int mixer_sh_start()
{
/* reset all channels to their defaults */
for (int i = 0; i < mixer_channel.Length; i++)
{
mixer_channel[i] = new mixer_channel_data();
mixer_channel[i].mixing_level = 0xff;
mixer_channel[i].default_mixing_level = 0xff;
mixer_channel[i].config_mixing_level = config_mixing_level[i];
mixer_channel[i].config_default_mixing_level = config_default_mixing_level[i];
}
/* determine if we're playing in stereo or not */
first_free_channel = 0;
is_stereo = ((Machine.drv.sound_attributes & SOUND_SUPPORTS_STEREO) != 0);
/* clear the accumulators */
accum_base = 0;
for (int i = 0; i < ACCUMULATOR_SAMPLES; i++)
{
left_accum[i] = 0;
right_accum[i] = 0;
}
samples_this_frame = (uint)osd_start_audio_stream(is_stereo);
mixer_sound_enabled = true;
return 0;
}
static void mix_sample_16(mixer_channel_data channel, int samples_to_generate)
{
uint step_size, input_frac, output_pos;
_ShortPtr source;
int source_end;
int mixing_volume;
/* compute the overall mixing volume */
if (mixer_sound_enabled)
mixing_volume = ((channel.volume * channel.mixing_level * 256) << channel.gain) / (100 * 100);
else
mixing_volume = 0;
/* get the initial state */
step_size = channel.step_size;
source = new _ShortPtr(channel.data_current);
source_end = channel.data_end;
input_frac = channel.input_frac;
output_pos = (accum_base + channel.samples_available) & ACCUMULATOR_MASK;
/* an outer loop to handle looping samples */
while (samples_to_generate > 0)
{
/* if we're mono or left panning, just mix to the left channel */
if (!is_stereo || channel.pan == MIXER_PAN_LEFT)
{
while (source.offset < source_end && samples_to_generate > 0)
{
left_accum[output_pos] += (source.read16(0) * mixing_volume) >> 8;
input_frac += step_size;
source.offset += (int)(input_frac >> FRACTION_BITS) * 2;
input_frac &= FRACTION_MASK;
output_pos = (output_pos + 1) & ACCUMULATOR_MASK;
samples_to_generate--;
}
}
/* if we're right panning, just mix to the right channel */
else if (channel.pan == MIXER_PAN_RIGHT)
{
while (source.offset < source_end && samples_to_generate > 0)
{
right_accum[output_pos] += (source.read16(0) * mixing_volume) >> 8;
input_frac += step_size;
source.offset += (int)(input_frac >> FRACTION_BITS) * 2;
input_frac &= FRACTION_MASK;
output_pos = (output_pos + 1) & ACCUMULATOR_MASK;
samples_to_generate--;
}
}
/* if we're stereo center, mix to both channels */
else
{
while (source.offset < source_end && samples_to_generate > 0)
{
int mixing_value = (source.read16(0) * mixing_volume) >> 8;
left_accum[output_pos] += mixing_value;
right_accum[output_pos] += mixing_value;
input_frac += step_size;
source.offset += (int)(input_frac >> FRACTION_BITS) * 2;
input_frac &= FRACTION_MASK;
output_pos = (output_pos + 1) & ACCUMULATOR_MASK;
samples_to_generate--;
}
}
/* handle the end case */
if (source.offset >= source_end)
{
/* if we're done, stop playing */
if (!channel.is_looping)
{
channel.is_playing = false;
break;
}
/* if we're looping, wrap to the beginning */
else
source.offset-=source_end;// source.offset -= (INT16*)source_end - (INT16*)channel.data_start;
}
}
/* update the final positions */
channel.input_frac = input_frac;
channel.data_current = source.offset;
}
static void mixer_update_channel(mixer_channel_data channel, int total_sample_count)
{
int samples_to_generate = (int)(total_sample_count - channel.samples_available);
/* don't do anything for streaming channels */
if (channel.is_stream)
return;
/* if we're all caught up, just return */
if (samples_to_generate <= 0)
return;
/* if we're playing, mix in the data */
if (channel.is_playing)
{
if (channel.is_16bit)
mix_sample_16(channel, samples_to_generate);
else
mix_sample_8(channel, samples_to_generate);
}
/* just eat the rest */
channel.samples_available += (uint)samples_to_generate;
}