1 files changed, 154 insertions, 0 deletions
diff --git a/mixer.c b/mixer.c
new file mode 100644
index 000000000..1a113dbed
--- /dev/null
+++ b/mixer.c
@@ -0,0 +1,154 @@
+#include "stdafx.h"
+#include "ttd.h"
+#include "mixer.h"
+
+struct MixerChannel {
+	// Mixer
+	Mixer *mx;
+	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;
+};
+
+struct Mixer {
+	uint32 play_rate;
+	MixerChannel channels[8];
+};
+
+
+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->memory = NULL;
+	mc->active = false;
+}
+
+void MxMixSamples(Mixer *mx, void *buffer, uint samples)
+{
+	MixerChannel *mc;
+
+	// Clear the buffer
+	memset(buffer, 0, sizeof(int16) * 2 * samples);
+
+	// Mix each channel
+	for (mc = mx->channels; mc != endof(mx->channels); mc++) {
+		if (mc->active) {
+			mix_int8_to_int16(mc, buffer, samples);
+			if (mc->samples_left == 0) MxCloseChannel(mc);
+		}
+	}
+
+	#if 0
+	{
+		static FILE *out = NULL;
+		if (out == NULL)
+			out = fopen("d:\\dump.raw", "wb");
+		fwrite(buffer, samples * 4, 1, out);
+	}
+	#endif
+}
+
+MixerChannel *MxAllocateChannel(Mixer *mx)
+{
+	MixerChannel *mc;
+	for (mc = mx->channels; mc != endof(mx->channels); mc++)
+		if (mc->memory == NULL) {
+			mc->active = false;
+			mc->mx = mx;
+			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) / mc->mx->play_rate;
+
+	// adjust the magnitude to prevent overflow
+	while (size & 0xFFFF0000) {
+		size >>= 1;
+		rate = (rate >> 1) + 1;
+	}
+
+	mc->samples_left = size * mc->mx->play_rate / rate;
+}
+
+void MxSetChannelVolume(MixerChannel *mc, uint left, uint right)
+{
+	mc->volume_left = left;
+	mc->volume_right = right;
+}
+
+
+void MxActivate(MixerChannel* mc)
+{
+	mc->active = true;
+}
+
+
+bool MxInitialize(uint rate)
+{
+	static Mixer mx;
+	_mixer = &mx;
+	mx.play_rate = rate;
+	return true;
+}