test/refactor: arpgeggiator::midi_cv::Gate values roundtrip (Synthstr…

…omAudible#2087)

- Pull out the guts for testing: the current value math is identical to
  standard, so share the machinery, but the final value computation
  produces numbers that are slightly smaller near the max values,
  and needs to remain distinct. They use-provided values roundtrip
  despite the asymmetry.

- Speculate on the reason things are the way they are.

src/deluge/gui/menu_item/arpeggiator/midi_cv/gate.h

@@ -16,6 +16,7 @@
  */
 #pragma once
 #include "gui/menu_item/integer.h"
+#include "gui/menu_item/value_scaling.h"
 #include "gui/ui/sound_editor.h"
 #include "model/clip/instrument_clip.h"
 #include "model/song/song.h"
@@ -25,12 +26,10 @@ class Gate final : public Integer {
 public:
  using Integer::Integer;
  void readCurrentValue() override {
- auto* current_clip = getCurrentInstrumentClip();
- int64_t arp_gate = (int64_t)current_clip->arpeggiatorGate + 2147483648;
- this->setValue((arp_gate * kMaxMenuValue + 2147483648) >> 32);
+ this->setValue(computeCurrentValueForArpMidiCvGate(getCurrentInstrumentClip()->arpeggiatorGate));
  }
  void writeCurrentValue() override {
- getCurrentInstrumentClip()->arpeggiatorGate = (uint32_t)this->getValue() * 85899345 - 2147483648;
+ getCurrentInstrumentClip()->arpeggiatorGate = computeFinalValueForArpMidiCvGate(this->getValue());
  }
  [[nodiscard]] int32_t getMaxValue() const override { return kMaxMenuValue; }
  bool isRelevant(ModControllableAudio* modControllable, int32_t whichThing) override {

src/deluge/gui/menu_item/value_scaling.cpp

@@ -15,6 +15,10 @@ int32_t computeCurrentValueForPan(int32_t value) {
  return ((int64_t)value * (kMaxMenuRelativeValue * 2) + 2147483648) >> 32;
 }
 
+int32_t computeCurrentValueForArpMidiCvGate(int32_t value) {
+ return computeCurrentValueForStandardMenuItem(value);
+}
+
 int32_t computeFinalValueForStandardMenuItem(int32_t value) {
  if (value == kMaxMenuValue) {
  return 2147483647;
@@ -64,3 +68,7 @@ int32_t computeFinalValueForPan(int32_t value) {
  return ((int32_t)value * (2147483648 / (kMaxMenuRelativeValue * 2)) * 2);
  }
 }
+
+int32_t computeFinalValueForArpMidiCvGate(int32_t value) {
+ return (uint32_t)value * 85899345 - 2147483648;
+}

src/deluge/gui/menu_item/value_scaling.h

@@ -26,6 +26,7 @@
 ///
 /// Done:
 /// - audio_compressor::CompParam
+/// - arpeggiator::midi_cv::Gate
 /// - osc::PulseWidth
 /// - patched_param::Integer
 /// - patched_param::Pan
@@ -68,3 +69,18 @@ int32_t computeCurrentValueForPan(int32_t value);
 /** Scales -25 to 25 range to INT32_MIN-INT32_MAX for storage and use.
  */
 int32_t computeFinalValueForPan(int32_t value);
+
+/** Scales INT32_MIN-INT32_MAX range to 0-50 for display.
+ *
+ * This roundtrips with the final value math despite not
+ * being it's proper inverse.
+ */
+int32_t computeCurrentValueForArpMidiCvGate(int32_t value);
+
+/** Scales 0-50 range to INT32_MIN-(INT32_MAX-45) for storage and use.
+ *
+ * This is presumably to have the gate go down even at 50: the values
+ * produced create a 2.5ms gate down period between 16th arp notes at Gate=50,
+ * which exactly matches the gate down period between regular 16h notes.
+ */
+int32_t computeFinalValueForArpMidiCvGate(int32_t value);

tests/unit/value_scaling_tests.cpp

@@ -38,3 +38,20 @@ TEST(ValueScalingTest, panValueScaling) {
  CHECK_EQUAL(0, computeFinalValueForPan(0));
  CHECK_EQUAL(INT32_MAX, computeFinalValueForPan(25));
 }
+
+TEST(ValueScalingTest, arpMidiCvGateValueScaling) {
+ for (int i = kMinMenuValue; i <= kMaxMenuValue; i++) {
+ int32_t finalValue = computeFinalValueForArpMidiCvGate(i);
+ int32_t currentValue = computeCurrentValueForArpMidiCvGate(finalValue);
+ CHECK_EQUAL(i, currentValue);
+ }
+ CHECK_EQUAL(INT32_MIN, computeFinalValueForArpMidiCvGate(0));
+ CHECK_EQUAL(-23, computeFinalValueForArpMidiCvGate(25));
+ // As seen here, we diverge _slightly_ from the standard
+ // menu item scaling when computing final values, despite roundtripping
+ // and using the identical current value computation.
+ //
+ // See computeFinalValueForArpMidiCvGate()'s comment for possible
+ // motivation.
+ CHECK_EQUAL(INT32_MAX-45, computeFinalValueForArpMidiCvGate(50));
+}