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I would like to rotate a widget around its Y axis (or any axis) in QT exactly the same way as appearing here:

Image rotation in 3D space around Y axis

I have searched but all what I got 2d transformation like rotate clockwise or counterclockwise

I really want something very simple because I will do this once in the whole project.

Community
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Muhammad Nour
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3 Answers3

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Firstly, a normal Qt widget cannot do this because of the way the painting engine operates (it's entirely 2D), and the way the layout managers work, so any solution is non-trivial.

The simplest way to do it, is to put the widget into a QGraphicsScene/View as a QGraphicsProxyWidget, and use the setTransform(const QTransform&, bool) method to apply a transformation matrix.

However because the engine is still 2D, you will have to create a 3D transformation matrix describing the operation you want, then use projection to convert into a 2D matrix. It's not simple, but you can 'fake' the effect like the one you linked to by using the static method squareToQuad(const QPolygonF&, QTransform&) - as the user 'rotates' the widget one vertical edge becomes smaller and moves towards the quad centre, whilst the opposite edge becomes bigger and moves towards the quad centre.

cmannett85
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  • actually I am not that much expert in 3d programming, so I think try to fake it or try mimic it is much simpler for me – Muhammad Nour Jan 27 '13 at 10:44
  • You could subclass `QGraphicsProxyWidget` to provide custom properties for the transformations you are faking. Then you could use `QPropertyAnimation` to drive them. – cmannett85 Jan 27 '13 at 11:06
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Easiest to make and understand might be, paint the widget to a QPixmap. Then subclass QWidget wo paint this QPixmap transformed to match 3D rotation, or "fake" rotation. Since this painting is neatly inside single paintEvent() in your custom widget, it's easy to start with fake version (like, no perspective), then get back to it and improve it if there's time and need.

For example, it'd be quite easy to make painting use OpenGL, for example based on "Textures" example in openGL examples of Qt.

hyde
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    The only problem with doing the transformation within it's `paintEvent(..)` (which does have the advantage of not needing `QGraphicsView` to display it), is that you would also have to remap all the mouse interaction. – cmannett85 Jan 27 '13 at 10:51
  • Ah yes. I somehow assumed it's just an animation without simultaneous mouse interaction. Question does not specify, so this depends on that. – hyde Jan 27 '13 at 11:46
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If you really want to accomplish this in a Qt project in a way that would integrate well with other user interface widgets I would recommend checking out Qt Quick (Qt 4.7 +) or Qt Quick 2.0 (Qt 5.0 + ). They are intentionally designed to help facilitate the create of more dyanmic interfaces. They use QML (css-like markup language that describes widget functionality) coupled with a the familiar higher level C++ wrapper that can be accessed as any other Qt widget. Qt Quick 2.0 is especially cool, being able to draw cool particle system effects with relative ease.

Sir Digby Chicken Caesar
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