QGLWidget :: renderText（）创建一些向下移位的字母

Question

I created a class derived from QGLWidget:

class OpenGLWidget : public QGLWidget

I want to write some text on top of the OpenGL widget. Therefore I used the renderText() method inside the paintGL() of my class:

QString s = QString("AaBbCcDd");
renderText(10, 20, s);        // picture line 1

In the created text on top of my widget some letters are shifted downwards / upwards.

Have a look at this picture .

For example in the first line of the picture 'C', 'G', 'O' are shifted upwards and '4', '5' are shifted downwards.

I tried to change the font and the font size, but this only changed the letters, which are shifted, not the problem itself:

QFont font = QFont("Arial");
font.setPointSize(18);
renderText(10, 50, s, font);    // picture line 2

font = QFont("Times");
font.setPointSize(18);
renderText(10, 80, s, font);    // picture line 3

font = QFont("Courier");
font.setPointSize(18);
renderText(10, 110, s, font);   // picture line 4

font = QFont("Courier");
font.setPointSize(16);
renderText(10, 140, s, font);   // picture line 5

Does anybody know how to bring the letters on a straight line?

I also tried the QPainter::drawText() method instead of the renderText() inside the paintGL() of my class:

QPainter painter(this);
QString s = QString("AaBbCcDd");
painter.drawText(10, 20, s);

This method causes the same problem.

I am using Qt 4.7.4 with Qt Creator 2.4.1 on Mac OS 10.7.

Answer 1

This is a known bug in Qt 4.8.x. It affects Mac Qt-based applications that are run under OS X 10.7 and 10.8 (Lion and Mountain Lion). If you run your application under OS X 10.6 (Snow Leopard) you will not see the problem.

Qt 5.0.x fixes the renderText() problem for OS X 10.7 and 10.8 but is still too flaky to be used as a substitute for the more-solid 4.8.x builds.

Sadly, the Qt gods have not (yet) taken it upon themselves to retrofit the 4.8.x build with the fix from the 5.0.x build.