add an example of how read a soundfont from memory

doc/fluidsynth-v11-devdoc.txt

@@ -98,7 +98,7 @@ Changes in FluidSynth 2.0.0 concerning developers:
 - add individual reverb setters: fluid_synth_set_reverb_roomsize(), fluid_synth_set_reverb_damp(), fluid_synth_set_reverb_width(), fluid_synth_set_reverb_level()
 - add individual chorus setters: fluid_synth_set_chorus_nr(), fluid_synth_set_chorus_level(), fluid_synth_set_chorus_speed(), fluid_synth_set_chorus_depth(), fluid_synth_set_chorus_type()
 - introduce a separate data type for sequencer client IDs: #fluid_seq_id_t
-- add file callback struct to _fluid_sfloader_t and expose new_fluid_defsfloader() to enable soundfont loading from memory
+- add file callback struct to _fluid_sfloader_t and expose new_fluid_defsfloader() to enable soundfont loading from memory ( see fluid_sfload_mem.c )
 
 
 \section NewIn1_1_9 Whats new in 1.1.9?
@@ -797,3 +797,8 @@ Example of an arpeggio generated using the MIDI sequencer API
 \example fluidsynth_register_adriver.c
 Example of how to register audio drivers using fluid_audio_driver_register() (advanced users only)
 */
+
+/*!
+\example fluidsynth_sfload_mem.c
+Example of how read a soundfont from memory (advanced users only)
+*/

doc/fluidsynth_register_adriver.c

@@ -1,4 +1,4 @@
-/**
+/*
  * This is a simple C99 program that demonstrates the usage of fluid_audio_driver_register()
  * 
  * There are 3 calls to fluid_audio_driver_register(), i.e. 3 iterations:

doc/fluidsynth_sfload_mem.c

@@ -0,0 +1,95 @@
+/*
+ * This is a C99 program that demonstrates how to load a soundfont from memory.
+ * 
+ * It only gives a brief overview on how to achieve this with fluidsynth's API.
+ * Although it should compile, it's highly incomplete, as the details of it's
+ * implementation depend on the users needs.
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include <fluidsynth.h>
+
+void * my_open(const char * filename)
+{
+    void* p;
+    if(filename[0] != '&')
+    {
+        return NULL;
+    }
+    scanf("&%p", &p);
+    return p;
+}
+
+int my_read(void *buf, int count, void * handle)
+{
+    // not yet implemented
+    memset(buf, 0, count);
+    return FLUID_OK;
+}
+
+int my_seek(void * handle, long offset, int origin)
+{
+    // NYI
+    return FLUID_OK;
+}
+
+int my_close(void * handle)
+{
+    // NYI
+    return FLUID_OK;
+}
+
+long my_tell(void * handle)
+{
+    // NYI
+    return 0;
+}
+
+fluid_file_callbacks_t my_cb =
+{
+    .fopen = my_open,
+    .fread = my_read,
+    .fseek = my_seek,
+    .fclose = my_close,
+    .ftell = my_tell
+};
+
+int main()
+{
+    int err = 0;
+
+    fluid_settings_t* settings = new_fluid_settings();
+    fluid_synth_t* synth = new_fluid_synth(settings);
+    
+    fluid_sfloader_t* my_sfloader = new_fluid_defsfloader(settings);
+    my_sfloader->file_callbacks = &my_cb;
+    fluid_synth_add_sfloader(synth, my_sfloader);
+    
+    
+    char abused_filename[64];
+    const void* pointer_to_sf2_in_mem = 0x1234Beef; // some pointer to where the soundfont shall be loaded from
+    sprintf(abused_filename, "&%p", pointer_to_sf2_in_mem);
+    
+    int id = fluid_synth_sfload(synth, abused_filename, 0);
+    /* now my_open() will be called with abused_filename and should have opened the memory region */
+    
+    if(id == FLUID_FAILED)
+    {
+        puts("oops");
+        err = -1;
+        goto cleanup;
+    }
+
+    /*
+     * ~~~ Do your daily business here ~~~
+     */
+    
+cleanup:    
+    /* deleting the synth also deletes my_sfloader */
+    delete_fluid_synth(synth);
+    
+    delete_fluid_settings(settings);
+    
+    return err;
+}