fix(simu): wire Companion volume gain into audio output

OpenTxSimulator::setVolumeGain wrote to a field that was never
read, so the Companion "Simulator volume gain" preference (0.5-3.0x)
had no effect on simulator audio.

Add simuSetVolumeGain() and apply the gain in simuQueueAudio with
saturation on the int16 samples, so 0.5-1.0x attenuates, 1.0x is
unity, and 1.0-3.0x amplifies with clipping at INT16_MIN/MAX
(SDL_MixAudioFormat cannot amplify above unity).

Author: raphaelcoeffic

radio/src/targets/simu/opentxsimulator.cpp

@@ -307,8 +307,7 @@ void OpenTxSimulator::setSdPath(const QString & sdPath, const QString & settings
 
 void OpenTxSimulator::setVolumeGain(const int value)
 {
-  QMutexLocker lckr(&m_mtxSettings);
-  volumeGain = value;
+  simuSetVolumeGain(value);
 }
 
 void OpenTxSimulator::setRadioData(const QByteArray & data)

radio/src/targets/simu/opentxsimulator.h

@@ -116,7 +116,6 @@ class DLLEXPORT OpenTxSimulator : public SimulatorInterface
     QMutex m_mtxRadioData;
     QMutex m_mtxSettings;
     QMutex m_mtxTbDevices;
-    int volumeGain;
     bool m_resetOutputsData;
     bool m_stopRequested;
 

radio/src/targets/simu/simuaudio.cpp

@@ -29,13 +29,37 @@
 
 static SDL_AudioDeviceID _sdl_audio_device = 0;
 
+// Companion-side volume gain, stored as user-facing gain (0.5..3.0x) * 10.
+// Default 10 = unity.
+static int _volume_gain = 10;
+
+void simuSetVolumeGain(int value)
+{
+  _volume_gain = value;
+}
+
 void simuQueueAudio(const uint8_t* data, uint32_t len)
 {
 #if !defined(SOFTWARE_VOLUME)
   int volume = (simuAudioGetVolume() * SDL_MIX_MAXVOLUME ) / VOLUME_LEVEL_MAX;
   SDL_MixAudioFormat((uint8_t*)data, data, AUDIO_FMT, len, volume);
 #endif
 
+  int gain = _volume_gain;
+  if (gain != 10) {
+    // SDL_MixAudioFormat cannot amplify above unity, so apply the
+    // Companion gain manually with saturation to support the full
+    // 0.5..3.0x UI range.
+    auto* samples = (int16_t*)data;
+    uint32_t n = len / sizeof(int16_t);
+    for (uint32_t i = 0; i < n; ++i) {
+      int32_t s = ((int32_t)samples[i] * gain) / 10;
+      if (s > INT16_MAX) s = INT16_MAX;
+      else if (s < INT16_MIN) s = INT16_MIN;
+      samples[i] = (int16_t)s;
+    }
+  }
+
   SDL_QueueAudio(_sdl_audio_device, data, len);
 }
 

radio/src/targets/simu/simuaudio.h

@@ -27,3 +27,4 @@ bool simuAudioInit();
 void simuAudioDeInit();
 void simuQueueAudio(const uint8_t* data, uint32_t len);
 int simuAudioGetVolume();
+void simuSetVolumeGain(int value);