I need some advice from a Qt expert.

The background: I have a 3D engine (ogre3d) working in concert with Qt. The 3D Content is displayed in a widget (using a custom OS window in the client area). I'm able to overlay arbitrary Qt widgets onto the 3d world using the widget render() method and a shared bitmap. This makes a great "heads up display". I can use the standard Qt style sheets and animation using this technique.

My goal I'd like to go a step further and allow the user to move these rendered widgets using the mouse. I'd like some advice on the best way to implement this.

Possible solutions:

  • The widgets in the HUD are not part of the inheritance chain. I render them manually. They don't get events though. I could add them to the inheritance chain so they get events in the usual way. Then I would need to change them to render to my shared bitmap instead of to the operating system. I looked at this once but couldn't find enough information to implement it.
  • Capture mouse events in the 3D display widget and EMIT them to child controls. I basically create my own event handling chain.

Any suggestions on how to implement this?

I'm also considering switching to Qt5. I'm not sure how that might affect this decision.


1 Answer 1


So far both solutions seem ok and none of them present any major drawback.

I guess the solution is the one you implent the quickest .

Now ...

if you choose a)

  • You need to create a render target

  • Push this as the current render target

  • draw your hud in this render target

  • pop it leaving you ogre window as the main render target

  • draw everything else here

then ..and this is the tricky part


  • get the pixels from the render target create a qimage and draw it


  • create a custom material that uses for the texture you render target's color buffer and draw a full screen quad with this material

in any case you should check tutorials 1 , 2 , 3

If you choose b)

you already figured out what to do ....

in your mouse mousePress , Released , Moved events from your qtglwindow just emit some events and whatever widgets is active or intersecting the mouse should respond to the event .

  • \$\begingroup\$ I implemented the hud by doing an Ogre overlay. I found a format of bitmap that the Qt QPainter and Ogre would both accept. I use that bitmap in a material in the Ogre overlay. For each frame that needs an update I clear the bitmap, call render() on each of the Qt widgets passing them the bitmap. Works very nicely. You get the style sheets and animation as well. \$\endgroup\$
    – Jay
    Dec 25, 2012 at 4:34
  • \$\begingroup\$ If I choose option A I need to implement the Qt render target, not the ogre render target. If I choose B I need mouse clicks and whatever is needed for Qt uses to track the mouse. I'd like the hover stylesheet options to work. Any idea how hover works? I may have to break down and start going through the Qt source code. \$\endgroup\$
    – Jay
    Dec 25, 2012 at 4:40
  • \$\begingroup\$ There is no qt Render target .. a render target is just and abstract notion in order to have the same operations if you render to a screen or to a texture(bitmap is such an old fashion way of putting it). Basically is exactly what you said you did in the first comment . Now if you choose b) check out qtgraphics scene event propagation doc.qt.digia.com/qt/… \$\endgroup\$ Dec 26, 2012 at 12:28
  • \$\begingroup\$ Sorry, I should have said "QPaintDevice" instead of Qt Render Target. I'll have a look at that link. Thanks :) \$\endgroup\$
    – Jay
    Dec 26, 2012 at 16:26

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