mixer.c
author pasky
Sun, 27 Mar 2005 15:13:51 +0000
changeset 1583 7617a49e78e8
parent 1498 508395d0639a
child 1891 862800791170
permissions -rw-r--r--
(svn r2087) Show also the modified filenames along each change in svn log. Prevents enraging Darkvater, and we show the commit messages along changed files everywhere else too (on IRC and in mail).
#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->active = false;
	mc->memory = NULL;
}

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 MxActivateChannel(MixerChannel* mc)
{
	mc->active = true;
}


bool MxInitialize(uint rate)
{
	static Mixer mx;
	_mixer = &mx;
	mx.play_rate = rate;
	return true;
}