Let it take a command to run in its DISPLAY after "--".

src/main.cpp

@@ -32,6 +32,8 @@ bool g_bFilterGameWindow = true;
 
 bool g_bBorderlessOutputWindow = false;
 
+uint32_t g_nSubCommandArg = 0;
+
 int BIsNested()
 {
 	return g_bIsNested == true;
@@ -39,6 +41,17 @@ int BIsNested()
 
 int main(int argc, char **argv)
 {
+	// Grab the starting position of a potential command that follows "--" in argv
+	// Do it before getopt can reorder anything, for use later
+	for ( int i = 0; i < argc; i++ )
+	{
+		if ( strcmp( "--", argv[ i ] ) == 0 && i + 1 < argc )
+		{
+			g_nSubCommandArg = i + 1;
+			break;
+		}
+	}
+
 	int o;
 	ac = argc;
 	av = argv;

src/main.hpp

@@ -33,6 +33,8 @@ extern uint32_t g_nOutputHeight;
 
 extern bool g_bFilterGameWindow;
 
+extern uint32_t g_nSubCommandArg;
+
 int BIsNested( void );
 
 #ifndef C_SIDE

src/steamcompmgr.c

@@ -41,6 +41,9 @@
 #include <time.h>
 #include <unistd.h>
 #include <getopt.h>
+#include <spawn.h>
+#include <signal.h>
+
 #include <X11/Xlib.h>
 #include <X11/Xutil.h>
 #include <X11/Xatom.h>
@@ -60,6 +63,8 @@
 #define GPUVIS_TRACE_IMPLEMENTATION
 #include "gpuvis_trace_utils.h"
 
+extern char **environ;
+
 typedef struct _ignore {
 	struct _ignore	*next;
 	unsigned long	sequence;
@@ -1702,7 +1707,7 @@ steamcompmgr_main (int argc, char **argv)
 				break;
 		}
 	}
-	
+
 	dpy = XOpenDisplay (wlserver.wlr.xwayland->display_name);
 	if (!dpy)
 	{
@@ -1832,6 +1837,22 @@ steamcompmgr_main (int argc, char **argv)
 		readyPipeFD = -1;
 	}
 	
+	if ( g_nSubCommandArg != 0 )
+	{
+		pid_t pid;
+		
+		sigset_t fullset;
+		sigfillset( &fullset );
+		
+		posix_spawnattr_t attr;
+		
+		posix_spawnattr_init( &attr );
+		posix_spawnattr_setflags( &attr, POSIX_SPAWN_SETSIGDEF );
+		posix_spawnattr_setsigdefault( &attr, &fullset );
+		
+		posix_spawnp( &pid, argv[ g_nSubCommandArg ], NULL, &attr, &argv[ g_nSubCommandArg ], environ );
+	}
+	
 	for (;;)
 	{
 		focusDirty = False;