xine engine: make volume control logarithmic for versions of xine < 1.2.13.

For xine versions >= 1.2.13, libxine already makes the volume logarithmic.
This relates to TDE/tdemultimedia#40.

This commit makes the behavior consistent across different xine versions
and aligned with other players like Amarok.

Signed-off-by: Michele Calgaro <michele.calgaro@yahoo.it>

kaffeine/src/player-parts/xine-part/kxinewidget.cpp

@@ -61,6 +61,8 @@
 #define TIMER_EVENT_RESIZE_PARENT       300
 
 
+bool KXineWidget::s_logarithmicVolume = false;
+
 KXineWidget::KXineWidget(TQWidget* parent, const char* name,
                          const TQString& pathToConfigFile, const TQString& pathToLogoFile,
                          const TQString& audioDriver, const TQString& videoDriver,
@@ -117,6 +119,13 @@ KXineWidget::KXineWidget(TQWidget* parent, const char* name,
 
 	setUpdatesEnabled(false);
 	setMouseTracking(true);
+
+	// Detect xine version, this is used for volume adjustment.
+	// Xine versions prior to 1.2.13 use linear volume, so the engine uses logarithmic volume.
+	// Xine versions starting from 1.2.13 use logarithmic volume, so the engine uses linear volume.
+	int xinemajor = 0, xineminor = 0, xinemaint = 0;
+	xine_get_version(&xinemajor, &xineminor, &xinemaint);
+	s_logarithmicVolume = (xinemajor * 1000000 + xineminor * 1000 + xinemaint < 1002013);
 }
 
 
@@ -2667,16 +2676,28 @@ bool KXineWidget::getAutoplayPluginURLS(const TQString& plugin, TQStringList& li
 	}
 }
 
+int KXineWidget::makeVolumeLogarithmic(int volume)
+{
+	// We're using a logarithmic function to make the volume ramp more natural.
+	return static_cast<uint>( 100 - 100.0 * std::log10( ( 100 - volume ) * 0.09 + 1.0 ) );
+}
+
 void KXineWidget::slotSetVolume(int vol)
 {
 	if (!isXineReady()) return;
+
 	if (m_softwareMixer)
 	{
+		int xine_vol = vol;
+		if (s_logarithmicVolume)
+		{
+			xine_vol = makeVolumeLogarithmic(vol);
+		}
 		//debugOut(TQString("Set software amplification level: %1").arg(vol));
 		if (m_volumeGain)
-			xine_set_param(m_xineStream, XINE_PARAM_AUDIO_AMP_LEVEL, vol*2);
+			xine_set_param(m_xineStream, XINE_PARAM_AUDIO_AMP_LEVEL, xine_vol*2);
 		else
-			xine_set_param(m_xineStream, XINE_PARAM_AUDIO_AMP_LEVEL, vol);
+			xine_set_param(m_xineStream, XINE_PARAM_AUDIO_AMP_LEVEL, xine_vol);
 	}
 	else
 	{
@@ -2696,8 +2717,8 @@ uint KXineWidget::getVolume() const
 		if (vol > 200)
 		{
 			// when amp is high > 100, xine_get_param sometimes returns incorrect amp level
-			errorOut("Amp level returned weird results, set Amp to 100");
-			vol = 100;
+			errorOut("Amp level returned weird results, set Amp to 200");
+			vol = 200;
 		}
 		if (m_volumeGain) vol = vol/2;
 	}

kaffeine/src/player-parts/xine-part/kxinewidget.h

@@ -316,6 +316,10 @@ protected:
 	void initOSD();
 	virtual void run();
 
+  static int makeVolumeLogarithmic(int volume);
+
+  static bool s_logarithmicVolume;
+
 private:
 #ifndef HAVE_XCB
 	bool x11Event(XEvent *);