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Draw rectangle on QLabel

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  • dheerendraD Offline
    dheerendraD Offline
    dheerendra
    Qt Champions 2022
    wrote on last edited by
    #3

    Another way you can do is that, write a custom widget to paint your web-cam image, handle mouseEvent, use same paintEvent draw circle.

    Dheerendra
    @Community Service
    Certified Qt Specialist
    http://www.pthinks.com

    1 Reply Last reply
    0
    • KiraK Offline
      KiraK Offline
      Kira
      wrote on last edited by
      #4

      @jsulm : Thanks for the reply. My doubt was, as my QLabel on which i am showing the output of webcam is refreshing continuously with frame of images whether this circle will also get refreshed as it image is continuously changing

      mrjjM 1 Reply Last reply
      0
      • KiraK Kira

        @jsulm : Thanks for the reply. My doubt was, as my QLabel on which i am showing the output of webcam is refreshing continuously with frame of images whether this circle will also get refreshed as it image is continuously changing

        mrjjM Offline
        mrjjM Offline
        mrjj
        Lifetime Qt Champion
        wrote on last edited by
        #5

        @Kira
        Hi
        If you just replace the image with setPixmap then yes it replaces all you had drawn before,
        but if you override paintEvent and handle drawing yourself then
        you just draw image and then the circle ( from variable ) and new frames will not override it.

        Notice if you need to drag out a rect , this class
        http://doc.qt.io/qt-5/qrubberband.html
        is useful.

        1 Reply Last reply
        2
        • KiraK Offline
          KiraK Offline
          Kira
          wrote on last edited by
          #6

          Hello All,
          @mrjj @jsulm @dheerendra :

          Thanks for your reply everyone.
          I tried to implement the above functionality using QRubberband.
          I tried to follow an approach where i tried to implement the rubberband functionality on the QLabel
          using EventFilter.

          My problem is that my mousepress event works fine. But when go to mouse move event my code crashes.

          Sample code is given below:

          bool MainWindow::eventFilter(QObject *obj, QEvent *event)
          {
          if (event->type() == QEvent::MouseButtonPress)
          {
          QMouseEvent mouseEvent = static_cast<QMouseEvent>(event);
          statusBar()->showMessage(QString("Mouse move (%1,%2)").arg(mouseEvent->pos().x()).arg(mouseEvent->pos().y()));
          origin = mouseEvent->pos();
          if (!rubberBand)
          rubberBand = new QRubberBand(QRubberBand::Line, this);
          rubberBand->setGeometry(QRect(origin, QSize()));
          rubberBand->show();
          qDebug("Entered the Mousebutton press Event");
          }

          if (event->type() == QEvent::MouseMove)
          {
          qDebug("Entering the mouse move event");
          counter ++;
          qDebug()<<counter;
          QMouseEventmouseEvent = static_cast<QMouseEvent>(event);
          rubberBand->setGeometry(QRect(origin, mouseEvent->pos()).normalized()) // The code crashes at this line.
          qDebug("Completed the mouse move event");
          }
          return false;
          }

          Thanks in advance

          jsulmJ 1 Reply Last reply
          0
          • KiraK Kira

            Hello All,
            @mrjj @jsulm @dheerendra :

            Thanks for your reply everyone.
            I tried to implement the above functionality using QRubberband.
            I tried to follow an approach where i tried to implement the rubberband functionality on the QLabel
            using EventFilter.

            My problem is that my mousepress event works fine. But when go to mouse move event my code crashes.

            Sample code is given below:

            bool MainWindow::eventFilter(QObject *obj, QEvent *event)
            {
            if (event->type() == QEvent::MouseButtonPress)
            {
            QMouseEvent mouseEvent = static_cast<QMouseEvent>(event);
            statusBar()->showMessage(QString("Mouse move (%1,%2)").arg(mouseEvent->pos().x()).arg(mouseEvent->pos().y()));
            origin = mouseEvent->pos();
            if (!rubberBand)
            rubberBand = new QRubberBand(QRubberBand::Line, this);
            rubberBand->setGeometry(QRect(origin, QSize()));
            rubberBand->show();
            qDebug("Entered the Mousebutton press Event");
            }

            if (event->type() == QEvent::MouseMove)
            {
            qDebug("Entering the mouse move event");
            counter ++;
            qDebug()<<counter;
            QMouseEventmouseEvent = static_cast<QMouseEvent>(event);
            rubberBand->setGeometry(QRect(origin, mouseEvent->pos()).normalized()) // The code crashes at this line.
            qDebug("Completed the mouse move event");
            }
            return false;
            }

            Thanks in advance

            jsulmJ Offline
            jsulmJ Offline
            jsulm
            Lifetime Qt Champion
            wrote on last edited by jsulm
            #7

            @Kira Shouldn't it be

            QMouseEvent *mouseEvent = static_cast<QMouseEvent*>(event);
            rubberBand->setGeometry(QRect(origin, mouseEvent->pos()).normalized())) ;
            

            Was rubberBand initialized?

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

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            0
            • KiraK Offline
              KiraK Offline
              Kira
              wrote on last edited by Kira
              #8

              @jsulm : thanks for the reply it worked like a charm.
              The issue got resolved now i can draw rubberband easily.

              The rubbandband get drawn easily when i assign QRubberband to main window widget.
              But when i try to assign it to QLabel there is issue with the drawing of rubberband.
              I search on the above topic and came to know it is because of difference of the co-ordinates of window and label and i have to map it globally using the below link:
              https://stackoverflow.com/questions/16527248/qrubberband-on-a-definite-label
              But the problem still exist and i am not able to draw the rectangle.
              //Example code:
              void MainWindow::mousePressEvent(QMouseEvent *event){

              mypoint = ui->label->mapFromGlobal(this->mapToGlobal(event->pos()));
              // mypoint = ui->label->mapFrom(this, event->pos());
              // mypoint = this->mapTo(ui->label, event->pos());
              if(rubberBand == 0) // You should add this to not have a memory leak
                  rubberBand = new QRubberBand(QRubberBand::Rectangle, ui->label_2);//new rectangle band
              rubberBand->setGeometry(QRect(mypoint, ui->label_2->size()));
              rubberBand->show();
              

              }
              After following the above approach,
              When i click the mouse inside the label the whole rubberband gets drawn without even moving the cursor.

              Another approach would be making a custom QLabel and implement the mouse co-ordinate in it but wanted to know if its possible using above approach

              jsulmJ 1 Reply Last reply
              0
              • KiraK Kira

                @jsulm : thanks for the reply it worked like a charm.
                The issue got resolved now i can draw rubberband easily.

                The rubbandband get drawn easily when i assign QRubberband to main window widget.
                But when i try to assign it to QLabel there is issue with the drawing of rubberband.
                I search on the above topic and came to know it is because of difference of the co-ordinates of window and label and i have to map it globally using the below link:
                https://stackoverflow.com/questions/16527248/qrubberband-on-a-definite-label
                But the problem still exist and i am not able to draw the rectangle.
                //Example code:
                void MainWindow::mousePressEvent(QMouseEvent *event){

                mypoint = ui->label->mapFromGlobal(this->mapToGlobal(event->pos()));
                // mypoint = ui->label->mapFrom(this, event->pos());
                // mypoint = this->mapTo(ui->label, event->pos());
                if(rubberBand == 0) // You should add this to not have a memory leak
                    rubberBand = new QRubberBand(QRubberBand::Rectangle, ui->label_2);//new rectangle band
                rubberBand->setGeometry(QRect(mypoint, ui->label_2->size()));
                rubberBand->show();
                

                }
                After following the above approach,
                When i click the mouse inside the label the whole rubberband gets drawn without even moving the cursor.

                Another approach would be making a custom QLabel and implement the mouse co-ordinate in it but wanted to know if its possible using above approach

                jsulmJ Offline
                jsulmJ Offline
                jsulm
                Lifetime Qt Champion
                wrote on last edited by
                #9

                @Kira said in Draw rectangle on QLabel:

                void MainWindow::mousePressEvent(QMouseEvent *event)

                You're overwriting mousePressEvent in MainWindow but actually you should do it only for the label, right? You should subclass QLabel and override mousePressEvent there.

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

                1 Reply Last reply
                1
                • KiraK Offline
                  KiraK Offline
                  Kira
                  wrote on last edited by
                  #10

                  @jsulm : Yes you are correct. But is there any way in which i can implement it in mouse event of the main window instead of creating the subclass of the QLabel as mentioned in the link by mapping the co-ordinates.

                  jsulmJ 1 Reply Last reply
                  0
                  • KiraK Kira

                    @jsulm : Yes you are correct. But is there any way in which i can implement it in mouse event of the main window instead of creating the subclass of the QLabel as mentioned in the link by mapping the co-ordinates.

                    jsulmJ Offline
                    jsulmJ Offline
                    jsulm
                    Lifetime Qt Champion
                    wrote on last edited by
                    #11

                    @Kira Well, you need to check whether the user actually clicked inside the label or not.

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

                    1 Reply Last reply
                    1
                    • KiraK Offline
                      KiraK Offline
                      Kira
                      wrote on last edited by
                      #12

                      @jsulm : can you please elaborate the approach. Because currently i am clicking inside the qlable and drawing the rubberband

                      mrjjM 1 Reply Last reply
                      0
                      • KiraK Kira

                        @jsulm : can you please elaborate the approach. Because currently i am clicking inside the qlable and drawing the rubberband

                        mrjjM Offline
                        mrjjM Offline
                        mrjj
                        Lifetime Qt Champion
                        wrote on last edited by mrjj
                        #13

                        @Kira

                        Hi
                        If you get mouseEvents to mainwindow, the x,y coordinates will be for the main window.
                        so when you press buttons, you need to use something like
                        http://doc.qt.io/qt-5/qapplication.html#widgetAt
                        and check if over the label.

                        But why do you want this ?
                        It will just be more complex than letting QLabel do it
                        You will also need to map coordinates as else it wont draw where u press as mainwindows x,Y is not the same
                        for label. so you must alter the x,y to draw inside QLabel.

                        1 Reply Last reply
                        1
                        • KiraK Offline
                          KiraK Offline
                          Kira
                          wrote on last edited by
                          #14

                          @jsulm @mrjj : Guys thanks for your support. Got the issue resolved.
                          Actually there was issue with the mouse drag functionality where i was passing the event of the main widget.
                          It got resolved by mapping the coordinates of the mainwindow to global coordinate system.

                          Will implement the functionality by creating subclass of the label and implement the rubberband as stated earlier as the correct approach.

                          Just wanted to see whether the implementation is possible by this approach.

                          Thanks again for your help and support.

                          1 Reply Last reply
                          1
                          • mrjjM Offline
                            mrjjM Offline
                            mrjj
                            Lifetime Qt Champion
                            wrote on last edited by
                            #15

                            Super :)
                            for at quick start, u could use
                            https://wiki.qt.io/Clickable_QLabel

                            1 Reply Last reply
                            0
                            • KiraK Offline
                              KiraK Offline
                              Kira
                              wrote on last edited by
                              #16

                              @mrjj : thanks buddy.
                              Best supportive forum with best people and special thanks to @SGaist

                              1 Reply Last reply
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