It's a minimal change, it just calls an already existing protected method. It was trivial to subclass the handler to do it in our code, but pushing the change into OSG makes sense as it's generally useful to have it in the handler itself.
I also noticed that the handle() method was overridden from osgGA::GUIEventHandler but wasn't marked virtual. It wasn't intended that subclasses not be able to override it in turn, so I've added the keyword.""
viewer.addEventHandler(new osgViewer::ScreenCaptureHandler(
new osgViewer::WriteToFileCaptureOperation("filename", "jpg")));
and the filename will be what you want. The WriteToFileCaptureOperation will add the context ID and the file number (if in SEQUENTIAL_NUMBER mode) to the file name.
(The attached also clarifies some notify messages, and corrects the comment when adding the handler in osgviewer.cpp)
I also remembered, the current architecture could allow a different CaptureOperation for each context, but currently the API only allows setting one CaptureOperation for all contexts. This could be improved if need be.
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