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drawing shapes onto QPixmap with QPaintEvent

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  • H hobbyProgrammer

    @mrjj I implemented the code that you said I should try, but it doesn't raise the cc.

    mrjjM Offline
    mrjjM Offline
    mrjj
    Lifetime Qt Champion
    wrote on last edited by
    #11

    @hobbyProgrammer

    Ok. that i cannot guess.
    You can try with repaint() from mousePress.

    Also, in paintEvent
    this->update();
    Could cause infinite recursion so its not nice to call update from paintEvent

    H 1 Reply Last reply
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    • mrjjM mrjj

      @hobbyProgrammer

      Ok. that i cannot guess.
      You can try with repaint() from mousePress.

      Also, in paintEvent
      this->update();
      Could cause infinite recursion so its not nice to call update from paintEvent

      H Offline
      H Offline
      hobbyProgrammer
      wrote on last edited by
      #12

      @mrjj I removed the update and added the repaint, but it still didn't resolve the issue.

      mrjjM J.HilkJ 2 Replies Last reply
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      • H hobbyProgrammer

        @mrjj I removed the update and added the repaint, but it still didn't resolve the issue.

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

        @hobbyProgrammer

        Ok. then i really cant guess.
        Code seems fine and should work.

        H 1 Reply Last reply
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        • H hobbyProgrammer

          @mrjj I removed the update and added the repaint, but it still didn't resolve the issue.

          J.HilkJ Offline
          J.HilkJ Offline
          J.Hilk
          Moderators
          wrote on last edited by J.Hilk
          #14

          @hobbyProgrammer
          I would suggest calling the base implementation of mousepressevent as well

          void GraphicsView::mousePressEvent(QMouseEvent *event)
          {
             QGraphicsView::mousePressEvent(event);
          
              if(event->button() == Qt::LeftButton)
              {
                  QPointF point = mapToScene(event->pos());
                  double x = point.x();
                  double y = point.y();
                  qv_points << QPointF(x,y);
              }
              this->update();
          
          }
          

          Be aware of the Qt Code of Conduct, when posting : https://forum.qt.io/topic/113070/qt-code-of-conduct


          Q: What's that?
          A: It's blue light.
          Q: What does it do?
          A: It turns blue.

          1 Reply Last reply
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          • mrjjM mrjj

            @hobbyProgrammer

            Ok. then i really cant guess.
            Code seems fine and should work.

            H Offline
            H Offline
            hobbyProgrammer
            wrote on last edited by
            #15

            @mrjj It does work when I put another app on the forground such as google chrome and leave the app on the background. When I put the app on the foreground, it updates the coördinates.

            @J-Hilk unfortunately, that does not resolve my issue

            1 Reply Last reply
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            • H Offline
              H Offline
              hobbyProgrammer
              wrote on last edited by
              #16

              @mrjj is is perhaps better to use drawForeground and drawBackground for this issue, or wouldn't it matter?

              mrjjM 1 Reply Last reply
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              • H hobbyProgrammer

                @mrjj is is perhaps better to use drawForeground and drawBackground for this issue, or wouldn't it matter?

                mrjjM Offline
                mrjjM Offline
                mrjj
                Lifetime Qt Champion
                wrote on last edited by
                #17

                @hobbyProgrammer
                Hi
                well DrawForeground and DrawBackground is often used for Grid feature or
                similar. However, if you pixmap is sort of a background type, it would make sense but i cant promise it works better since i do not see why it would not
                call the paintEvent for the view. Or what it is you are seeing.

                Also since you do not seem to call QGraphicsView normal paint,
                i wonder if you dont use any of QGraphicsView features besides
                just drawing on it ?

                H 1 Reply Last reply
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                • mrjjM mrjj

                  @hobbyProgrammer
                  Hi
                  well DrawForeground and DrawBackground is often used for Grid feature or
                  similar. However, if you pixmap is sort of a background type, it would make sense but i cant promise it works better since i do not see why it would not
                  call the paintEvent for the view. Or what it is you are seeing.

                  Also since you do not seem to call QGraphicsView normal paint,
                  i wonder if you dont use any of QGraphicsView features besides
                  just drawing on it ?

                  H Offline
                  H Offline
                  hobbyProgrammer
                  wrote on last edited by
                  #18

                  @mrjj Hi,

                  All the code I used, I posted here so if it's not in this part of the code, it's nowhere in the code.
                  I'm going to try to recreate the project step by step, maybe I'll find the mistake.

                  mrjjM 1 Reply Last reply
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                  • H hobbyProgrammer

                    @mrjj Hi,

                    All the code I used, I posted here so if it's not in this part of the code, it's nowhere in the code.
                    I'm going to try to recreate the project step by step, maybe I'll find the mistake.

                    mrjjM Offline
                    mrjjM Offline
                    mrjj
                    Lifetime Qt Champion
                    wrote on last edited by mrjj
                    #19

                    @hobbyProgrammer
                    Hi
                    Just to be sure i understand the actual task.
                    You want to show an image and then draw points by clicking
                    on the image. These points should be "live" meaning they should not be combined with image but drawn on top of the image ?

                    Is it a requirement that the image can be zoomed and panned around and those points follow the scaling?

                    H 1 Reply Last reply
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                    • mrjjM mrjj

                      @hobbyProgrammer
                      Hi
                      Just to be sure i understand the actual task.
                      You want to show an image and then draw points by clicking
                      on the image. These points should be "live" meaning they should not be combined with image but drawn on top of the image ?

                      Is it a requirement that the image can be zoomed and panned around and those points follow the scaling?

                      H Offline
                      H Offline
                      hobbyProgrammer
                      wrote on last edited by
                      #20

                      @mrjj yes exactly! but when I zoom in and out I would like there to be a scrollbar so that I can view and edit the entire image and not just the upper part.

                      mrjjM 1 Reply Last reply
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                      • H hobbyProgrammer

                        @mrjj yes exactly! but when I zoom in and out I would like there to be a scrollbar so that I can view and edit the entire image and not just the upper part.

                        mrjjM Offline
                        mrjjM Offline
                        mrjj
                        Lifetime Qt Champion
                        wrote on last edited by
                        #21

                        @hobbyProgrammer

                        Well im asking as you use the GraphicsView in a (in my opinion) odd way
                        as you treat it like the QWidget paint.
                        Normally one would use
                        https://doc.qt.io/qt-5/qgraphicspixmapitem.html
                        for the image and and make a custom QGraphicsItem to handle the overlay points
                        and in other ways used the features of the QGraphicsScene/view.

                        Where are you seem to directly draw on the view as a normal Widget.

                        Its not criticism! i just wondered if you needed all of the QGraphicsScene/view stuff as doing with just a QWidget and paint is far more simple if
                        all the other features is not needed.

                        And when you just overwrite paint for view (as the code you shown), then you are not using ANY of the selection/grouping/scaling etc of the Graphics Framework.
                        So i had to ask :)

                        H 1 Reply Last reply
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                        • mrjjM mrjj

                          @hobbyProgrammer

                          Well im asking as you use the GraphicsView in a (in my opinion) odd way
                          as you treat it like the QWidget paint.
                          Normally one would use
                          https://doc.qt.io/qt-5/qgraphicspixmapitem.html
                          for the image and and make a custom QGraphicsItem to handle the overlay points
                          and in other ways used the features of the QGraphicsScene/view.

                          Where are you seem to directly draw on the view as a normal Widget.

                          Its not criticism! i just wondered if you needed all of the QGraphicsScene/view stuff as doing with just a QWidget and paint is far more simple if
                          all the other features is not needed.

                          And when you just overwrite paint for view (as the code you shown), then you are not using ANY of the selection/grouping/scaling etc of the Graphics Framework.
                          So i had to ask :)

                          H Offline
                          H Offline
                          hobbyProgrammer
                          wrote on last edited by
                          #22

                          @mrjj okay, but I still don't get how to use the QGraphicsScene/View now.
                          Do I make the ScrollArea a QGraphicsView and then load the QGraphicsPixmap into the QGraphicsView?

                          I don't really get the structure that is needed for this.

                          mrjjM 1 Reply Last reply
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                          • H hobbyProgrammer

                            @mrjj okay, but I still don't get how to use the QGraphicsScene/View now.
                            Do I make the ScrollArea a QGraphicsView and then load the QGraphicsPixmap into the QGraphicsView?

                            I don't really get the structure that is needed for this.

                            mrjjM Offline
                            mrjjM Offline
                            mrjj
                            Lifetime Qt Champion
                            wrote on last edited by
                            #23

                            @hobbyProgrammer

                            Hi
                            Normally the one would use QGraphicsPixmapItem
                            and maybe a custom item for the lines/polygon.
                            You would not need a ScrollArea

                            H 1 Reply Last reply
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                            • mrjjM mrjj

                              @hobbyProgrammer

                              Hi
                              Normally the one would use QGraphicsPixmapItem
                              and maybe a custom item for the lines/polygon.
                              You would not need a ScrollArea

                              H Offline
                              H Offline
                              hobbyProgrammer
                              wrote on last edited by
                              #24

                              @mrjj Okay so I tried to make a new graphicsview and this is the code.
                              It doesn't seem to load the pixmap.
                              It's probably a stupid mistake (I make them a lot), since I've wasted way too much time on this.

                              #include "graphicsview.h"
                              
                              GraphicsView::GraphicsView(QWidget *parent)
                                  : QGraphicsView(parent)
                              {
                                  scene = new QGraphicsScene(this);
                                  setScene(scene);
                              }
                              
                              void GraphicsView::open()
                              {
                                  filename = QFileDialog::getOpenFileName(this,tr("Open File"), QDir::currentPath(), tr("Image Files(*.png *.jpg *.jpeg)"));
                                  qDebug() << filename;
                                  QGraphicsPixmapItem *pixmap = scene->addPixmap(QPixmap(filename));
                                  update();
                              }
                              
                              1 Reply Last reply
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