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-rw-r--r--src/mixer.cpp140
1 files changed, 140 insertions, 0 deletions
diff --git a/src/mixer.cpp b/src/mixer.cpp
new file mode 100644
index 000000000..5b97afbf9
--- /dev/null
+++ b/src/mixer.cpp
@@ -0,0 +1,140 @@
+/* $Id$ */
+
+#include "stdafx.h"
+#include "openttd.h"
+#include "mixer.h"
+
+struct MixerChannel {
+ bool active;
+
+ // pointer to allocated buffer memory
+ int8 *memory;
+
+ // current position in memory
+ uint32 pos;
+ uint32 frac_pos;
+ uint32 frac_speed;
+ uint32 samples_left;
+
+ // Mixing volume
+ uint volume_left;
+ uint volume_right;
+
+ uint flags;
+};
+
+static MixerChannel _channels[8];
+static uint32 _play_rate;
+
+
+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;
+
+ if (samples > sc->samples_left) samples = sc->samples_left;
+ sc->samples_left -= samples;
+ assert(samples > 0);
+
+ b = sc->memory + sc->pos;
+ frac_pos = sc->frac_pos;
+ frac_speed = sc->frac_speed;
+ volume_left = sc->volume_left;
+ volume_right = sc->volume_right;
+
+ if (frac_speed == 0x10000) {
+ // Special case when frac_speed is 0x10000
+ do {
+ buffer[0] += *b * volume_left >> 8;
+ buffer[1] += *b * volume_right >> 8;
+ b++;
+ buffer += 2;
+ } while (--samples > 0);
+ } else {
+ do {
+ buffer[0] += *b * volume_left >> 8;
+ buffer[1] += *b * volume_right >> 8;
+ buffer += 2;
+ frac_pos += frac_speed;
+ b += frac_pos >> 16;
+ frac_pos &= 0xffff;
+ } while (--samples > 0);
+ }
+
+ sc->frac_pos = frac_pos;
+ sc->pos = b - sc->memory;
+}
+
+static void MxCloseChannel(MixerChannel *mc)
+{
+ if (mc->flags & MX_AUTOFREE) free(mc->memory);
+ mc->active = false;
+ mc->memory = NULL;
+}
+
+void MxMixSamples(void *buffer, uint samples)
+{
+ MixerChannel *mc;
+
+ // Clear the buffer
+ memset(buffer, 0, sizeof(int16) * 2 * samples);
+
+ // Mix each channel
+ for (mc = _channels; mc != endof(_channels); mc++) {
+ if (mc->active) {
+ mix_int8_to_int16(mc, buffer, samples);
+ if (mc->samples_left == 0) MxCloseChannel(mc);
+ }
+ }
+}
+
+MixerChannel *MxAllocateChannel(void)
+{
+ MixerChannel *mc;
+ for (mc = _channels; mc != endof(_channels); mc++)
+ if (mc->memory == NULL) {
+ mc->active = false;
+ return mc;
+ }
+ return NULL;
+}
+
+void MxSetChannelRawSrc(MixerChannel *mc, int8 *mem, uint size, uint rate, uint flags)
+{
+ mc->memory = mem;
+ mc->flags = flags;
+ mc->frac_pos = 0;
+ mc->pos = 0;
+
+ mc->frac_speed = (rate << 16) / _play_rate;
+
+ // adjust the magnitude to prevent overflow
+ while (size & 0xFFFF0000) {
+ size >>= 1;
+ rate = (rate >> 1) + 1;
+ }
+
+ mc->samples_left = size * _play_rate / rate;
+}
+
+void MxSetChannelVolume(MixerChannel *mc, uint left, uint right)
+{
+ mc->volume_left = left;
+ mc->volume_right = right;
+}
+
+
+void MxActivateChannel(MixerChannel* mc)
+{
+ mc->active = true;
+}
+
+
+bool MxInitialize(uint rate)
+{
+ _play_rate = rate;
+ return true;
+}