Different paperSize of QPrinter on Windows and Mac

[ChrisW67]

I guess that if you look at the painter.device().logicalDpiX() and physicalDpiX() (or the Y equivalents) on the two platforms you'll find they are different. They possibly even change from printer to printer on the same platform. By default there's a 1:1 mapping from logical to physical.

If you are relying on the same numbers giving the same physical location on a page regardless of the underlying paint device then you'll need to look at setting a transformation to ensure that your logical coordinate system is what you expect. I have tended to set a transform to allow positioning in millimetres, but you might choose points, inches, light-seconds etc

Of course, I could be talking rubbish...I'm new to Qt

[cevou]

Can you give an example for that?

[ChrisW67]

Sorry, missed your request... it's something like:

// Set world coordinates to millimetres.
QTransform t = QTransform::fromScale (
    painter->device()->physicalDpiX() / 25.4,
    painter->device()->physicalDpiY() / 25.4 );
painter->setWorldTransform(t, false);

// Set world coordinates to millimetres.
QTransform t = QTransform::fromScale (
    painter->device()->physicalDpiX() / 25.4,
    painter->device()->physicalDpiY() / 25.4 );
painter->setWorldTransform(t, false);

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or you could just play with the painter window:

// For portrait A4 paper in millimetres
painter->setWindow(0, 0, 210, 297);

// For portrait A4 paper in millimetres
painter->setWindow(0, 0, 210, 297);

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You need to be careful because the transforms will scale everything. You can also use the QTransform without changing the painter.