synthio: lfo: bugfixes & improvements

LFO waveforms are now linearly interpolated by default, but a new
property (interpolated=False) can disable this.

The 'once' logic was improved

shared-bindings/synthio/LFO.c

@@ -64,7 +64,8 @@
 //|         scale: BlockInput = 1.0,
 //|         offset: BlockInput = 0,
 //|         phase_offset: BlockInput = 0,
-//|         once=False
+//|         once=False,
+//|         interpolate=True
 //|     ):
 //|         pass
 static const mp_arg_t lfo_properties[] = {
@@ -74,6 +75,7 @@ static const mp_arg_t lfo_properties[] = {
     { MP_QSTR_offset, MP_ARG_OBJ | MP_ARG_KW_ONLY, {.u_obj = MP_ROM_INT(0) } },
     { MP_QSTR_phase_offset, MP_ARG_OBJ | MP_ARG_KW_ONLY, {.u_obj = MP_ROM_INT(0) } },
     { MP_QSTR_once, MP_ARG_OBJ | MP_ARG_KW_ONLY, {.u_obj = MP_ROM_INT(0) } },
+    { MP_QSTR_interpolate, MP_ARG_OBJ | MP_ARG_KW_ONLY, {.u_obj = MP_ROM_INT(1) } },
 };
 
 STATIC mp_obj_t synthio_lfo_make_new(const mp_obj_type_t *type_in, size_t n_args, size_t n_kw, const mp_obj_t *all_args) {
@@ -201,6 +203,26 @@ MP_PROPERTY_GETSET(synthio_lfo_once_obj,
     (mp_obj_t)&synthio_lfo_set_once_obj);
 
 
+//|
+//|     interpolate: bool
+//|     """True if the waveform should perform linear interpolation between values"""
+STATIC mp_obj_t synthio_lfo_get_interpolate(mp_obj_t self_in) {
+    synthio_lfo_obj_t *self = MP_OBJ_TO_PTR(self_in);
+    return mp_obj_new_bool(common_hal_synthio_lfo_get_interpolate(self));
+}
+MP_DEFINE_CONST_FUN_OBJ_1(synthio_lfo_get_interpolate_obj, synthio_lfo_get_interpolate);
+
+STATIC mp_obj_t synthio_lfo_set_interpolate(mp_obj_t self_in, mp_obj_t arg) {
+    synthio_lfo_obj_t *self = MP_OBJ_TO_PTR(self_in);
+    common_hal_synthio_lfo_set_interpolate(self, mp_obj_is_true(arg));
+    return mp_const_none;
+}
+MP_DEFINE_CONST_FUN_OBJ_2(synthio_lfo_set_interpolate_obj, synthio_lfo_set_interpolate);
+MP_PROPERTY_GETSET(synthio_lfo_interpolate_obj,
+    (mp_obj_t)&synthio_lfo_get_interpolate_obj,
+    (mp_obj_t)&synthio_lfo_set_interpolate_obj);
+
+
 //|
 //|     phase: float
 //|     """The phase of the oscillator, in the range 0 to 1 (read-only)"""
@@ -250,6 +272,7 @@ STATIC const mp_rom_map_elem_t synthio_lfo_locals_dict_table[] = {
     { MP_ROM_QSTR(MP_QSTR_offset), MP_ROM_PTR(&synthio_lfo_offset_obj) },
     { MP_ROM_QSTR(MP_QSTR_phase_offset), MP_ROM_PTR(&synthio_lfo_phase_offset_obj) },
     { MP_ROM_QSTR(MP_QSTR_once), MP_ROM_PTR(&synthio_lfo_once_obj) },
+    { MP_ROM_QSTR(MP_QSTR_interpolate), MP_ROM_PTR(&synthio_lfo_interpolate_obj) },
     { MP_ROM_QSTR(MP_QSTR_value), MP_ROM_PTR(&synthio_lfo_value_obj) },
     { MP_ROM_QSTR(MP_QSTR_phase), MP_ROM_PTR(&synthio_lfo_phase_obj) },
     { MP_ROM_QSTR(MP_QSTR_retrigger), MP_ROM_PTR(&synthio_lfo_retrigger_obj) },

shared-bindings/synthio/LFO.h

@@ -49,6 +49,9 @@ void common_hal_synthio_lfo_set_offset_obj(synthio_lfo_obj_t *self, mp_obj_t arg
 bool common_hal_synthio_lfo_get_once(synthio_lfo_obj_t *self);
 void common_hal_synthio_lfo_set_once(synthio_lfo_obj_t *self, bool arg);
 
+bool common_hal_synthio_lfo_get_interpolate(synthio_lfo_obj_t *self);
+void common_hal_synthio_lfo_set_interpolate(synthio_lfo_obj_t *self, bool arg);
+
 mp_float_t common_hal_synthio_lfo_get_value(synthio_lfo_obj_t *self);
 
 mp_float_t common_hal_synthio_lfo_get_phase(synthio_lfo_obj_t *self);

shared-module/synthio/LFO.c

@@ -31,6 +31,8 @@
 #define ONE (MICROPY_FLOAT_CONST(1.))
 #define ZERO (MICROPY_FLOAT_CONST(0.))
 
+#define ALMOST_ONE (MICROPY_FLOAT_CONST(32767.) / 32768)
+
 mp_float_t common_hal_synthio_lfo_tick(mp_obj_t self_in) {
     synthio_lfo_obj_t *lfo = MP_OBJ_TO_PTR(self_in);
 
@@ -41,8 +43,8 @@ mp_float_t common_hal_synthio_lfo_tick(mp_obj_t self_in) {
 
     if (lfo->once) {
         if (rate > 0) {
-            if (accum >= ONE) {
-                accum = ONE;
+            if (accum > ALMOST_ONE) {
+                accum = ALMOST_ONE;
             }
         } else if (rate < 0 && accum < ZERO) {
             accum = ZERO;
@@ -50,17 +52,32 @@ mp_float_t common_hal_synthio_lfo_tick(mp_obj_t self_in) {
     } else {
         accum = accum - MICROPY_FLOAT_C_FUN(floor)(accum);
     }
+    lfo->accum = accum - phase_offset;
 
     int len = lfo->waveform_bufinfo.len;
-    size_t idx = (int)(accum * len); // rounds down towards zero
+
+    mp_float_t scaled_accum = accum * (len - lfo->once);
+    size_t idx = (size_t)MICROPY_FLOAT_C_FUN(floor)(scaled_accum);
     assert(idx < lfo->waveform_bufinfo.len);
 
+    int16_t *waveform = lfo->waveform_bufinfo.buf;
+    mp_float_t value = waveform[idx];
+
+    if (lfo->interpolate) {
+
+        mp_float_t frac = scaled_accum - idx;
+
+        size_t idxp1 = idx + 1;
+        if (idxp1 == lfo->waveform_bufinfo.len) {
+            idxp1 = lfo->once ? idx : 0;
+        }
+        value = value * (1 - frac) + waveform[idxp1] * frac;
+    }
+
     mp_float_t scale = synthio_block_slot_get(&lfo->scale);
     mp_float_t offset = synthio_block_slot_get(&lfo->offset);
-    int16_t *waveform = lfo->waveform_bufinfo.buf;
-    mp_float_t value = MICROPY_FLOAT_C_FUN(ldexp)(waveform[idx], -15) * scale + offset;
+    value = MICROPY_FLOAT_C_FUN(ldexp)(value, -15) * scale + offset;
 
-    lfo->accum = accum - phase_offset;
     return value;
 }
 
@@ -104,6 +121,13 @@ void common_hal_synthio_lfo_set_once(synthio_lfo_obj_t *self, bool arg) {
     self->once = arg;
 }
 
+bool common_hal_synthio_lfo_get_interpolate(synthio_lfo_obj_t *self) {
+    return self->interpolate;
+}
+void common_hal_synthio_lfo_set_interpolate(synthio_lfo_obj_t *self, bool arg) {
+    self->interpolate = arg;
+}
+
 mp_float_t common_hal_synthio_lfo_get_value(synthio_lfo_obj_t *self) {
     return self->base.value;
 }

shared-module/synthio/LFO.h

@@ -30,7 +30,7 @@
 
 typedef struct synthio_lfo_obj {
     synthio_block_base_t base;
-    bool once;
+    bool once, interpolate;
 
     synthio_block_slot_t rate, scale, offset, phase_offset;
     mp_float_t accum;