Low performance, timer and label.

Loc888

@VRonin It says no matching function.

VRonin

@Loc888 I tested it on my machine Qt 5.10 MSVC2013 x64 Win7. What version of Qt are you running?

Loc888

@VRonin Desktop Qt 5.2.0 MinGW 32bit

VRonin

Then everything should work, you probably just have to enable C++11

add CONFIG += c++11 in your .pro file
re-run qmake

Loc888

@VRonin It's working, but i need it in MS. It happens because text need to be updated fast, and it cause the problem. If i just run the timer, it's look's fine, but i need to show the time in label..

J.Hilk

@Loc888 I think you need to be a bit more specific, with what is going on.

It's working, but i need it in MS. It happens because text need to be updated fast, and it cause the problem. If i just run the timer, it's look's fine, but i need to show the time in label..

Updating a QLabel's text shouldn't take seconds to update

to modify the code of @VRonin abit to display time and fast changes:

#include <QApplication>
#include <QTimer>
#include <QLabel>
#include <QTime>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QLabel mainWid;
    QTimer mainTimer;
    QObject::connect(&mainTimer,&QTimer::timeout,[&mainWid]()->void{
       mainWid.setText(QTime::currentTime().toString("hh.mm.ss.zz"));
    });
    mainTimer.start(10);
    mainWid.show();

    return a.exec();
}

Loc888

@J.Hilk I would like to use that, but i don't want current time, i want everything starting from 0.

J.Hilk

@Loc888
this code examples are for the purpose of trouble shooting.
But it's easy enought to adapt.

#include <QApplication>
#include <QTimer>
#include <QLabel>
#include <QTime>
#include <QElapsedTimer>
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QLabel mainWid;
    QTimer mainTimer;
    QTime time(0,0);
    QElapsedTimer actualTimePassed;
    QObject::connect(&mainTimer,&QTimer::timeout,[&mainWid, &time, &actualTimePassed]()->void{
        time = time.addMSecs(actualTimePassed.elapsed());
        actualTimePassed.start();
        mainWid.setText(time.toString("hh.mm.ss.zzz"));
    });
    actualTimePassed.start();
    mainTimer.start(10);
    mainWid.show();

    return a.exec();
}

VRonin

@Loc888 said in Low performance, timer and label.:

it's working, but i need it in MS

Unfortunately this is platform dependant. Best you could do is:

#include <QApplication>
#include <QTimer>
#include <QLabel>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QLabel mainWid;
    QTimer mainTimer;
    mainTimer.setTimerType(Qt::PreciseTimer);
    unsigned int counter = 0;
    QObject::connect(&mainTimer,&QTimer::timeout,[&mainWid,&counter]()->void{
        mainWid.setText(QObject::tr("%1 msec").arg(++counter));
        mainWid.repaint();
    });
    mainTimer.start(1);
    mainWid.show();
    return a.exec();
}

Please note, from http://doc.qt.io/qt-5/qt.html#TimerType-enum:

Precise timers try to keep millisecond accuracy

try != will, unfortunately

Loc888

@VRonin Maybe i expressed wrong, but i don't want it in Ms (the total), so 5500 = 5,5s, i want that pattern "mm.ss.zzz" or "mm.ss.zz" , but i want it to start from 0, not from the current time. Is any way to force it? (In sec, ther is no delay when the method update the text).

Loc888

@J.Hilk Guys,i tried J.Hilk code,and it's not working how it should.

It doesnt help me, it's working, but if i compare the timer to my windows time, the difference is arround 10s (after 2min test), it's too mutch.

Why it's happening?

Ps. I tried with "setTimerType(Qt::PreciseTimer);", but still doesn't help...

????????

mpergand

My turn ;)

QLabel label;
label.setGeometry(100,100,200,50);
 QTimer timer;
 QTime time;

 QObject::connect(&timer,&QTimer::timeout,[&time,&label](){
    QTime elapsed=QTime::fromMSecsSinceStartOfDay(time.elapsed());
    label.setText(elapsed.toString("mm:ss:zzz"));
    });

time.start();
timer.start(100);
label.show();

Loc888

@mpergand

It seems you are the winner... Why it's working?

I thought it's working, because you set the delay to 100ms, but even if i change it to 1ms, still working 100%.
I don't understand why this is working,and the other timers including my, are all retarded... Why it's happening?

And that's the text update method fault's, i tried to turn off the update, and just set the last result, and it's 100% accurate.

mpergand

I know by experience that to rely on a timer is all wrong.
You must rely on the system clock for good accuracy.

And that's the text update method fault's, i tried to turn off the update, and just set the last result, and it's 100% accurate.

Refresh 1000 times per sec is a heavy task, it consumes about 20% cpu on my machine and serves nothing.
Timers use the event loop and if the computer is doing heavy tasks, timers triggers might be lost.
Rely on event loops for a counter is definitely a bad idea.

Loc888

@mpergand Ok, how i can use it with Start, Stop, and Reset button? Because i am trying to move your code to another project, and work with buttons, but when i start the timer, it doesn't do anything.. Still be on 00:00:000, i run it ones, and it start from the actual minutes and seconds, then i modified your code to force it start from 0, and i broke something, now nothing is working...

Loc888

@mpergand Ok, nevermind, i am blind sometimes... I fix it.

I find the way to restart it, but i have some problems with

" time.fromString("05:00:000"); "

It's not working, how should i use that? Or how to stop the time and the timer, and re-start it again but from the last time? (I dont want to reset it when i press the stop button, and then start).

VRonin

You missed an argument and the fact that it's a static function: http://doc.qt.io/qt-5/qtime.html#fromString-1

time = QTime::fromString("05:00:000","mm:ss:zzz");

Have you considered QTimeEdit instead of QLabel?

Loc888

@VRonin Still reset when i press the start button, and when i stop and start,it starts from 0.
Comon, how to fix that? It's almost fixed.

koahnig

@Loc888 said in Low performance, timer and label.:

@VRonin Still reset when i press the start button, and when i stop and start,it starts from 0.
Comon, how to fix that? It's almost fixed.

I suggest that you are showing your actual code snippets and explain what you think they should do.

Above there are only code snippets from others, not a single snippet from you. Nobody knows what you have taken over into your code. Therefore nobody can give you sound advice.

JKSH

@Loc888 said in Low performance, timer and label.:

how to stop the time and the timer, and re-start it again but from the last time? (I dont want to reset it when i press the stop button, and then start).

The Qt timer classes don't have a built-in ability to resume timing like a stopwatch. This means you need to write extra logic to do it.

Start your QElapsedTimer. It starts counting from 0.
Call QElapsedTimer::elapsed() to find out how many milliseconds have passed since the timer was started.
When the user clicks the stop button, store the value of the elapsed time in a variable.
When the user clicks the start the button again, restart your QElapsedTimer. This makes it start from 0 again.
Add the value of the stored variable to QElapsedTimer::elapsed() to get your final stopwatch value.

@Loc888 said in Low performance, timer and label.:

Comon, how to fix that? It's almost fixed.

Since you have not shown your code at all, all the discussions in this thread is only to teach you how to use the time-related classes and functions. We cannot see how you have designed your program, so we cannot tell you how to "fix" your program.

You need to sit down and think through the logic and maths to implement the stopwatch.