Add option for disabling all input (view-only mode) in streaming session

* By default this option is set to `false` and can be enabled using the
  new `-viewonly`/`viewonly` command-line/config options.
* When enabled, none of the input modules will be initialised, making
  the streaming session view-only, i.e. no input is sent to host.

To facilitate implementation, SDL initialisation with `sdl_init()` was moved
a bit earlier in the code to decouple from input initialisation.

docs/README.pod

@@ -149,6 +149,10 @@ Try streaming if GFE version or options are unsupported
 
 Send quit app request to remote after quitting session
 
+=item B<-viewonly>
+
+Disable all input processing (view-only mode)
+
 =item B<-verbose>
 
 Enable verbose output

moonlight.conf

@@ -43,6 +43,9 @@
 ## Send quit app request to remote after quitting session
 #quitappafter = false
 
+## Disable all input processing (view-only mode)
+#viewonly = false
+
 ## Select audio device to play sound on
 #audio = sysdefault
 

src/config.c

@@ -66,6 +66,7 @@ static struct option long_options[] = {
   {"codec", required_argument, NULL, 'x'},
   {"unsupported", no_argument, NULL, 'y'},
   {"quitappafter", no_argument, NULL, '1'},
+  {"viewonly", no_argument, NULL, '2'},
   {"verbose", no_argument, NULL, 'z'},
   {"debug", no_argument, NULL, 'Z'},
   {0, 0, 0, 0},
@@ -216,6 +217,9 @@ static void parse_argument(int c, char* value, PCONFIGURATION config) {
   case '1':
     config->quitappafter = true;
     break;
+  case '2':
+    config->viewonly = true;
+    break;
   case 'z':
     config->debug_level = 1;
     break;
@@ -289,6 +293,8 @@ void config_save(char* filename, PCONFIGURATION config) {
     write_config_bool(fd, "localaudio", config->localaudio);
   if (config->quitappafter)
     write_config_bool(fd, "quitappafter", config->quitappafter);
+  if (config->viewonly)
+    write_config_bool(fd, "viewonly", config->viewonly);
 
   if (strcmp(config->app, "Steam") != 0)
     write_config_string(fd, "app", config->app);
@@ -320,6 +326,7 @@ void config_parse(int argc, char* argv[], PCONFIGURATION config) {
   config->fullscreen = true;
   config->unsupported = false;
   config->quitappafter = false;
+  config->viewonly = false;
   config->codec = CODEC_UNSPECIFIED;
 
   config->inputsCount = 0;

src/config.h

@@ -41,6 +41,7 @@ typedef struct _CONFIGURATION {
   bool fullscreen;
   bool unsupported;
   bool quitappafter;
+  bool viewonly;
   char* inputs[MAX_INPUTS];
   int inputsCount;
   enum codecs codec;

src/main.c

@@ -128,8 +128,10 @@ static void stream(PSERVER_DATA server, PCONFIGURATION config, enum platform sys
   LiStartConnection(&server->serverInfo, &config->stream, &connection_callbacks, platform_get_video(system), platform_get_audio(system, config->audio_device), NULL, drFlags, config->audio_device, 0);
 
   if (IS_EMBEDDED(system)) {
+    if (!config->viewonly)
       evdev_start();
     loop_main();
+    if (!config->viewonly)
       evdev_stop();
   }
   #ifdef HAVE_SDL
@@ -185,6 +187,7 @@ static void help() {
   printf("\t-platform <system>\tSpecify system used for audio, video and input: pi/imx/aml/rk/x11/x11_vdpau/sdl/fake (default auto)\n");
   printf("\t-unsupported\t\tTry streaming if GFE version or options are unsupported\n");
   printf("\t-quitappafter\t\tSend quit app request to remote after quitting session\n");
+  printf("\t-viewonly\t\tDisable all input processing (view-only mode)\n");
   #if defined(HAVE_SDL) || defined(HAVE_X11)
   printf("\n WM options (SDL and X11 only)\n\n");
   printf("\t-windowed\t\tDisplay screen in a window\n");
@@ -288,6 +291,15 @@ int main(int argc, char* argv[]) {
     }
     config.stream.supportsHevc = config.codec != CODEC_H264 && (config.codec == CODEC_HEVC || platform_supports_hevc(system));
 
+    #ifdef HAVE_SDL
+    if (system == SDL)
+      sdl_init(config.stream.width, config.stream.height, config.fullscreen);
+    #endif
+
+    if (config.viewonly) {
+      if (config.debug_level > 0)
+        printf("View-only mode enabled, no input will be sent to the host computer\n");
+    } else {
       if (IS_EMBEDDED(system)) {
         char* mapping_env = getenv("SDL_GAMECONTROLLERCONFIG");
         if (config.mapping == NULL && mapping_env == NULL) {
@@ -326,11 +338,11 @@ int main(int argc, char* argv[]) {
           exit(-1);
         }
 
-      sdl_init(config.stream.width, config.stream.height, config.fullscreen);
         sdlinput_init(config.mapping);
         rumble_handler = sdlinput_rumble;
       }
       #endif
+    }
 
     stream(&server, &config, system);
   } else if (strcmp("pair", config.action) == 0) {