QGraphicsItem Opacity Mask

[sdanahy]

Does anyone know of a way to apply an opacity mask to a QGraphicsItem and it's children? Basically I'm looking to define per-pixel opacity like a bitmap's alpha channel. The feature looks like it will be available in Qt 4.6 via QGraphicsOpacityEffect, but I'm wondering if anyone knows of a solution for Qt 4.5.2.

Thanks!

Scott

[wysota]

If you mean an arbitrary item then I don't think it is possible. If you mean for your own items then by overriding mouse events and reimplementing the paint routine you should be able to do appropriate masking.

[scascio]

There is opacity features fo QGraphicsitem but with same opacity for all pixels. Not per-pixel defined.
You can can play with QGraphicsItem::opaqueArea to define a mask independtly of opacity.

I can't see any solution without overloading the paintEvent, draw into a QPixmap and defined you per-pixel opacity mask with alpha channel.

What is the goal of your need? Maybe another design cans take benefits of Qt features.

[sdanahy]

Thanks to both of you for the response.

All of the items in the view are mine, but the problem with just overriding the paint routine is that I want the mask to apply to the item's children as well (which are drawn after the item, if I understand correctly). I could propagate the opacity mask down the display tree, but then every item in my view would need a custom paint routine that would apply the mask. That seems awfully cumbersome so I was looking for a better way.

Thanks again for the ideas...

Scott