(svn r13695) -Fix [FS#2120]: in some cases the (sound) mixer could overflow causing artefacts in the sound.
--- a/src/mixer.cpp Sat Jul 12 22:28:34 2008 +0000
+++ b/src/mixer.cpp Sat Jul 12 22:30:10 2008 +0000
@@ -5,6 +5,7 @@
#include "stdafx.h"
#include "openttd.h"
#include "mixer.h"
+#include "core/math_func.hpp"
struct MixerChannel {
bool active;
@@ -19,8 +20,8 @@
uint32 samples_left;
/* Mixing volume */
- uint volume_left;
- uint volume_right;
+ int volume_left;
+ int volume_right;
uint flags;
};
@@ -28,14 +29,22 @@
static MixerChannel _channels[8];
static uint32 _play_rate;
+/**
+ * The theoretical maximum volume for a single sound sample. Multiple sound
+ * samples should not exceed this limit as it will sound too loud. It also
+ * stops overflowing when too many sounds are played at the same time, which
+ * causes an even worse sound quality.
+ */
+static const int MAX_VOLUME = 128 * 128;
+
static void mix_int8_to_int16(MixerChannel *sc, int16 *buffer, uint samples)
{
int8 *b;
uint32 frac_pos;
uint32 frac_speed;
- uint volume_left;
- uint volume_right;
+ int volume_left;
+ int volume_right;
if (samples > sc->samples_left) samples = sc->samples_left;
sc->samples_left -= samples;
@@ -50,15 +59,15 @@
if (frac_speed == 0x10000) {
/* Special case when frac_speed is 0x10000 */
do {
- buffer[0] += *b * volume_left >> 8;
- buffer[1] += *b * volume_right >> 8;
+ buffer[0] = Clamp(buffer[0] + (*b * volume_left >> 8), -MAX_VOLUME, MAX_VOLUME);
+ buffer[0] = Clamp(buffer[1] + (*b * volume_right >> 8), -MAX_VOLUME, MAX_VOLUME);
b++;
buffer += 2;
} while (--samples > 0);
} else {
do {
- buffer[0] += *b * volume_left >> 8;
- buffer[1] += *b * volume_right >> 8;
+ buffer[0] = Clamp(buffer[0] + (*b * volume_left >> 8), -MAX_VOLUME, MAX_VOLUME);
+ buffer[0] = Clamp(buffer[1] + (*b * volume_right >> 8), -MAX_VOLUME, MAX_VOLUME);
buffer += 2;
frac_pos += frac_speed;
b += frac_pos >> 16;