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This file is part of Open Sound System.
Copyright (C) 4Front Technologies 1996-2008.
This this source file is released under GPL v2 license (no other versions). See the COPYING file included in the main directory of this source distribution for the license terms and conditions.
Mixing function for virtual devices
vmix_mixer_t *mixer = portc->mixer; vmix_engine_t *eng = &mixer->play_engine; dmap_t *dmap = audio_engines[portc->audio_dev]->dmap_out; int frame_size; int inptr, inmax; int used_channels; int i, ch, nch; int vol;
Initial setup
frame_size = sizeof (*inp); inmax = dmap->bytes_in_use / frame_size; inptr = portc->play_dma_pointer / frame_size; inp = (BUFFER_TYPE) dmap->dmabuf; used_channels = portc->channels; if (used_channels > eng->channels) used_channels = eng->channels; /* ignored_channels = portc->channels - used_channels; */
Handle mono playback by playing the mono stream twice (for left and right ch)
nch=used_channels; if (nch<2)nch=2;
Do the mixing
for (ch = 0; ch < nch; ch++)
{
int ip = inptr + (ch%used_channels);
int vu = portc->vu[ch % 2];
int *chbuf = eng->chbufs[ch+portc->play_choffs];
i = portc->volume[ch%2];
vol = vmix_db_table[i / 5];
vu = vu * 65536;
for (i = 0; i < nsamples; i++)
{
int tmp;
Convert the sample to right endianess.
tmp = INT_OUTMIX(VMIX_BYTESWAP (inp[ip]));
tmp = (tmp * vol) / VMIX_VOL_SCALE;
*chbuf++ += tmp;
ip = (ip + portc->channels) % inmax;
/* VU meter */
if (tmp < 0)
tmp = -tmp;
if (tmp > vu)
vu = tmp;
}
if (ch < 2)
{ /* Save left/right VU meters */
vu = vu / 65536;
portc->vu[ch] = vu;
}
}
Finally save the state variables
portc->play_dma_pointer = (portc->play_dma_pointer + nsamples * frame_size * portc->channels) % dmap->bytes_in_use;