Drawing lines in QPainter takes a lot of time

[Lesiok]

Maybe I repeat myself but... This is the original code :

const int cst_nbLines = 5000;
 
    for (int i=0 ; i<cst_nbLines ; i++)
    {
        QLine myLine(i/10, i/10, i/10+300, i/10);
        myPainter.drawLine(myLine);
    }

const int cst_nbLines = 5000;

    for (int i=0 ; i<cst_nbLines ; i++)
    {
        QLine myLine(i/10, i/10, i/10+300, i/10);
        myPainter.drawLine(myLine);
    }

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This is the code giving the same final result but 10 times faster :

const int cst_nbLines = 5000;
 
    for (int i=0 ; i<cst_nbLines/10 ; i++)
    {
        QLine myLine(i, i, i+300, i);
        myPainter.drawLine(myLine);
    }

const int cst_nbLines = 5000;

    for (int i=0 ; i<cst_nbLines/10 ; i++)
    {
        QLine myLine(i, i, i+300, i);
        myPainter.drawLine(myLine);
    }

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