Add function API to set default mapping

- Add fluid_synth_mixer_reset_mapping() in fluid_synth.c.
- Add command resetchanmap in fluid_cmd.c.

include/fluidsynth/synth.h

@@ -397,6 +397,7 @@ FLUIDSYNTH_API int fluid_synth_mixer_set_mapping(fluid_synth_t *synth,
                          int chan_to_out, int out_from_chan,
                          int chan_to_fx,  int fx_from_chan,
                          int chanfx_to_out, int out_from_fx);
+FLUIDSYNTH_API int fluid_synth_mixer_reset_mapping(fluid_synth_t *synth, int chan);
 
 #ifdef __cplusplus
 }

src/bindings/fluid_cmd.c

@@ -194,6 +194,10 @@ static const fluid_cmd_t fluid_commands[] =
         "chanmap", "mixer", fluid_handle_chanmap,
         "chanmap [chan1 chan2..]               Print mapping of all or some MIDI channels"
     },
+    {
+        "resetchanmap", "mixer", fluid_handle_resetchanmap,
+        "resetchanmap [chan1 chan2..]          Set default mapping of MIDI channels"
+    },
     {
         "setchanmapout", "mixer", fluid_handle_setchanmapout,
         "setchanmapout chan0 out0 [chan1 out1..] Set mapping MIDI channel to dry output"
@@ -3422,6 +3426,56 @@ int fluid_handle_chanmap(void *data, int ac, char **av,
     return 0;
 }
 
+/*-----------------------------------------------------------------------------
+ resetchanmap
+
+ With no parameter the command set default mapping for all MIDI channels.
+
+ resetchanmap chan0 [chan1 . . .]
+
+ Set default mapping for MIDI channels chan0 chan1 ..
+*/
+int fluid_handle_resetchanmap(void *data, int ac, char **av,
+                              fluid_ostream_t out)
+
+{
+    static const char name_cde[] = "resetchanmap";
+    FLUID_ENTRY_COMMAND(data);
+    fluid_synth_t *synth = handler->synth;
+
+    /* checks channels arguments: chan1 chan2 .... */
+    if(check_channels_arguments(ac, av, out, name_cde) < 0)
+    {
+        return -1;
+    }
+
+    if(ac)
+    {
+        /* resetchanmap chan0 [chan1 . . .] */
+        int i;
+
+        for(i = 0; i < ac; i++)
+        {
+            int chan = atoi(av[i]);
+            int result = fluid_synth_mixer_reset_mapping (synth, chan);
+
+            if(result == FLUID_FAILED)
+            {
+                fluid_ostream_printf(out, "%s: channel %3d, %s", name_cde, chan,
+                                     invalid_arg_msg);
+            }
+        }
+    }
+    else
+    {
+        /* set default mapping for all channels */
+        fluid_synth_mixer_reset_mapping(synth, -1);
+    }
+
+    /* prints result */
+    return fluid_handle_chanmap(data, 0, av, out);
+}
+
 /* type of MIDI channel mapping */
 enum channel_mapping_type
 {

src/bindings/fluid_cmd.h

@@ -104,6 +104,7 @@ int fluid_handle_setbreathmode(void *data, int ac, char **av, fluid_ostream_t ou
 int fluid_handle_sleep(void *data, int ac, char **av, fluid_ostream_t out);
 
 int fluid_handle_chanmap(void *data, int ac, char **av,fluid_ostream_t out);
+int fluid_handle_resetchanmap(void *data, int ac, char **av, fluid_ostream_t out);
 int fluid_handle_setchanmapout(void *data, int ac, char **av, fluid_ostream_t out);
 int fluid_handle_setchanmapfx(void *data, int ac, char **av, fluid_ostream_t out);
 int fluid_handle_setchanfxmapout(void *data, int ac, char **av, fluid_ostream_t out);

src/synth/fluid_synth.c

@@ -7599,3 +7599,74 @@ fluid_synth_mixer_set_mapping(fluid_synth_t *synth,
 
     FLUID_API_RETURN(FLUID_OK);
 }
+
+/**
+* Set mixer MIDI channel default mapping to audio buffers.
+* The default mapping are:
+*  (1) default MIDI channel mapping to audio dry buffers.
+*  (2) default MIDI channel mapping to fx unit input .
+*  (3) default unit fx output mapping to audio dry buffers.
+*
+* The function allows to set default mapping (1)(2) and (3)
+* for channel chan.
+* 1) set default mapping between MIDI channel chan and audio dry
+*    output index out_from_chan:
+*    out_from_chan = chan % synth.audio-groups.
+*
+* 2) set default mapping between MIDI channel chan and
+*    fx unit input index fx_from_chan:
+*    fx_from_chan = chan % synth.effects-groups.
+*
+* 3) set default mapping between fx unit fxunit_idx (which is mapped to chan)
+*    and audio dry output index out_from_fx:
+*    out_from_fx = fxunit_idx % synth.audio-groups.
+*
+* @param synth FluidSynth instance.
+* @param chan, MIDI channel to set default mapping to.
+*  Must be in the range (-1 to MIDI channel count - 1).
+*  If -1, all MIDI channels are set to default mapping.
+*
+* @return #FLUID_OK on success, #FLUID_FAILED otherwise
+*/
+int
+fluid_synth_mixer_reset_mapping(fluid_synth_t *synth, int chan)
+{
+    int nbr_chan;
+
+    fluid_return_val_if_fail(synth != NULL, FLUID_FAILED);
+    fluid_synth_api_enter(synth);
+
+    /* check parameters first */
+    if(chan < 0)
+    {
+        /* The range is all MIDI channels from 0 to MIDI channel count -1 */
+        chan = 0; /* beginning chan */
+        nbr_chan =  synth->midi_channels; /* MIDI Channels number */
+    }
+    else
+    {
+        if(chan >= synth->midi_channels)
+        {
+            FLUID_API_RETURN(FLUID_FAILED);
+        }
+
+        /* The range is only chan */
+        nbr_chan = chan + 1;
+    }
+
+    /* now set the default mapping */
+    for(; chan < nbr_chan; chan++)
+    {
+        int fxunit_idx = chan % synth->effects_groups;
+        synth->channel[chan]->mapping_to_out = chan % synth->audio_groups;
+        synth->channel[chan]->mapping_to_fx = fxunit_idx;
+       /* default mapping between fxunit_idx (which is mapped to chan)
+          and audio dry output.
+       */
+       fluid_rvoice_mixer_set_fx_out_mapping(synth->eventhandler->mixer,
+                                             fxunit_idx,
+                                             fxunit_idx % synth->audio_groups);
+    }
+
+    FLUID_API_RETURN(FLUID_OK);
+}