Add similar functions for controlling OPL volumes, just like what's

present for digitized sounds. This is still limited to SB Pro, SB 16.
Also add a compatibility macro related to Line-In for S3DNA.

src/backend/audio/be_audio_opl.c

@@ -54,6 +54,16 @@ void BEL_ST_SetOPLMixerSource(BE_ST_AudioMixerSource *src)
 	g_oplMixerSource = src;
 }
 
+void BE_ST_SetFMSBProSoundVolumes(uint8_t volBits)
+{
+	BEL_ST_SetSBProVolumesForSource(g_oplMixerSource, volBits);
+}
+
+uint8_t BE_ST_GetFMSBProSoundVolumes(void)
+{
+	return BEL_ST_GetSBProVolumesFromSource(g_oplMixerSource);
+}
+
 #define OPL_NUM_OF_SAMPLES 2048 // About 40ms of OPL sound data
 
 void BEL_ST_GenOPLSamples(BE_ST_SndSample_T *stream, int length)

src/be_st.h

@@ -313,6 +313,13 @@ void BE_ST_SetDigiSBProSoundVolumes(uint8_t volBits);
 // Same but for getting the volumes
 uint8_t BE_ST_GetDigiSBProSoundVolumes(void);
 
+// Similar functions, but for the SB Pro's FM synthesis.
+void BE_ST_SetFMSBProSoundVolumes(uint8_t volBits);
+uint8_t BE_ST_GetFMSBProSoundVolumes(void);
+
+// Compatibility macro that was originally added for Super 3-D Noah's Ark
+#define BE_ST_SetLineInSBProSoundVolumes(volBits)
+
 void BE_ST_PlaySoundEffect(void *data, int numOfSamples, int bits);
 void BE_ST_StopSoundEffect(void);
 // Safe alternatives for Borland's sound and nosound functions from Catacomb Abyss' gelib.c