QTimer subclassed for timepoint functionality (allowing "timing" without drift)
QTimer's interface is currently only interval-based.
You start a timer... specifying an interval until timeout.
On timeout you restart the timer... with a new interval. And the restarting causes a few nanoseconds of drift.
QTimer timer;
timer.setSingleShot(true);
bool slow_interval = true; // if true: interval = 1 sec, else: interval = 0.5 sec
timer.setInterval( (slow_interval ? 1000 : 500) );
timer.start();
QObject::connect(&timer, &QTimer::timeout,
[&]() {
std::cout << "timepoint: " << QDateTime::currentMSecsSinceEpoch() << std::endl;
slow_interval = ! slow_interval; // toggle interval
const int interval = (slow_interval ? 1000 : 500);
timer.start(interval); // timer will eventually drift !!!!!!!!!!!!!
});Subclass QTimer to extend its interface to allow the use a timepoint-based interface.
Start the timer... specifying the timepoint-of-timeout (as milliseconds since Epoch [1 Jan 1970]).
On timeout you restart the timer... with a new definite timpoint-of-timeout. There is no drift between these timepoints, since they are absolute.
class TpTimer : public QTimer {
//...
};
TpTimer timer;
timer.setSingleShot(true);
bool slow_interval = true; // if true: interval = 1 sec, else: interval = 0.5 sec
timer.setInterval( (slow_interval ? 1000 : 500) );
QObject::connect(&timer, &QTimer::timeout,
[&]() {
std::cout << "millisSinceEpoch planned-alarm: " << timer.expiryTimePoint() << "\n"
"actual: "
<< TpTimer::nowTimePoint() << '\n' << std::endl;
slow_interval = ! slow_interval; // toggle interval
const int interval = (slow_interval ? 1000 : 500);
timer.startToTimePoint(timer.expiryTimePoint() + interval); // no drift !!!
});