Ticket #8317: panvolume.diff

scummvm/sound/mixer.cpp

@@ -496 +496 @@
         } else {
                 assert(_converter);
 
-                // The pan value ranges from -127 to +127. That's 255 different values.
-                // From the channel pan/volume and the global volume, we compute the
-                // effective volume for the left and right channel.
-                // Note the slightly odd divisor: the 255 reflects the fact that
-                // the maximal value for _volume is 255, while the 254 is there
-                // because the maximal left/right pan value is 2*127 = 254.
+                // From the channel pan/volume and the global volume, we
+                // compute the effective volume for the left and right channel.
+                // Note the slightly odd divisor: the 255 reflects the fact
+                // that the maximal value for _volume is 255, while the 127 is
+                // there because the pan value ranges from -127 to 127.
                 // The value getVolume() returns is in the range 0 - 256.
                 // Hence, the vol_l/vol_r values will be in that range, too
                 
                 int vol = getVolume() * _volume;
-                st_volume_t vol_l = (127 - _pan) * vol / (255 * 254);
-                st_volume_t vol_r = (127 + _pan) * vol / (255 * 254);
+                st_volume_t vol_l, vol_r;
+
+                if (_pan == 0) {
+                        vol_l = vol / 255;
+                        vol_r = vol / 255;
+                } else if (_pan < 0) {
+                        vol_l = vol / 255;
+                        vol_r = ((127 + _pan) * vol) / (255 * 127);
+                } else {
+                        vol_l = ((127 - _pan) * vol) / (255 * 127);
+                        vol_r = vol / 255;
+                }
 
                 _converter->flow(*_input, data, len, vol_l, vol_r);
         }