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This file is almost the same than playmix.inc but uses simple linear interpolation algorithm for sample rate conversion.
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; double vol, step; double tmp;
Initial setup
step = (double) portc->rate / (double) mixer->play_engine.rate; #if 1
TODO: For some reason "trivial" conversion rations such as 4:1, 2:1, 1:2 and 1:4 don't work properly. As a workaround we add a tiny error to break the evil ratio. Need to find out why the algorithm doesn't work with such ratios.
if (step==4.0)step=4.0001; if (step==2.0)step=2.0001; if (step==0.5)step=0.5001; if (step==0.25)step=0.25001; #endif frame_size = sizeof (*inp); inmax = dmap->bytes_in_use / frame_size / portc->channels; inptr = (int)(portc->play_dma_pointer_src / frame_size / portc->channels); 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++)
{
double ip = inptr + (ch%used_channels);
double vu = portc->vu[ch % 2];
float *chbuf = eng->chbufs[ch+portc->play_choffs];
inp = (BUFFER_TYPE) dmap->dmabuf;
inp += ch;
i = portc->volume[ch%2];
vol = vmix_db_table[i / 5];
vu = vu / 255.0;
for (i = 0; i < nsamples; i++)
{
double frag, tmp_next;
int ip_next;
#if 0 && defined(SINE_DEBUG)
if (ch > 1)
tmp = 0.0;
else
tmp = sine_table[sine_phase[ch]];
sine_phase[ch] = (sine_phase[ch] + 1) % SINE_SIZE;
#else
Convert the sample to right endianess.
tmp = VMIX_BYTESWAP (inp[((int) ip) * portc->channels]);
/* perform linear interpolation */
ip_next = (((int) ip) + 1) % inmax;
tmp_next = VMIX_BYTESWAP (inp[ip_next * portc->channels]);
frag = ip - (int) ip; /* Pointer fraction */
tmp += (tmp_next - tmp) * frag;
tmp /= 2.0;
tmp = tmp * range;
#endif
tmp = tmp * vol;
*chbuf++ += tmp;
ip = ip + step;
if (ip > inmax)
ip -= inmax;
/* VU meter */
if (tmp < 0.0)
tmp = -tmp;
if (tmp > vu)
vu = tmp;
}
if (ch < 2)
{ /* Save left/right VU meters */
vu = vu * 255.0;
portc->vu[ch] = (int)vu;
}
}
Finally save the state variables
tmp = (nsamples * frame_size * portc->channels); tmp *= step; portc->play_dma_pointer_src = portc->play_dma_pointer_src + tmp; if (portc->play_dma_pointer_src > dmap->bytes_in_use) portc->play_dma_pointer_src -= dmap->bytes_in_use; portc->play_dma_pointer = (int)portc->play_dma_pointer_src; frame_size *= portc->channels; portc->play_dma_pointer = (portc->play_dma_pointer / frame_size) * frame_size;