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TextEdit painting C++



  • Hi everyone,
    I read many posts of how to paint on Qtextedit, but I cannot get out of the problem.

    I create a form with a qtextedit named text and a class named textedit. Then, I wrote paintEvent(QPaintEvent* event) method in this way:

    void textedit::paintEvent(QPaintEvent* event)
    {
            QCursor cursorQ = ui->text->cursor();
            QPoint point= cursorQ.pos();
            QPainter p(this);
            p.drawText(QPoint(30,30), "|");
            p.drawText(point, "|");
    }
    

    The first drawText works and draw "|" character out of the QTextEdit area in the QPoint(30, 30), the second don't and I don't understand why.
    It's produced:
    "QWidget::paintEngine: Should no longer be called
    QPainter::begin: Paint device returned engine == 0, type: 1"
    output.
    Maybe it is because QPainter is reffered to the entire window and QPoint only to Qtextedit area? If this is the reason, how can I get what I want?
    I read some posts where people recommend using

    QPainter p(viewport());
    

    but it produced "used of undeclared identifier viewport " error.

    What can I have miss?

    (I used drawtext only as example for me, for understanding how to paint in the QTextEdit area)

    There .cpp and .h files:

    #ifndef TEXTEDIT_H
    #define TEXTEDIT_H
    
    #include <QMainWindow>
    #include <QCursor>
    #include <unistd.h>
    #include <QTextCharFormat>
    #include <QTextCursor>
    #include <QDebug>
    #include <QPainter>
    
    namespace Ui {
    class textedit;
    }
    
    class textedit : public QMainWindow
    {
        Q_OBJECT
    
    public:
        explicit textedit(QWidget *parent = nullptr);
        ~textedit();
    
    private:
        Ui::textedit *ui;
        QTextCursor cursor;
    
    protected:
        void paintEvent(QPaintEvent* event);
    };
    
    #endif // TEXTEDIT_H
    
    #include "textedit.h"
    #include "ui_textedit.h"
    
    textedit::textedit(QWidget *parent) :
        QMainWindow(parent),
        ui(new Ui::textedit)
    {
        ui->setupUi(this);
        ui->text->setText("Hello, World!\nAnotherLine.\n");
    
    }
    
    textedit::~textedit()
    {
        delete ui;
    }
    void textedit::paintEvent(QPaintEvent* event)
    {
            QCursor cursorQ = ui->text->cursor();
            QPoint point= cursorQ.pos();
            QPainter p(this);
            p.drawText(QPoint(30,30), "|");
            p.drawText(point, "|");
    }
    

    Thanks for any reply or advice.


  • Lifetime Qt Champion

    Hi,

    point is likely local to the QTextEdit so completely unrelated to your QMainWindow. You have to translate the coordinate to make it draw where you want.



  • @SGaist how can I do this? For what I need I have to start from the cursor position


  • Lifetime Qt Champion

    Take a look at the various point mapping related functions.



  • @SGaist Thank you!


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