Slow Graphics since Qt 5.6.0

[mireiner]

Hi wysota,

I found the bug. It's in QPainter:drawText() but only in combination with QPainter::setFont(). The following code runs two tests. A Windows 10 desktop application build with Qt 5.4.2, Qt 5.5.0 and Qt 5.5.1 will execute both tests with the same speed in debug mode. But build with Qt 5.6.0, Qt 5.6.1 or Qt 5.7.0 Test2 takes about 9 times longer than Test1!

#include <QApplication>
#include <QWidget>
#include <QPainter>
#include <QElapsedTimer>
 
class Widget : public QWidget
{
public:
    Widget();
 
protected:
    void timerEvent(QTimerEvent*);
    void paintEvent(QPaintEvent*);
 
private:
    QElapsedTimer elapsedTimer;
    int timerId;
    int elapsedTime1, elapsedTime2;
    bool isFinished1, isFinished2, isFinished3;
    int i, x1, x2, y1, y2;
};
 
Widget::Widget()
{
    setAutoFillBackground(true);
    setPalette(Qt::white);
 
    timerId = startTimer(1);
    elapsedTimer.start();
 
    i=0; x1=0; x2=0;
    isFinished1 = isFinished2 = isFinished3 = false;
}
 
void Widget::timerEvent(QTimerEvent*)
{
    update();
}
 
void Widget::paintEvent(QPaintEvent*)
{
    QPainter painter(this);
 
    if (i > 0 && i < 800)
    {
        // 'Test1' runs about 9 times faster than 'Test2' on Qt 5.6.0, Qt 5.6.1 and Qt 5.7.0
 
	y1 = 10;
	painter.setFont(QFont("Arial", 14));
	painter.drawText(x1, y1 += 30, "Test 1");
	painter.drawText(x1, y1 += 30, "row 01");
	painter.drawText(x1, y1 += 30, "row 02");
	painter.drawText(x1, y1 += 30, "row 03");
	painter.drawText(x1, y1 += 30, "row 04");
	painter.drawText(x1, y1 += 30, "row 05");
	painter.drawText(x1, y1 += 30, "row 06");
	painter.drawText(x1, y1 += 30, "row 07");
	painter.drawText(x1, y1 += 30, "row 08");
	painter.drawText(x1, y1 += 30, "row 09");
	painter.drawText(x1, y1 += 30, "row 10");
	painter.drawText(x1, y1 += 30, "row 11");
	painter.drawText(x1, y1 += 30, "row 12");
	x1++;
 
	elapsedTime1 = elapsedTimer.elapsed();
    }
    else if (i > 800 && i < 1600)
    {
        // 'Test2' takes about 9 times longer than 'Test1' on Qt 5.6.0, Qt 5.6.1 and Qt 5.7.0
 
	isFinished1 = true;
 
	y2 = 300;
	painter.setFont(QFont("Arial", 14));
	painter.drawText(x2, y2 += 30, "Test 2");
	painter.setFont(QFont("Caladea", 14));
	painter.drawText(x2, y2 += 30, "row 01");
	painter.setFont(QFont("Tomaha", 14));
	painter.drawText(x2, y2 += 30, "row 02");
	painter.setFont(QFont("Consolas", 14));
	painter.drawText(x2, y2 += 30, "row 03");
	painter.setFont(QFont("Calibri", 14));
	painter.drawText(x2, y2 += 30, "row 04");
	painter.setFont(QFont("Impact", 14));
	painter.drawText(x2, y2 += 30, "row 05");
	painter.setFont(QFont("Courier New", 14));
	painter.drawText(x2, y2 += 30, "row 06");
	painter.setFont(QFont("Gorgia", 14));
	painter.drawText(x2, y2 += 30, "row 07");
	painter.setFont(QFont("Verdana", 14));
	painter.drawText(x2, y2 += 30, "row 08");
	painter.setFont(QFont("Times New Roman", 14));
	painter.drawText(x2, y2 += 30, "row 09");
	painter.setFont(QFont("Microsoft Sans Serif", 14));
	painter.drawText(x2, y2 += 30, "row 10");
	painter.setFont(QFont("Segoe UI", 14));
	painter.drawText(x2, y2 += 30, "row 11");
	painter.setFont(QFont("Trebuchet MS", 14));
	painter.drawText(x2, y2 += 30, "row 12");
	x2++;
 
	elapsedTime2 = elapsedTimer.elapsed();
    }
    else if (i > 1600)
    {
	isFinished2 = true;
    }
    i++;
 
    if (isFinished1)
    {
	painter.setFont(QFont("Arial", 12, QFont::Bold));
	painter.drawText(QPoint(200, 150), "'Test1' elapsed time in seconds: " + QString::number(elapsedTime1/1000.0));
    }
    if (isFinished2)
    {
        painter.drawText(QPoint(200, 430), "'Test2' elapsed time in seconds: " + QString::number((elapsedTime2-elapsedTime1)/1000.0));
	isFinished3 = true;
    }
    if (isFinished3)
    {
        painter.setFont(QFont("Arial", 11));
        painter.drawText(QPoint(200, 620), "On Windows Desktop with Qt 5.4.2, Qt 5.5.0 and Qt 5.5.1 Test1 and Test2 are both equally fast.");
        painter.drawText(QPoint(200, 650), "On Windows Desktop with Qt 5.6.0, Qt 5.6.1 and Qt 5.7.0 Test2 is approx 9 times slower than Test1 !");
        painter.drawText(QPoint(200, 680), "No matter if compiled with MinGW 32bit or MSVC 32 or 64bit");
        killTimer(timerId);
    }
}
 
int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    Widget widget;
    widget.showMaximized();
    return app.exec();
}

#include <QApplication>
#include <QWidget>
#include <QPainter>
#include <QElapsedTimer>

class Widget : public QWidget
{
public:
    Widget();

protected:
    void timerEvent(QTimerEvent*);
    void paintEvent(QPaintEvent*);

private:
    QElapsedTimer elapsedTimer;
    int timerId;
    int elapsedTime1, elapsedTime2;
    bool isFinished1, isFinished2, isFinished3;
    int i, x1, x2, y1, y2;
};

Widget::Widget()
{
    setAutoFillBackground(true);
    setPalette(Qt::white);

    timerId = startTimer(1);
    elapsedTimer.start();

    i=0; x1=0; x2=0;
    isFinished1 = isFinished2 = isFinished3 = false;
}

void Widget::timerEvent(QTimerEvent*)
{
    update();
}

void Widget::paintEvent(QPaintEvent*)
{
    QPainter painter(this);

    if (i > 0 && i < 800)
    {
        // 'Test1' runs about 9 times faster than 'Test2' on Qt 5.6.0, Qt 5.6.1 and Qt 5.7.0

	y1 = 10;
	painter.setFont(QFont("Arial", 14));
	painter.drawText(x1, y1 += 30, "Test 1");
	painter.drawText(x1, y1 += 30, "row 01");
	painter.drawText(x1, y1 += 30, "row 02");
	painter.drawText(x1, y1 += 30, "row 03");
	painter.drawText(x1, y1 += 30, "row 04");
	painter.drawText(x1, y1 += 30, "row 05");
	painter.drawText(x1, y1 += 30, "row 06");
	painter.drawText(x1, y1 += 30, "row 07");
	painter.drawText(x1, y1 += 30, "row 08");
	painter.drawText(x1, y1 += 30, "row 09");
	painter.drawText(x1, y1 += 30, "row 10");
	painter.drawText(x1, y1 += 30, "row 11");
	painter.drawText(x1, y1 += 30, "row 12");
	x1++;
		
	elapsedTime1 = elapsedTimer.elapsed();
    }
    else if (i > 800 && i < 1600)
    {
        // 'Test2' takes about 9 times longer than 'Test1' on Qt 5.6.0, Qt 5.6.1 and Qt 5.7.0

	isFinished1 = true;

	y2 = 300;
	painter.setFont(QFont("Arial", 14));
	painter.drawText(x2, y2 += 30, "Test 2");
	painter.setFont(QFont("Caladea", 14));
	painter.drawText(x2, y2 += 30, "row 01");
	painter.setFont(QFont("Tomaha", 14));
	painter.drawText(x2, y2 += 30, "row 02");
	painter.setFont(QFont("Consolas", 14));
	painter.drawText(x2, y2 += 30, "row 03");
	painter.setFont(QFont("Calibri", 14));
	painter.drawText(x2, y2 += 30, "row 04");
	painter.setFont(QFont("Impact", 14));
	painter.drawText(x2, y2 += 30, "row 05");
	painter.setFont(QFont("Courier New", 14));
	painter.drawText(x2, y2 += 30, "row 06");
	painter.setFont(QFont("Gorgia", 14));
	painter.drawText(x2, y2 += 30, "row 07");
	painter.setFont(QFont("Verdana", 14));
	painter.drawText(x2, y2 += 30, "row 08");
	painter.setFont(QFont("Times New Roman", 14));
	painter.drawText(x2, y2 += 30, "row 09");
	painter.setFont(QFont("Microsoft Sans Serif", 14));
	painter.drawText(x2, y2 += 30, "row 10");
	painter.setFont(QFont("Segoe UI", 14));
	painter.drawText(x2, y2 += 30, "row 11");
	painter.setFont(QFont("Trebuchet MS", 14));
	painter.drawText(x2, y2 += 30, "row 12");
	x2++;

	elapsedTime2 = elapsedTimer.elapsed();
    }
    else if (i > 1600)
    {
	isFinished2 = true;
    }
    i++;
	
    if (isFinished1)
    {
	painter.setFont(QFont("Arial", 12, QFont::Bold));
	painter.drawText(QPoint(200, 150), "'Test1' elapsed time in seconds: " + QString::number(elapsedTime1/1000.0));
    }
    if (isFinished2)
    {
        painter.drawText(QPoint(200, 430), "'Test2' elapsed time in seconds: " + QString::number((elapsedTime2-elapsedTime1)/1000.0));
	isFinished3 = true;
    }
    if (isFinished3)
    {
        painter.setFont(QFont("Arial", 11));
        painter.drawText(QPoint(200, 620), "On Windows Desktop with Qt 5.4.2, Qt 5.5.0 and Qt 5.5.1 Test1 and Test2 are both equally fast.");
        painter.drawText(QPoint(200, 650), "On Windows Desktop with Qt 5.6.0, Qt 5.6.1 and Qt 5.7.0 Test2 is approx 9 times slower than Test1 !");
        painter.drawText(QPoint(200, 680), "No matter if compiled with MinGW 32bit or MSVC 32 or 64bit");
        killTimer(timerId);
    }
}

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    Widget widget;
    widget.showMaximized();
    return app.exec();
}

To copy to clipboard, switch view to plain text mode 

Did you know how to report a bug report to the Qt developer team? Never did that before. Can you help me with this?