Draw shape with Qt pushbutton

[Moon4Walker]

First of all, I'm new to qt.
I have a program that reads data from a file and draws a shape using qpaintevent. My question is, I want my function that draws a shape to be active when I press the button using a pushbutton u signal slot.

void MainWindow::paintEvent(QPaintEvent *event)
{
    int w = width(), h= height();
    int xx1= w/2;
    int yy1= h/2;
    int xx2= w/2;
    int yy2= h/2;

    QFile file("C:/Users/Osman/Desktop/emir_kodlari.txt"); //UPDATE!

    if(!file.open(QFile::ReadOnly | QFile::Text)){
        QMessageBox::warning(this,"Error", "File not open");
    }

    QTextStream in(&file);

        rotate=0;

        QPainter painter(this) ;
        painter.setPen(QPen(Qt::black,7)); //set the color and width of line.

        while (!in.atEnd()) {

            QString line = in.readLine().trimmed();

           if(line.mid(0,1) == "f"){

             number= ((line.mid(1, line.length())).trimmed()).toInt();

             // Create the line object
             QLineF* angleLine= new QLineF();

             // Set the first point
             angleLine->setP1(QPointF(xx1,yy1).toPoint());

             angleLine->setAngle(rotate);
             angleLine->setLength(number);

             // Draw the line
             painter.drawLine( angleLine->toLine() );

             xx1 = angleLine->x2();
             yy1 = angleLine->y2();

             //qDebug()<< "number:" << number;

            }

          else if(line.mid(0,1) == "r"){

               rotate += ((line.mid(1, line.length())).trimmed()).toInt();
              // qDebug()<< "rotate:" << rotate;
           }
           else if(line=="RESET"){ //after loop-> L 4[F 100 R 90] R10
               xx1=xx2;
               yy1=yy2;
           }

            else{
                qDebug()<< "empty line...";
            }

        }
        file.close();

}

[JonB]

@Moon4Walker said in Draw shape with Qt pushbutton:

I have a program that reads data from a file and draws a shape using qpaintevent.

You certainly do not want your code inside a paintEvent()!

I would suggest you put a QGraphicsView on your MainWindow and use QGraphicsScene to do your drawing work.

[Moon4Walker]

@JonB so can i know the reason for this?

[mrjj]

@Moon4Walker
Hi
When used in paint event, it will read the same file over and over. paintEvent is called pretty often and it's simply not
a good design to do all every time it redraws.

So It's better to split into a read data in function and one that draws the same. (could be paint event)

[Moon4Walker]

@mrjj I did not fully understand what you are saying. Sorry for my bad English.

[SGaist]

Hi,

What @mrjj suggests is to load the data only once and then reuse it in your paintEvent.

Since the data does not change. Just read the file in your class constructor.