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(svn r13695) -Fix [FS#2120]: in some cases the (sound) mixer could overflow causing artefacts in the sound.

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rubidium 2008-07-12 22:30:10 +00:00
parent e74743227b
commit 53436082a2
1 changed files with 17 additions and 8 deletions
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25
src/mixer.cpp
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@ -5,6 +5,7 @@
#include "stdafx.h" #include "stdafx.h"
#include "openttd.h" #include "openttd.h"
#include "mixer.h" #include "mixer.h"
#include "core/math_func.hpp"
struct MixerChannel { struct MixerChannel {
bool active; bool active;
@ -19,8 +20,8 @@ struct MixerChannel {
uint32 samples_left; uint32 samples_left;
/* Mixing volume */ /* Mixing volume */
uint volume_left; int volume_left;
uint volume_right; int volume_right;
uint flags; uint flags;
}; };
@ -28,14 +29,22 @@ struct MixerChannel {
static MixerChannel _channels[8]; static MixerChannel _channels[8];
static uint32 _play_rate; 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) static void mix_int8_to_int16(MixerChannel *sc, int16 *buffer, uint samples)
{ {
int8 *b; int8 *b;
uint32 frac_pos; uint32 frac_pos;
uint32 frac_speed; uint32 frac_speed;
uint volume_left; int volume_left;
uint volume_right; int volume_right;
if (samples > sc->samples_left) samples = sc->samples_left; if (samples > sc->samples_left) samples = sc->samples_left;
sc->samples_left -= samples; sc->samples_left -= samples;
@ -50,15 +59,15 @@ static void mix_int8_to_int16(MixerChannel *sc, int16 *buffer, uint samples)
if (frac_speed == 0x10000) { if (frac_speed == 0x10000) {
/* Special case when frac_speed is 0x10000 */ /* Special case when frac_speed is 0x10000 */
do { do {
buffer[0] += *b * volume_left >> 8; buffer[0] = Clamp(buffer[0] + (*b * volume_left >> 8), -MAX_VOLUME, MAX_VOLUME);
buffer[1] += *b * volume_right >> 8; buffer[0] = Clamp(buffer[1] + (*b * volume_right >> 8), -MAX_VOLUME, MAX_VOLUME);
b++; b++;
buffer += 2; buffer += 2;
} while (--samples > 0); } while (--samples > 0);
} else { } else {
do { do {
buffer[0] += *b * volume_left >> 8; buffer[0] = Clamp(buffer[0] + (*b * volume_left >> 8), -MAX_VOLUME, MAX_VOLUME);
buffer[1] += *b * volume_right >> 8; buffer[0] = Clamp(buffer[1] + (*b * volume_right >> 8), -MAX_VOLUME, MAX_VOLUME);
buffer += 2; buffer += 2;
frac_pos += frac_speed; frac_pos += frac_speed;
b += frac_pos >> 16; b += frac_pos >> 16;