I got a QWidget / QPainter font rendering problem on Windows 10 64 bit desktop using Qt 5.7.0.

Look the following screenshots. Using Qt the space between 'tt' and 'ti' is missing at Calibri and Carlito font:

Qt: https://s19.postimg.org/dzl1pst8z/image.png

Wordpad (Windows): https://s19.postimg.org/9rq9h1rtf/Wordpad_Windows.png

LibreOffice: https://s19.postimg.org/9t07agtn7/Libre_Office.png

Sourcecode of the Qt screenshot:

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

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

protected:
	void paintEvent(QPaintEvent *);
};

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

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

    painter.setRenderHints(QPainter::Antialiasing | QPainter::TextAntialiasing);

    QFont Calibri_18_Normal("Calibri", 22, QFont::Normal);
    QFont Calibri_18_Bold("Calibri", 22, QFont::Bold);
    QFont Arial_18_Normal("Arial", 22, QFont::Normal);
    QFont Arial_18_Bold("Arial", 22, QFont::Bold);
    QFont Carlito_18_Normal("Carlito", 22, QFont::Normal);
    QFont Carlito_18_Bold("Carlito", 22, QFont::Bold);

    int y = 100;

    painter.setFont(Calibri_18_Bold);
    painter.drawText(200, y += 40, "Qt: Look for missing space between 'tt' and 'ti'");

    painter.setFont(Calibri_18_Normal);
    painter.drawText(200, y += 80, "Calibri: Rating Betting Setup - (Windows Clear Type)");
    painter.setFont(Calibri_18_Bold);
    painter.drawText(200, y += 40, "Calibri: Rating Betting Setup - (Windows Clear Type)");

    painter.setFont(Arial_18_Normal);
    painter.drawText(200, y += 80, "Arial: Rating Betting Setup - (Windows)");
    painter.setFont(Arial_18_Bold);
    painter.drawText(200, y += 40, "Arial: Rating Betting Setup - (Windows)");

    painter.setFont(Carlito_18_Normal);
    painter.drawText(200, y += 80, "Carlito: Rating Betting Setup - (Open Source, LibreOffice)");
    painter.setFont(Carlito_18_Bold);
    painter.drawText(200, y += 40, "Carlito: Rating Betting Setup - (Open Source, LibreOffice)");
}

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