COMMON: Introduce --debug-channels-only command line flag.

Many of our systems currently generate significant amount of debug
output on deeper levels. Now, when your engine is using Debug Channels,
you might want to show that debug information only, which is currently
not possible, as the generic output will be mixed in your output.

Alternative solution would be to implement possibility to specify
per-channel debug levels.

base/commandLine.cpp

@@ -97,6 +97,7 @@ static const char HELP_STRING[] =
 	"  -d, --debuglevel=NUM     Set debug verbosity level\n"
 	"  --debugflags=FLAGS       Enable engine specific debug flags\n"
 	"                           (separated by commas)\n"
+	"  --debug-channels-only    Show only the specified debug channels\n"
 	"  -u, --dump-scripts       Enable script dumping if a directory called 'dumps'\n"
 	"                           exists in the current directory\n"
 	"\n"
@@ -426,6 +427,9 @@ Common::String parseCommandLine(Common::StringMap &settings, int argc, const cha
 			DO_LONG_OPTION("debugflags")
 			END_OPTION
 
+			DO_LONG_OPTION_BOOL("debug-channels-only")
+			END_OPTION
+
 			DO_OPTION('e', "music-driver")
 			END_OPTION
 

base/main.cpp

@@ -391,6 +391,10 @@ extern "C" int scummvm_main(int argc, const char * const argv[]) {
 	} else if (ConfMan.hasKey("debugflags"))
 		specialDebug = ConfMan.get("debugflags");
 
+	if (settings.contains("debug-channels-only"))
+		gDebugChannelsOnly = true;
+
+
 	PluginManager::instance().init();
  	PluginManager::instance().loadAllPlugins(); // load plugins for cached plugin manager
 

common/debug.cpp

@@ -30,6 +30,7 @@
 
 // TODO: Move gDebugLevel into namespace Common.
 int gDebugLevel = -1;
+bool gDebugChannelsOnly = false;
 
 namespace Common {
 
@@ -137,6 +138,9 @@ static void debugHelper(const char *s, va_list va, bool caret = true) {
 void debug(const char *s, ...) {
 	va_list va;
 
+	if (gDebugChannelsOnly)
+		return;
+
 	va_start(va, s);
 	debugHelper(s, va);
 	va_end(va);
@@ -145,7 +149,7 @@ void debug(const char *s, ...) {
 void debug(int level, const char *s, ...) {
 	va_list va;
 
-	if (level > gDebugLevel)
+	if (level > gDebugLevel || gDebugChannelsOnly)
 		return;
 
 	va_start(va, s);
@@ -157,6 +161,9 @@ void debug(int level, const char *s, ...) {
 void debugN(const char *s, ...) {
 	va_list va;
 
+	if (gDebugChannelsOnly)
+		return;
+
 	va_start(va, s);
 	debugHelper(s, va, false);
 	va_end(va);
@@ -165,7 +172,7 @@ void debugN(const char *s, ...) {
 void debugN(int level, const char *s, ...) {
 	va_list va;
 
-	if (level > gDebugLevel)
+	if (level > gDebugLevel || gDebugChannelsOnly)
 		return;
 
 	va_start(va, s);

common/debug.h

@@ -118,6 +118,15 @@ void debugCN(uint32 debugChannels, const char *s, ...) GCC_PRINTF(2, 3);
  */
 extern int gDebugLevel;
 
+/**
+ * Specify if we want to show only the debug channels and suppress
+ * the non-channeled output.
+ *
+ * This option is useful when you want to have higher levels of channels
+ * visible without the noise from other subsystems or OSystem.
+ */
+extern bool gDebugChannelsOnly;
+
 //Global constant for EventRecorder debug channel
 enum GlobalDebugLevels {
 	kDebugLevelEventRec = 1 << 30