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);

To copy to clipboard, switch view to plain text mode 

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.

[anda_skoa]

To rotate around a certain point you need to translate() into that point and then rotate()

Cheers,
_

[Andree]

so if i have a triangle which is used like a needle in analog gauge and i want rotate only end of needle, the beginning of the needle must be in this same position. so if i want rotate needle i must use this:

painter.translate(-80, 84);
painter.rotate(20);

painter.translate(-80, 84);
painter.rotate(20);

To copy to clipboard, switch view to plain text mode 

But then this triangle change his own position
It should look something like this, only end of needle change position
wgauge2.jpg