUF, &video_capture->buf) == -1) {
-    ioctl_error(video_capture, "VIDIOC_DQBUF",
-                "buffer type not supported or no buffer allocated or the index "
-                "is out of bounds");
-    return false;
-  }
+  bool result;
 
-  if (ioctl(video_capture->fd, VIDIOC_QBUF, &video_capture->buf) == -1) {
-    ioctl_error(video_capture, "VIDIOC_QBUF",
-                "buffer type not supported or no buffer allocated or the index "
-                "is out of bounds");
-    return false;
-  }
+  result = ioctl(video_capture->fd, VIDIOC_DQBUF, &video_capture->buf) != -1;
 
-  return true;
+  ioctl(video_capture->fd, VIDIOC_QBUF, &video_capture->buf);
+
+  return result;
 }
 
 void video_init(VideoCapture *video_capture, const char *name,
@@ -343,9 +337,8 @@ bool video_background_read(VideoCapture *video_capture, SharedContext *context,
            pid);
   timer_init(&timer, 30);
 
-  while (!context->stop && read_video(video_capture)) {
-    // repeat infinitely
-    if (timer_inc(&timer)) {
+  while (!context->stop) {
+    if (read_video(video_capture) && timer_inc(&timer)) {
       fps = timer_reset(&timer);
 
       context->input_fps[input_index] = (unsigned int)round(fps);