Rotate about point

[Andree]

Hello,

At first I would like to apologize you for my english.

I have a triangle, let's say like this

static const QPoint T[3] = {
        QPoint(80, 80),
        QPoint(80, 88),
        QPoint(-80, 84)
    };
painter.drawConvexPolygon(T, 3);

static const QPoint T[3] = {
        QPoint(80, 80),
        QPoint(80, 88),
        QPoint(-80, 84)
    };
painter.drawConvexPolygon(T, 3);

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and I want to rotate this triangle about point a(-80.0,84.0). HHow can I do this?
It will be in loop so i want to change only degrees. And when i want to change degrees it should be come back on the first position. Thanks for help.