Problem : I have a plot covering over a 30 year period. At this range, QCPAxisTickerDateTime successsfully generates ticks at 1 year intervals.
My program also has a zoom feature which resets the range. However at a range of about 4 years and setTickCount() set for 50, the tick interval is about 1 month.
QCPAxisTickerDateTime though appears to skip tics for several months, leaving large gaps between ticks. The plot curve itself looks OK.
Root Cause : I debugged the problem and isolated it to qcustomplot.cpp, line 6739,
QCPAxisTickerDateTime::createTickVector(double tickStep, const QCPRange &range).
At line 6756, mTickOrigin = 0, i.e. Jan 1, 1970 0:00 UTC.
However, by default, keyToDateTime(mTickOrigin) translates this to local day/time.
In my case on the US Pacific West Coast, the local time is -8:00 UTC.
So keyToDateTime(mTickOrigin) translates the day/time to Dec 31, 1969 16:00
At line 6762, thisUniformDay = uniformDateTime.date().day(), which is set to 31.
In most cases, tickDateTime is usually the first day of the month.
This results in thisUniformDay - tickDateTime.date().day() > 15, which in turn causes the month to be pushed back to the previous month.
line 6766 tickDateTime = tickDateTime.addMonths(-1);
tickDateTime is then recalculated using the new month and thisUniformDay
line 6767, tickDateTime.setDate(QDate(tickDateTime.date().year(), tickDateTime.date().month(), thisUniformDay));
In most cases, there is no problem.
For example, tickDateTime = August 1, 2012 becomes July 31, 2012
But in some cases tickDateTime is recalculated to a month with less than 31 days
For example, tickDateTime = October 1, 2012 becomes September 31, 2012, which is an invalid date.
Therefore :
line 6768 result[ i ] = dateTimeToKey(tickDateTime); is set to 0
With the resulting tick set to 0, the tick is not displayed.
Work Around: The work around I settled on was to prevent invalid days being used.
I've modified the code, which includes extra variables for the MSVC debugger, starting at line 6739 :
QVector<double> QCPAxisTickerDateTime::createTickVector(double tickStep, const QCPRange &range)
{
QVector<double> result = QCPAxisTicker::createTickVector(tickStep, range);
if (!result.isEmpty())
{
if (mDateStrategy == dsUniformTimeInDay)
{
QDateTime uniformDateTime = keyToDateTime(mTickOrigin); // the time of this datetime will be set for all other ticks, if possible
QDateTime tickDateTime;
for (int i=0; i<result.size(); ++i)
{
tickDateTime = keyToDateTime(result.at(i));
tickDateTime.setTime(uniformDateTime.time());
result[i] = dateTimeToKey(tickDateTime);
}
} else if (mDateStrategy == dsUniformDayInMonth)
{
QDateTime uniformDateTime = keyToDateTime(mTickOrigin); // this day (in month) and time will be set for all other ticks, if possible
uniformDateTime.setTimeZone(QTimeZone(QTimeZone::UTC));
QDateTime tickDateTime;
int uniformDateTime_time_hour = uniformDateTime.time().hour();
int uniformDateTime_time_minute = uniformDateTime.time().minute();
int uniformDateTime_time_second = uniformDateTime.time().second();
int uniformDateTime_time_msec = uniformDateTime.time().msec();
int uniformDateTime_date_day = uniformDateTime.date().day();
int uniformDateTime_date_year = uniformDateTime.date().year();
int uniformDateTime_date_month = uniformDateTime.date().month();
int uniformDateTime_date_daysInMonth = uniformDateTime.date().daysInMonth();
int tickDateTime_time_hour;
int tickDateTime_time_minute;
int tickDateTime_time_second;
int tickDateTime_time_msec;
int tickDateTime_date_year;
int tickDateTime_date_month;
int tickDateTime_date_day;
int tickDateTime_date_daysInMonth;
for (int i=0; i<result.size(); ++i)
{
tickDateTime = keyToDateTime(result.at(i));
tickDateTime.setTime(uniformDateTime.time());
tickDateTime_date_daysInMonth = tickDateTime.date().daysInMonth();
int thisUniformDay;
if(uniformDateTime.date().day() <= tickDateTime.date().daysInMonth())
{
thisUniformDay = uniformDateTime.date().day();
}
else
{
thisUniformDay = tickDateTime.date().daysInMonth(); // don't exceed month (e.g. try to set day 31 in February)
}
tickDateTime_time_hour = tickDateTime.time().hour();
tickDateTime_time_minute = tickDateTime.time().minute();
tickDateTime_time_second = tickDateTime.time().second();
tickDateTime_time_msec = tickDateTime.time().msec();
tickDateTime_date_year = tickDateTime.date().year();
tickDateTime_date_month = tickDateTime.date().month();
tickDateTime_date_day = tickDateTime.date().day();
//if (thisUniformDay - tickDateTime.date().day() < -15) // with leap years involved, date month may jump backwards or forwards, and needs to be corrected before setting day
if (thisUniformDay - tickDateTime_date_day < -15) // with leap years involved, date month may jump backwards or forwards, and needs to be corrected before setting day
tickDateTime = tickDateTime.addMonths(1);
else if (thisUniformDay - tickDateTime_date_day > 15) // with leap years involved, date month may jump backwards or forwards, and needs to be corrected before setting day
tickDateTime = tickDateTime.addMonths(-1);
tickDateTime_time_hour = tickDateTime.time().hour();
tickDateTime_time_minute = tickDateTime.time().minute();
tickDateTime_time_second = tickDateTime.time().second();
tickDateTime_time_msec = tickDateTime.time().msec();
tickDateTime_date_year = tickDateTime.date().year();
tickDateTime_date_month = tickDateTime.date().month();
tickDateTime_date_day = tickDateTime.date().day();
bool tickDateTime_date_leap_year = ((tickDateTime_date_year % 4) == 0);
if ( (tickDateTime_date_month == 2) && tickDateTime_date_leap_year && ((tickDateTime_date_day > 29) || (thisUniformDay > 29)))
{
tickDateTime_date_day = 29;
tickDateTime.setDate(QDate(tickDateTime_date_year, tickDateTime_date_month, tickDateTime_date_day));
}
else if ((tickDateTime_date_month == 2) && ((tickDateTime_date_day > 28) || (thisUniformDay > 28)))
{
tickDateTime_date_day = 28;
tickDateTime.setDate(QDate(tickDateTime_date_year, tickDateTime_date_month, tickDateTime_date_day));
}
else if ( ((tickDateTime_date_month == 4) || (tickDateTime_date_month == 6)|| (tickDateTime_date_month == 9)|| (tickDateTime_date_month == 11))
&& ((tickDateTime_date_day > 28) || (thisUniformDay > 30)))
{
tickDateTime_date_day = 30;
tickDateTime.setDate(QDate(tickDateTime_date_year, tickDateTime_date_month, tickDateTime_date_day));
}
else
{
tickDateTime.setDate(QDate(tickDateTime_date_year, tickDateTime_date_month, thisUniformDay));
}
//tickDateTime.setDate(QDate(tickDateTime.date().year(), tickDateTime.date().month(), thisUniformDay));
tickDateTime_time_hour = tickDateTime.time().hour();
tickDateTime_time_minute = tickDateTime.time().minute();
tickDateTime_time_second = tickDateTime.time().second();
tickDateTime_time_msec = tickDateTime.time().msec();
tickDateTime_date_year = tickDateTime.date().year();
tickDateTime_date_month = tickDateTime.date().month();
tickDateTime_date_day = tickDateTime.date().day();
result[i] = dateTimeToKey(tickDateTime);
}
}
}
return result;
}