GraphicsView: Implement pinch to zoom

[jeffwheeler]

This pull request is addresses #474.

The code in the initial pull request should not be merged, but is an initial example. I'd like to figure out how to make it work across platforms and with a mouse.

[jeffwheeler]

I have updated the pull request with a set of commits that I think should behave nicely for everyone.

I don't believe we need a preference setting to configure this. My intent is to leave mice behavior unchanged (including on Mac), but fix the currently broken trackpad behavior. I don't think anyone would want the existing trackpad behavior.

The commit fails CI on Ubuntu 14.04, I think because of an ancient version of Qt. Is that something you're interested in supporting? Canonical has dropped support for that platform already.

[ubruhin]

Thanks for the PR! :)

I found some issues and have some questions/suggestions, see comments below.

The commit fails CI on Ubuntu 14.04, I think because of an ancient version of Qt. Is that something you're interested in supporting? Canonical has dropped support for that platform already.

As long as it's easy, I'd like to keep support for Qt 5.2. So far it was always very easy to keep this support, so I saw no reason to drop it. One of LibrePCB's goals is the availability on many different systems (architectures, operating systems, distributions etc.). For example Debian oldstable still has Qt 5.3.2, and I don't like to drop support for a still supported distribution if not absolutely necessary.

[jeffwheeler]

Thanks for the feedback, I’ll review in a few days. :)

[rnestler]

For example Debian oldstable still has Qt 5.3.2, and I don't like to drop support for a still supported distribution if not absolutely necessary.

So we could bump the minimal required Qt version from 5.2 to 5.3

[jeffwheeler]

Hi @ubruhin, I think your comments should now be addressed. Behavior should be unchanged for old versions of Qt.

[ubruhin]

Thanks! Looks like you no longer use QNativeGestureEvent :)

Do I understand correctly that with this PR "pinch to zoom" works out-of-the-box on a MacBook?

I think there is still a small issue with the implementation: The method grabGesture() is called in setUseOpenGl(), but not in the constructor of GraphicsView. So by default, gestures are not grabbed and thus (probably) gestures won't work. But actually it still works "by accident" because setUseOpenGl() is called by users of GraphicsView anyway. If you want to fix this - perfect. If not - don't worry, I'd still merge this since it's not critical 🙂

Issues fixed.

[jeffwheeler]

Thanks! Looks like you no longer use QNativeGestureEvent :)

Yup. I discovered that QGestureManager::QGestureManager has an #if defined(Q_OS_OSX), and if so, registers the native Mac gesture recognizers (such as QMacPinchGestureRecognizer). Those gesture recognizers will trigger the standard gestures once they receive the native gestures.

Do I understand correctly that with this PR "pinch to zoom" works out-of-the-box on a MacBook?

Yup. 🙂

I think there is still a small issue with the implementation: The method grabGesture() is called in setUseOpenGl(), but not in the constructor of GraphicsView. So by default, gestures are not grabbed and thus (probably) gestures won't work. But actually it still works "by accident" because setUseOpenGl() is called by users of GraphicsView anyway. If you want to fix this - perfect. If not - don't worry, I'd still merge this since it's not critical 🙂

I'll push a fix for this momentarily.

[ubruhin]

Perfect, thank you very much for this improvement! 😃