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    Unsolved Draw basic Axes on QPixmap ?

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    qpixmap qchart qlabel axis plot
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    • R
      R-P-H last edited by

      Hi,

      I have a QPixmap image that I put inside a label in Qt using ui->label->setPixmap(). I simply want to add some axes to the image with just basic tick marks, values and maybe axes labels. Everything I have seen so far is overly complicated using custom charts etc.

      Is there any easy way I can draw some simple axes onto the image and display it in the label ? Or can I draw the axis onto the label and overlay the image ? Or can I overlay the image onto an axes image already set in the label ?

      I'm really not sure how to go about this easily. Any suggestions ? Thanks.

      Pl45m4 J.Hilk A 3 Replies Last reply Reply Quote 0
      • Pl45m4
        Pl45m4 @R-P-H last edited by

        @r-p-h

        Why it has to be a label? QLabels are not supposed to have axis, so I guess there's not an "easy" way.

        Why dont you use QChartView? https://doc.qt.io/qt-5/qchartview.html


        If debugging is the process of removing software bugs, then programming must be the process of putting them in.

        ~E. W. Dijkstra

        R 1 Reply Last reply Reply Quote 0
        • J.Hilk
          J.Hilk Moderators @R-P-H last edited by

          hi @r-p-h

          If, you're dead set on using a QLabel,
          than one option would be, SubClassing QLabel, over write QPaintEvent.
          Inside the QPaintEvent, draw first the Image and than the "axis"

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

          Qt Needs YOUR vote: https://bugreports.qt.io/browse/QTQAINFRA-4121


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

          1 Reply Last reply Reply Quote 1
          • R
            R-P-H @Pl45m4 last edited by

            @pl45m4 said in Draw basic Axes on QPixmap ?:

            @r-p-h

            Why it has to be a label? QLabels are not supposed to have axis, so I guess there's not an "easy" way.

            Why dont you use QChartView? https://doc.qt.io/qt-5/qchartview.html

            It definitely doesn't have to be a QLabel. I'm just looking for the easiest most efficient way possible. In my QT Creator, there is no ChartView widget. Also, how would I display my pixmap image inside the chart ?

            @j-hilk said in Draw basic Axes on QPixmap ?:

            hi @r-p-h

            If, you're dead set on using a QLabel,
            than one option would be, SubClassing QLabel, over write QPaintEvent.
            Inside the QPaintEvent, draw first the Image and than the "axis"

            I am not dead-set on using QLabel, what would be the easiest ? Thanks.

            Pl45m4 1 Reply Last reply Reply Quote 0
            • Pl45m4
              Pl45m4 @R-P-H last edited by Pl45m4

              @r-p-h

              A ChartView, but as you already said, you have to create it on runtime, because it`s not a Widget in Qt Designer.


              If debugging is the process of removing software bugs, then programming must be the process of putting them in.

              ~E. W. Dijkstra

              R Pl45m4 2 Replies Last reply Reply Quote 1
              • R
                R-P-H @Pl45m4 last edited by

                @pl45m4 said in Draw basic Axes on QPixmap ?:

                @r-p-h

                A ChartView, but as you already said, you have to create it on runtime, because it`s not a Widget in Qt Designer.

                But is it possible to set the plot to a QPixmap image ?

                Pl45m4 1 Reply Last reply Reply Quote 0
                • Pl45m4
                  Pl45m4 @R-P-H last edited by Pl45m4

                  @r-p-h

                  Something like:

                  QPixmap pm(chartView->size());
                  chartView->render(&pm);
                  

                  Or

                  QPixmap pm = chartView->grab();
                  

                  What is your real goal? If you use a QChartView it displays your plot. Then you dont need a QPixmap or QLabel.
                  Do you want to save your plot to file or just show it?


                  If debugging is the process of removing software bugs, then programming must be the process of putting them in.

                  ~E. W. Dijkstra

                  R 1 Reply Last reply Reply Quote 0
                  • R
                    R-P-H @Pl45m4 last edited by

                    @pl45m4 said in Draw basic Axes on QPixmap ?:

                    @r-p-h

                    Something like:

                    QPixmap pm(chartView->size());
                    chartView->render(&pm);
                    

                    Or

                    QPixmap pm = chartView->grab();
                    

                    What is your real goal? If you use a QChartView it displays your plot. Then you dont need a QPixmap or QLabel.
                    Do you want to save your plot to file or just show it?

                    I have a QPixmap image. I need to display it on screen with axes...that is all.

                    J.Hilk 1 Reply Last reply Reply Quote 0
                    • J.Hilk
                      J.Hilk Moderators @R-P-H last edited by

                      @r-p-h than I would suggest to do what I said, previously

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

                      Qt Needs YOUR vote: https://bugreports.qt.io/browse/QTQAINFRA-4121


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

                      R 1 Reply Last reply Reply Quote 0
                      • R
                        R-P-H @J.Hilk last edited by

                        @j-hilk said in Draw basic Axes on QPixmap ?:

                        @r-p-h than I would suggest to do what I said, previously

                        Ok, but how do I go about inserting a QChartView where I want it in the GUI because as you said it isn't available as a widget in QTDesigner and my GUI is in "grid" layout...

                        J.Hilk 1 Reply Last reply Reply Quote 0
                        • J.Hilk
                          J.Hilk Moderators @R-P-H last edited by

                          @r-p-h
                          you're mixing myself and @Pl45m4 ;)

                          I said subclassing QLabel

                          #include <QApplication>
                          #include <QLabel>
                          #include <QPainter>
                          #include <QDebug>
                          
                          class myLabel : public QLabel
                          {
                          public:
                              explicit myLabel(QWidget *parent = nullptr) : QLabel(parent) {
                                  QImage img(200,200, QImage::Format_RGB888);
                                  img.fill(Qt::green);
                                  m_pixmap = QPixmap::fromImage(img);
                              }
                          
                          private:
                              QPixmap m_pixmap;
                          protected:
                              virtual void paintEvent(QPaintEvent *event)override{
                                  QLabel::paintEvent(event);//Basic drawing of the Parent class -> styles etc
                                  QPainter p(this);
                          
                                  p.drawPixmap(0,0,width(), height(),m_pixmap);
                                  p.setPen(QPen(Qt::red));
                                  p.drawLine(QPointF(10,0), QPointF(10, height()));
                                  p.drawLine(QPointF(0, height() - 10), QPointF(width(), height() -10));
                              }
                          };
                          
                          
                          int main(int argc, char *argv[])
                          {
                          
                              QApplication a(argc, argv);
                          
                              myLabel m;
                              m.resize(400,400);
                              m.show();
                          
                              return  a.exec();
                          }
                          

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

                          Qt Needs YOUR vote: https://bugreports.qt.io/browse/QTQAINFRA-4121


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

                          R 1 Reply Last reply Reply Quote 3
                          • R
                            R-P-H @J.Hilk last edited by

                            @j-hilk said in Draw basic Axes on QPixmap ?:

                            @r-p-h
                            you're mixing myself and @Pl45m4 ;)

                            I said subclassing QLabel

                            #include <QApplication>
                            #include <QLabel>
                            #include <QPainter>
                            #include <QDebug>
                            
                            class myLabel : public QLabel
                            {
                            public:
                                explicit myLabel(QWidget *parent = nullptr) : QLabel(parent) {
                                    QImage img(200,200, QImage::Format_RGB888);
                                    img.fill(Qt::green);
                                    m_pixmap = QPixmap::fromImage(img);
                                }
                            
                            private:
                                QPixmap m_pixmap;
                            protected:
                                virtual void paintEvent(QPaintEvent *event)override{
                                    QLabel::paintEvent(event);//Basic drawing of the Parent class -> styles etc
                                    QPainter p(this);
                            
                                    p.drawPixmap(0,0,width(), height(),m_pixmap);
                                    p.setPen(QPen(Qt::red));
                                    p.drawLine(QPointF(10,0), QPointF(10, height()));
                                    p.drawLine(QPointF(0, height() - 10), QPointF(width(), height() -10));
                                }
                            };
                            
                            
                            int main(int argc, char *argv[])
                            {
                            
                                QApplication a(argc, argv);
                            
                                myLabel m;
                                m.resize(400,400);
                                m.show();
                            
                                return  a.exec();
                            }
                            

                            Sorry you're correct, I was confusing the two of you. Why does this need to be in a class format like how you showed ? Can I not directly paint the QLabel ? Also I usually resize the image to the size of the label before putting it in QLabel. Now will this still be possible - won't the pixmap get cut off or over extend past the label when drawing it...

                            J.Hilk 1 Reply Last reply Reply Quote 0
                            • mrjj
                              mrjj Lifetime Qt Champion last edited by mrjj

                              Hi
                              yes you can do it without wrapping in a class, even i must say its a bit nicer. ( the way @J.Hilk has shown)

                              int GetBarHeight(int MAX) {
                                return rand() % (MAX - 5) + 5;
                              }
                              
                              void MainWindow::on_pushButton_released() {
                              
                                int h = ui->label->height();
                                int w = ui->label->width();
                              
                                QPixmap pix(w, h);
                                QPainter paint(&pix);
                                pix.fill( Qt::white );
                                paint.setPen(QColor(0, 0, 0, 255));
                              
                              
                                int y = 0;
                                int x = 0;
                              
                                int bw = 10; // bar width
                                for (int barcount = 0; barcount < 12; ++barcount) {
                                  paint.setBrush(QColor(255 - x, 34 + x, 255, 255));
                                  paint.drawRect(x, h - GetBarHeight(h),  bw, h );
                                  x += bw + 4;
                                }
                                paint.end();
                                ui->label->setPixmap(pix);
                              }
                              
                              

                              alt text

                              test project
                              https://www.dropbox.com/s/qwde8lb0fkjrrh3/mycheapgraph.zip?dl=0

                              1 Reply Last reply Reply Quote 1
                              • J.Hilk
                                J.Hilk Moderators @R-P-H last edited by J.Hilk

                                @r-p-h

                                Sorry you're correct, I was confusing the two of you.

                                No worries 😉

                                Why does this need to be in a class format like how you showed ? Can I not directly paint the QLabel ?

                                no, painting on a QLabel can only be done inside the paintEvent function. To access that function subclassing is requiert

                                Also I usually resize the image to the size of the label before putting it in QLabel. Now will this still be possible - won't the pixmap get cut off or over extend past the label when drawing it...

                                in the example the pixmap actually get’s stretched. In the end you have full control over it. But IIRC you will never be able to paint outside a Qwidgets boundaries.

                                ———
                                That said, you can potentially use the QPainter on the QPixmap directly and draw the axis that way.

                                Edit: @mrjj beat me to it, with an actual example as well 😳

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

                                Qt Needs YOUR vote: https://bugreports.qt.io/browse/QTQAINFRA-4121


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

                                1 Reply Last reply Reply Quote 1
                                • R
                                  R-P-H last edited by

                                  Thanks @J-Hilk and @mrjj , I will give it a try and see how it goes. ;)

                                  1 Reply Last reply Reply Quote 0
                                  • mrjj
                                    mrjj Lifetime Qt Champion last edited by mrjj

                                    Hi
                                    Regarding the axis.
                                    One option is to simply draw them in inkscape and save as SVG.
                                    Then just paint the SVG on top of the image.
                                    That should be faster than draw the ticks and values by hand using painter.
                                    However, if axis values change or zoom is needed then its not good idea.

                                    R 1 Reply Last reply Reply Quote 0
                                    • R
                                      R-P-H @mrjj last edited by

                                      @mrjj said in Draw basic Axes on QPixmap ?:

                                      Hi
                                      Regarding the axis.
                                      One option is to simply draw them in inkscape and save as SVG.
                                      Then just paint the SVG on top of the image.
                                      That should be faster than draw the ticks and values by hand using painter.
                                      However, if axis values change or zoom is needed then its not good idea.

                                      Hi, the "plot/image" is not interactive. The axis values do change but only each time a user changes a setting. So the axis would have to somehow be made on the fly for each "session". During the "session" the axis remain the same though while the image does change ! So I'm not sure what's the most efficient way of doing it...

                                      mrjj 1 Reply Last reply Reply Quote 0
                                      • mrjj
                                        mrjj Lifetime Qt Champion @R-P-H last edited by

                                        @r-p-h
                                        Well if its very dynamic then hand painting them with painter should do it.
                                        Overlaying a svg with only part of the axis is likely more fiddle fiddle to place the values correctly
                                        so just drawing it should be the way to go.
                                        Do you have image of the needed axis?

                                        R 1 Reply Last reply Reply Quote 0
                                        • R
                                          R-P-H @mrjj last edited by

                                          @mrjj said in Draw basic Axes on QPixmap ?:

                                          @r-p-h
                                          Well if its very dynamic then hand painting them with painter should do it.
                                          Overlaying a svg with only part of the axis is likely more fiddle fiddle to place the values correctly
                                          so just drawing it should be the way to go.
                                          Do you have image of the needed axis?

                                          The image is live though so it's constantly being displayed in a loop, so I'm not sure if re-drawing the axes constantly is such a good idea.

                                          mrjj 1 Reply Last reply Reply Quote 0
                                          • mrjj
                                            mrjj Lifetime Qt Champion @R-P-H last edited by

                                            @r-p-h
                                            oh, well for that sort of overlay,
                                            you will need to draw the axis
                                            anytime the image changes regardlessly.

                                            R 1 Reply Last reply Reply Quote 0
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