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Resizing mainwindow using resizeEvent works very slow

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  • ? A Former User

    Hi,
    My Qt widget has a function to draw a line based on point (x, y) input from text file. I want to draw a line even when the window is resized. Everything works fine. I get the right coordinate when the window is maximized or minimized. However, the process is very slow. To maximize or minimize the window, the program will stuck at appx 4sec before it's maximized(minimized) and starts drawing again.

    Are there any way that I can up the speed of the resizeEvent?

    In my Qt widget, I have a function to read from text file, calculate the point (x, y) then write to text file.

    drawpath.cpp

    void DrawPath::drawPath(QString inFile, QString outFile, float width, float height)
    {
        readPosition(inFile);
        calculatedXY(someVector, width, height);
        writePosition(outFile, latLongPointVector);
    }
    

    resizeEvent is called through mainwindow.

    mainwindow.cpp

    void MainWindow::resizeEvent(QResizeEvent *event)
    {
    
        //scaled window size
        scaledWidth = double(event->size().width())/360.0;
        scaledHeight = double(event->size().height())/180.0;
    
        QString inFile = ":/input.txt";
        QString outFile = "output.txt";
    
        //set label window size
        ui->label->setGeometry(0, 0, 360*scaledWidth, 180*scaledHeight);
    
        //set draworbit window size
        path->drawPath(inFile, outFile, scaledWidth, scaledHeight);
        path->setGeometry(0, 0, 360*scaledWidth, 180*scaledHeight);
    }
    

    Thank you.

    Edit: the program will be used for a realtime (x, y) calculation so I need a fast working resize window.

    kshegunovK Offline
    kshegunovK Offline
    kshegunov
    Moderators
    wrote on last edited by kshegunov
    #11

    @soloespresso

    Edit: the program will be used for a realtime (x, y) calculation so I need a fast working resize window.

    If you want a "realtime" behavior, then thread the IO! It's not the QWidget::resizeEvent's job to read files and do (complicated) calculations. In your worker thread or main thread (by means of scheduling, but it's better to actually thread the operation) do the calculations and update a couple of fields. Then in the resize or paint events do the bare minimum of setting the geometry or painting the data. Events are queued and no event will be processed if the last one hasn't finished, so a slow resize event processing will cause your application to hang, not update widgets and not respond to user input, not process sockets or timers!

    DrawPath::readPosition is heavy (it reads a whole file), as @jsulm already suspected, and you do that in the event function(s), so everything is waiting for the IO to complete.

    Kind regards.

    Read and abide by the Qt Code of Conduct

    ? 1 Reply Last reply
    0
    • ? A Former User

      @jsulm said:

      Well, I don't know how readPosition() is implemented. But in general if the data in the file is static you should read that file only once (for example when your application is starting). To me it looks like you're doing it each time drawPath() is called.

      so here is my readPosition()

      void DrawPath::readPosition(QString inFile_)
      {
          //read from text file
          QFile file(inFile_);
          if(!file.open(QIODevice::ReadOnly | QIODevice::Text)){
              qDebug() << "error: unable to open...";
          }
      
          QTextStream in(&file);
      
          while(!in.atEnd()){
              QString lineData = in.readLine();
              QStringList listData = lineData.split("\t");
      
              someX << listData[4].toFloat();
              someY << listData[5].toFloat();
          }
      
          for(int i = 0; i < someX.size()-1; i++){
      
              //collect vector data into coordinate(x,y)
              xyPos.setX(someX[i]);
              xyPos.setY(someY[i]);
      
              //create vector of coordinate(x, y)
              xyPosVector.append(xyPos);
          }
      
          qDebug() << "Successfully loaded!";
      
          file.close();
      }
      

      At the moment, the data is static but it will be updated maybe daily for the complete version of the program. I would like to know if it's gonna be lagged.

      jsulmJ Offline
      jsulmJ Offline
      jsulm
      Lifetime Qt Champion
      wrote on last edited by
      #12

      @soloespresso readPosition() does not set someVector!
      If the change frequency of the file is so low then you should not read it all the time - it's just wasted time. You can use QFileSystemWatcher class to detect changes in this file and then reread it.

      https://forum.qt.io/topic/113070/qt-code-of-conduct

      ? 1 Reply Last reply
      0
      • kshegunovK kshegunov

        @soloespresso

        Edit: the program will be used for a realtime (x, y) calculation so I need a fast working resize window.

        If you want a "realtime" behavior, then thread the IO! It's not the QWidget::resizeEvent's job to read files and do (complicated) calculations. In your worker thread or main thread (by means of scheduling, but it's better to actually thread the operation) do the calculations and update a couple of fields. Then in the resize or paint events do the bare minimum of setting the geometry or painting the data. Events are queued and no event will be processed if the last one hasn't finished, so a slow resize event processing will cause your application to hang, not update widgets and not respond to user input, not process sockets or timers!

        DrawPath::readPosition is heavy (it reads a whole file), as @jsulm already suspected, and you do that in the event function(s), so everything is waiting for the IO to complete.

        Kind regards.

        ? Offline
        ? Offline
        A Former User
        wrote on last edited by
        #13

        @kshegunov said:

        If you want a "realtime" behavior, then thread the IO!

        And ow can I do that?

        I have tried calling only the function to calculate (x, y) without calling drawPath() in resizeEvent() something like this

        path->calculatedXY(someVector, width, height);
        

        but it gives me Runtime Error and "index out of range" for the vector used in that function.

        kshegunovK 1 Reply Last reply
        0
        • ? A Former User

          @kshegunov said:

          If you want a "realtime" behavior, then thread the IO!

          And ow can I do that?

          I have tried calling only the function to calculate (x, y) without calling drawPath() in resizeEvent() something like this

          path->calculatedXY(someVector, width, height);
          

          but it gives me Runtime Error and "index out of range" for the vector used in that function.

          kshegunovK Offline
          kshegunovK Offline
          kshegunov
          Moderators
          wrote on last edited by kshegunov
          #14

          @soloespresso said:

          And ow can I do that?

          Look here for an introduction.

          but it gives me Runtime Error and "index out of range" for the vector used in that function.

          See @jsulm's explanation as to why this is happening.
          Additionally your for loop is wrong:

          for (int i = 0; i < someX.size()-1; i++)  {
          

          this skips the last element in the vector.

          Kind regards.

          Read and abide by the Qt Code of Conduct

          ? 1 Reply Last reply
          0
          • jsulmJ jsulm

            @soloespresso readPosition() does not set someVector!
            If the change frequency of the file is so low then you should not read it all the time - it's just wasted time. You can use QFileSystemWatcher class to detect changes in this file and then reread it.

            ? Offline
            ? Offline
            A Former User
            wrote on last edited by
            #15

            @jsulm

            @jsulm said:

            @soloespresso readPosition() does not set someVector!

            I have some other functions in between. The readPosition() I posted is to give an idea what readPosition() does which is extract the data and keep them in a vector.

            If the change frequency of the file is so low then you should not read it all the time - it's just wasted time. You can use QFileSystemWatcher class to detect changes in this file and then reread it.

            OK, I will take a look on that.

            1 Reply Last reply
            0
            • kshegunovK kshegunov

              @soloespresso said:

              And ow can I do that?

              Look here for an introduction.

              but it gives me Runtime Error and "index out of range" for the vector used in that function.

              See @jsulm's explanation as to why this is happening.
              Additionally your for loop is wrong:

              for (int i = 0; i < someX.size()-1; i++)  {
              

              this skips the last element in the vector.

              Kind regards.

              ? Offline
              ? Offline
              A Former User
              wrote on last edited by
              #16

              @kshegunov said:

              @soloespresso said:

              And ow can I do that?

              Look here for an introduction.

              Ok, I will take a look.

              but it gives me Runtime Error and "index out of range" for the vector used in that function.

              See @jsulm's explanation as to why this is happening.
              Additionally your for loop is wrong:

              for (int i = 0; i < someX.size()-1; i++)  {
              

              this skips the last element in the vector.

              Kind regards.

              Right!!! I didn't see it. Thank you.

              1 Reply Last reply
              0
              • ? Offline
                ? Offline
                A Former User
                wrote on last edited by
                #17
                for (int i = 0; i < someX.size()-1; i++)  {
                

                fix this but still Runtime Error and "index out of range".

                I will check QFileSystemWatcher and thread after.

                kshegunovK 1 Reply Last reply
                0
                • ? A Former User
                  for (int i = 0; i < someX.size()-1; i++)  {
                  

                  fix this but still Runtime Error and "index out of range".

                  I will check QFileSystemWatcher and thread after.

                  kshegunovK Offline
                  kshegunovK Offline
                  kshegunov
                  Moderators
                  wrote on last edited by
                  #18

                  @soloespresso

                  fix this but still Runtime Error and "index out of range".

                  This hasn't anything to do with your error, it was just an observation. As to the assertion (which I'm assuming your code is failing), you should track that in the debugger.

                  Read and abide by the Qt Code of Conduct

                  ? 1 Reply Last reply
                  0
                  • kshegunovK kshegunov

                    @soloespresso

                    fix this but still Runtime Error and "index out of range".

                    This hasn't anything to do with your error, it was just an observation. As to the assertion (which I'm assuming your code is failing), you should track that in the debugger.

                    ? Offline
                    ? Offline
                    A Former User
                    wrote on last edited by
                    #19

                    @kshegunov said:

                    @soloespresso

                    fix this but still Runtime Error and "index out of range".

                    This hasn't anything to do with your error, it was just an observation. As to the assertion (which I'm assuming your code is failing), you should track that in the debugger.

                    So let me make sure if what I am doing is ok for Qt.
                    I have drawPath() in QWidget.

                    void DrawPath::drawPath(QString inFile, QString outFile, float width, float height)
                    {
                        readPosition(inFile);
                        calculatedXY(someVector, width, height);
                        writePosition(outFile, latLongPointVector);
                    }
                    

                    Can I call calculatedXY(someVector, width, height); outside drawPath() in resizeEvent() like this?

                    void MainWindow::resizeEvent(QResizeEvent *event)
                    {
                    
                        //scaled window size
                        scaledWidth = double(event->size().width())/360.0;
                        scaledHeight = double(event->size().height())/180.0;
                    
                        //QString inFile = ":/input.txt";
                        //QString outFile = "output.txt";
                    
                        //set label window size
                        ui->label->setGeometry(0, 0, 360*scaledWidth, 180*scaledHeight);
                    
                        //set draworbit window size
                        //path->drawPath(inFile, outFile, scaledWidth, scaledHeight);
                        path->calculatedXY(someVector, scaledWidth, scaledHeight);
                        path->setGeometry(0, 0, 360*scaledWidth, 180*scaledHeight);
                    }
                    
                    1 Reply Last reply
                    0
                    • kshegunovK Offline
                      kshegunovK Offline
                      kshegunov
                      Moderators
                      wrote on last edited by
                      #20

                      @soloespresso
                      No one is preventing you from calling calculatedXY(), but if it's a good design choice really depends what that function actually does.

                      Read and abide by the Qt Code of Conduct

                      ? 1 Reply Last reply
                      0
                      • kshegunovK kshegunov

                        @soloespresso
                        No one is preventing you from calling calculatedXY(), but if it's a good design choice really depends what that function actually does.

                        ? Offline
                        ? Offline
                        A Former User
                        wrote on last edited by
                        #21

                        @kshegunov said:

                        @soloespresso
                        No one is preventing you from calling calculatedXY(), but if it's a good design choice really depends what that function actually does.

                        Thank you for the confirmation.
                        Because calling drawPath() will call readPosition(), calculatedXY() and writePosition(), calling calculatedXY() directly will prevent resizeEvent() to reread the text file.

                        But this give me that Runtime Error and "index out of range" which I will debug later.

                        Now the problem is how to draw the line? I use paintEvent() to draw a line and the function is called when drawPath() is called.

                        1 Reply Last reply
                        0
                        • jsulmJ Offline
                          jsulmJ Offline
                          jsulm
                          Lifetime Qt Champion
                          wrote on last edited by
                          #22

                          "Now the problem is how to draw the line?" - what is the problem with that? When paintEvent() is called you draw the line.

                          https://forum.qt.io/topic/113070/qt-code-of-conduct

                          ? 1 Reply Last reply
                          0
                          • jsulmJ jsulm

                            "Now the problem is how to draw the line?" - what is the problem with that? When paintEvent() is called you draw the line.

                            ? Offline
                            ? Offline
                            A Former User
                            wrote on last edited by
                            #23

                            @jsulm said:

                            "Now the problem is how to draw the line?" - what is the problem with that? When paintEvent() is called you draw the line.

                            But then it means paintEvent() is called directly in resizeEvent()?
                            Is something like the code below possible?

                            void MainWindow::resizeEvent(QResizeEvent *event)
                            {
                            
                                //scaled window size
                                scaledWidth = double(event->size().width())/360.0;
                                scaledHeight = double(event->size().height())/180.0;
                            
                                //QString inFile = ":/input.txt";
                                //QString outFile = "output.txt";
                            
                                //set label window size
                                ui->label->setGeometry(0, 0, 360*scaledWidth, 180*scaledHeight);
                            
                                //set draworbit window size
                                //path->drawPath(inFile, outFile, scaledWidth, scaledHeight);
                                path->calculatedXY(someVector, scaledWidth, scaledHeight);
                                path->paintEvent();
                                path->setGeometry(0, 0, 360*scaledWidth, 180*scaledHeight);
                            }
                            
                            1 Reply Last reply
                            0
                            • jsulmJ Offline
                              jsulmJ Offline
                              jsulm
                              Lifetime Qt Champion
                              wrote on last edited by
                              #24

                              No, paintEvent() is called by Qt whenever a repaint is needed.
                              For example it is called after resizing a widget (as stated in documentation).

                              https://forum.qt.io/topic/113070/qt-code-of-conduct

                              ? 1 Reply Last reply
                              1
                              • jsulmJ jsulm

                                No, paintEvent() is called by Qt whenever a repaint is needed.
                                For example it is called after resizing a widget (as stated in documentation).

                                ? Offline
                                ? Offline
                                A Former User
                                wrote on last edited by
                                #25

                                @jsulm ok. sorry for a dumb question. I have tried it before but it didn't work so I wasn't sure if I understand how it works correctly.

                                So I tried calling the calculatedXY() directly in resizeEvent(), the line is drawn but not scaled when window is maximized. It is scaled only when I call the whole drawPath().

                                However, even calling directly calculatedXY() in resizeEvent(), the lag persists. Still appx 4 secs delay....

                                I have tried changing the size of the background img, even removed it, but still get the same result. I have no idea what could be a reason....

                                1 Reply Last reply
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