Add support for absolute transform (#1409)

Add support for absolute transform modulators

---------

Co-authored-by: derselbst <[email protected]>

doc/recent_changes.txt

@@ -5,6 +5,7 @@
 - synth.device-id now has a default value of 16
 - synth.gain now has a default value of 0.6
 - Default values of reverb and chorus settings have been tuned
+- fluid_mod_get_transform() and fluid_mod_set_transform() for SoundFont 2.04 compliant modulators
 
 \section NewIn2_3_2 What's new in 2.3.2?
 

include/fluidsynth/mod.h

@@ -57,6 +57,15 @@ enum fluid_mod_flags
     FLUID_MOD_SIN = 0x80,            /**< Custom non-standard sinus mapping function */
 };
 
+/**
+ * Transform types for the SoundFont2 modulators as defined by SoundFont 2.04 section 8.3.
+ */
+enum fluid_mod_transforms
+{
+    FLUID_MOD_TRANSFORM_LINEAR = 0, /**< Linear: directly add the computed value to summing node */
+    FLUID_MOD_TRANSFORM_ABS = 2     /**< Abs: add the absolute value of the computed to summing node */
+};
+
 /**
  * General controller (if #FLUID_MOD_GC in flags).  This
  * corresponds to SoundFont 2.04 PDF section 8.2.1
@@ -83,13 +92,15 @@ FLUIDSYNTH_API void fluid_mod_set_source1(fluid_mod_t *mod, int src, int flags);
 FLUIDSYNTH_API void fluid_mod_set_source2(fluid_mod_t *mod, int src, int flags);
 FLUIDSYNTH_API void fluid_mod_set_dest(fluid_mod_t *mod, int dst);
 FLUIDSYNTH_API void fluid_mod_set_amount(fluid_mod_t *mod, double amount);
+FLUIDSYNTH_API void fluid_mod_set_transform(fluid_mod_t *mod, int type);
 
 FLUIDSYNTH_API int fluid_mod_get_source1(const fluid_mod_t *mod);
 FLUIDSYNTH_API int fluid_mod_get_flags1(const fluid_mod_t *mod);
 FLUIDSYNTH_API int fluid_mod_get_source2(const fluid_mod_t *mod);
 FLUIDSYNTH_API int fluid_mod_get_flags2(const fluid_mod_t *mod);
 FLUIDSYNTH_API int fluid_mod_get_dest(const fluid_mod_t *mod);
 FLUIDSYNTH_API double fluid_mod_get_amount(const fluid_mod_t *mod);
+FLUIDSYNTH_API int fluid_mod_get_transform(fluid_mod_t *mod);
 
 FLUIDSYNTH_API int fluid_mod_test_identity(const fluid_mod_t *mod1, const fluid_mod_t *mod2);
 FLUIDSYNTH_API int fluid_mod_has_source(const fluid_mod_t *mod, int cc, int ctrl);

src/sfloader/fluid_defsfont.c

@@ -1639,7 +1639,7 @@ fluid_zone_mod_import_sfont(char *zone_name, fluid_mod_t **mod, SFZone *sfzone)
         /* Note: When secondary source input (src2) is set to General Controller 'No Controller',
            output will be forced to +1.0 at synthesis time (see fluid_mod_get_value()).
            That means that this source will behave unipolar only. We need to force the
-           unipolar flag to ensure to ensure a correct evaluation of the minimum
+           unipolar flag to ensure a correct evaluation of the minimum
            value later (see fluid_voice_get_lower_boundary_for_attenuation()).
         */
         if(((mod_dest->flags2 & FLUID_MOD_CC) == FLUID_MOD_GC) && 
@@ -1648,13 +1648,19 @@ fluid_zone_mod_import_sfont(char *zone_name, fluid_mod_t **mod, SFZone *sfzone)
             mod_dest->flags2 &= ~FLUID_MOD_BIPOLAR;
         }
 
-        /* *** Transform *** */
-        /* SF2.01 only uses the 'linear' transform (0).
-         * Deactivate the modulator by setting the amount to 0 in any other case.
+        /**
+         * *** Transform Type ***
+         * Only 2 types of transform are defined in the sf2 specification.
          */
-        if(mod_src->trans != 0)
+        if(mod_src->trans != FLUID_MOD_TRANSFORM_LINEAR && mod_src->trans != FLUID_MOD_TRANSFORM_ABS)
         {
+            /* disable the modulator as the transform is invalid */
             mod_dest->amount = 0;
+            mod_dest->trans = FLUID_MOD_TRANSFORM_LINEAR;
+        }
+        else
+        {
+            mod_dest->trans = mod_src->trans;
         }
 
         /* Store the new modulator in the zone The order of modulators

src/synth/fluid_mod.c

@@ -39,6 +39,7 @@ fluid_mod_clone(fluid_mod_t *mod, const fluid_mod_t *src)
     mod->src2 = src->src2;
     mod->flags2 = src->flags2;
     mod->amount = src->amount;
+    mod->trans = src->trans;
 }
 
 /**
@@ -97,6 +98,24 @@ fluid_mod_set_amount(fluid_mod_t *mod, double amount)
     mod->amount = (double) amount;
 }
 
+/**
+ * Set the transform type of a modulator.
+ *
+ * @param mod The modulator instance
+ * @param type Transform type, see #fluid_mod_transforms
+ */
+void
+fluid_mod_set_transform(fluid_mod_t *mod, int type)
+{
+    unsigned char flag = (unsigned char) type;
+    if(flag != FLUID_MOD_TRANSFORM_LINEAR && flag != FLUID_MOD_TRANSFORM_ABS)
+    {
+        FLUID_LOG(FLUID_ERR, "fluid_mod_set_transform() called with invalid transform type %d", type);
+        return;
+    }
+    mod->trans = flag;
+}
+
 /**
  * Get the primary source value from a modulator.
  *
@@ -169,6 +188,18 @@ fluid_mod_get_amount(const fluid_mod_t *mod)
     return (double) mod->amount;
 }
 
+/**
+ * Get the transform type of a modulator.
+ *
+ * @param mod The modulator instance
+ * @param type Transform type, see #fluid_mod_transforms
+ */
+int
+fluid_mod_get_transform(fluid_mod_t *mod)
+{
+    return (int) mod->trans;
+}
+
 /*
  * retrieves the initial value from the given source of the modulator
  */
@@ -382,6 +413,7 @@ fluid_mod_get_value(fluid_mod_t *mod, fluid_voice_t *voice)
     extern fluid_mod_t default_vel2filter_mod;
 
     fluid_real_t v1 = 0.0, v2 = 1.0;
+    fluid_real_t final_value;
     /* The wording of the default modulators refers to a range of 127/128.
      * And the table in section 9.5.3 suggests, that this mapping should be applied
      * to all unipolar and bipolar mappings respectively.
@@ -470,8 +502,15 @@ fluid_mod_get_value(fluid_mod_t *mod, fluid_voice_t *voice)
         v2 = 1.0f;
     }
 
-    /* it's as simple as that: */
-    return (fluid_real_t) mod->amount * v1 * v2;
+    /* it indeed is as simple as that: */
+    final_value = (fluid_real_t) mod->amount * v1 * v2;
+
+    /* check for absolute value transform */
+    if(mod->trans == FLUID_MOD_TRANSFORM_ABS)
+    {
+        final_value = FLUID_FABS(final_value);
+    }
+    return final_value;
 }
 
 /**
@@ -489,7 +528,8 @@ new_fluid_mod(void)
         FLUID_LOG(FLUID_ERR, "Out of memory");
         return NULL;
     }
-
+    // for the sake of backward compatibility
+    mod->trans = FLUID_MOD_TRANSFORM_LINEAR;
     return mod;
 }
 

src/synth/fluid_mod.h

@@ -34,6 +34,7 @@ struct _fluid_mod_t
     unsigned char flags1;         /**< Source controller 1 flags */
     unsigned char src2;           /**< Source controller 2 */
     unsigned char flags2;         /**< Source controller 2 flags */
+    unsigned char trans;          /**< Output transform flag */
     double amount;                /**< Multiplier amount */
     /* The 'next' field allows to link modulators into a list.  It is
      * not used in fluid_voice.c, there each voice allocates memory for a