Implement reverse stereo option

The previous stable release of the player (xmp 3.5.0) had option -r
to reverse stereo channels. This option was temporarily removed during
libification to simplify the code base.

Reverse channels option was reimplemented by simply accepting negative
mixing parameters.

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>

src/common.h

@@ -14,6 +14,7 @@ struct options {
 	int dsp;		/* dsp effects */
 	int loop;		/* loop module */
 	int random;		/* play in random order */
+	int reverse;		/* reverse stereo channels */
 	int verbose;
 	int silent;		/* silent output */
 	int info;		/* display information and exit */

src/main.c

@@ -261,10 +261,6 @@ int main(int argc, char **argv)
 		setenv("XMP_INSTRUMENT_PATH", options.ins_path, 1);
 	}
 
-	if (options.mix >= 0) {
-		xmp_mixer_set(handle, XMP_MIXER_MIX, options.mix);
-	}
-
 	lf_flag = 0;
 	for (first = optind; optind < argc; optind++) {
 		if (options.verbose > 0) {
@@ -315,6 +311,15 @@ int main(int argc, char **argv)
 			xmp_mixer_set(handle, XMP_MIXER_INTERP, options.interp);
 			xmp_mixer_set(handle, XMP_MIXER_DSP, options.dsp);
 
+			if (options.mix >= 0) {
+				xmp_mixer_set(handle, XMP_MIXER_MIX, options.mix);
+			}
+
+			if (options.reverse) {
+				int mix = xmp_mixer_get(handle, XMP_MIXER_MIX);
+				xmp_mixer_set(handle, XMP_MIXER_MIX, -mix);
+			}
+
 			xmp_set_position(handle, options.start);
 
 			/* Mute channels */

src/options.c

@@ -83,6 +83,7 @@ static void usage(char *s)
 "   -F --nofilter          Disable IT lowpass filters\n"
 "   -o --output-file name  Mix the module to file ('-' for stdout)\n"
 "   -P --pan pan           Percentual pan separation\n"
+"   -r --reverse           Reverse left/right stereo channels\n"
 "   -u --unsigned          Set the mixer to use unsigned samples\n"
 "\nEnvironment options:\n"
 "   -I --instrument-path   Set pathname to external samples\n"
@@ -117,6 +118,7 @@ static struct option lopt[] = {
 	{ "load-only",		0, 0, OPT_LOADONLY },
 	{ "quiet",		0, 0, 'q' },
 	{ "random",		0, 0, 'R' },
+	{ "reverse",		0, 0, 'r' },
 	{ "solo",		1, 0, 'S' },
 	{ "start",		1, 0, 's' },
 	{ "stdout",		0, 0, 'c' },
@@ -133,7 +135,7 @@ void get_options(int argc, char **argv, struct options *options)
 	int optidx = 0;
 	int o;
 
-#define OPTIONS "a:b:cD:d:Ff:hI:i:LlM:mNo:P:qRS:s:T:t:uVv"
+#define OPTIONS "a:b:cD:d:Ff:hI:i:LlM:mNo:P:qRrS:s:T:t:uVv"
 	while ((o = getopt_long(argc, argv, OPTIONS, lopt, &optidx)) != -1) {
 		switch (o) {
 		case 'a':
@@ -225,6 +227,9 @@ void get_options(int argc, char **argv, struct options *options)
 		case 'R':
 			options->random = 1;
 			break;
+		case 'r':
+			options->reverse = 1;
+			break;
 		case 'M':
 		case 'S':
 			if (o == 'S') {