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significantly reduce rounding error when doing framepos_t + BBT math

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git-svn-id: svn://localhost/ardour2/branches/3.0@10852 d708f5d6-7413-0410-9779-e7cbd77b26cf
This commit is contained in:
Paul Davis 2011-12-01 22:54:50 +00:00
parent bcaccc5ece
commit 93d8451d9e
1 changed files with 32 additions and 12 deletions
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44
libs/ardour/tempo.cc
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@ -1939,18 +1939,12 @@ TempoMap::bbt_subtract (const BBT_Time& start, const BBT_Time& decrement) const
framepos_t
TempoMap::framepos_plus_bbt (framepos_t pos, BBT_Time op) const
{
/* XXX: this is a little inaccurate as small errors are introduced
every time a probably-fractional product of something and
frames_per_beat is rounded. Other errors can be introduced
by op.ticks' integer nature.
*/
Metrics::const_iterator i;
const MeterSection* meter;
const MeterSection* m;
const TempoSection* tempo;
const TempoSection* t;
framecnt_t frames_per_beat;
double frames_per_beat;
meter = &first_meter ();
tempo = &first_tempo ();
@ -1986,9 +1980,11 @@ TempoMap::framepos_plus_bbt (framepos_t pos, BBT_Time op) const
frames_per_beat = tempo->frames_per_beat (_frame_rate, *meter);
uint64_t bars = 0;
while (op.bars) {
pos += llrint (frames_per_beat * meter->beats_per_bar());
bars++;
op.bars--;
/* check if we need to use a new metric section: has adding frames moved us
@ -1998,6 +1994,15 @@ TempoMap::framepos_plus_bbt (framepos_t pos, BBT_Time op) const
if (i != metrics->end()) {
if ((*i)->frame() <= pos) {
/* about to change tempo or meter, so add the
* number of frames for the bars we've just
* traversed before we change the
* frames_per_beat value.
*/
pos += llrint (frames_per_beat * (bars * meter->beats_per_bar()));
bars = 0;
if ((t = dynamic_cast<const TempoSection*>(*i)) != 0) {
tempo = t;
} else if ((m = dynamic_cast<const MeterSection*>(*i)) != 0) {
@ -2011,11 +2016,15 @@ TempoMap::framepos_plus_bbt (framepos_t pos, BBT_Time op) const
}
pos += llrint (frames_per_beat * (bars * meter->beats_per_bar()));
uint64_t beats = 0;
while (op.beats) {
/* given the current meter, have we gone past the end of the bar ? */
pos += frames_per_beat;
beats++;
op.beats--;
/* check if we need to use a new metric section: has adding frames moved us
@ -2025,6 +2034,15 @@ TempoMap::framepos_plus_bbt (framepos_t pos, BBT_Time op) const
if (i != metrics->end()) {
if ((*i)->frame() <= pos) {
/* about to change tempo or meter, so add the
* number of frames for the beats we've just
* traversed before we change the
* frames_per_beat value.
*/
pos += llrint (beats * frames_per_beat);
beats = 0;
if ((t = dynamic_cast<const TempoSection*>(*i)) != 0) {
tempo = t;
} else if ((m = dynamic_cast<const MeterSection*>(*i)) != 0) {
@ -2036,10 +2054,13 @@ TempoMap::framepos_plus_bbt (framepos_t pos, BBT_Time op) const
}
}
pos += llrint (beats * frames_per_beat);
if (op.ticks) {
if (op.ticks >= BBT_Time::ticks_per_beat) {
pos += frames_per_beat;
pos += llrint (frames_per_beat * ((op.ticks % (uint32_t) BBT_Time::ticks_per_beat) / (double) BBT_Time::ticks_per_beat));
pos += llrint (frames_per_beat + /* extra beat */
(frames_per_beat * ((op.ticks % (uint32_t) BBT_Time::ticks_per_beat) /
(double) BBT_Time::ticks_per_beat)));
} else {
pos += llrint (frames_per_beat * (op.ticks / (double) BBT_Time::ticks_per_beat));
}
@ -2130,7 +2151,6 @@ TempoMap::framewalk_to_beats (framepos_t pos, framecnt_t distance) const
frames_per_beat = tempo->frames_per_beat (_frame_rate, *meter);
}
}
}
return beats;