I've built my application (projected map) with the version 2.9 of osgEarth, and still have issues with REX engine.
1. REX engine is much slower than MP engine.
2. When using osgviewerMFC (OSG example based on MainFrame / ChildView), the view appears completely black. This is not the case when using MP engine (same code, options, resources, except the terrain engine).
3. When using osgViewer::setUpViewInWindow(), the terrain is well displayed but only the first time. If osgViewer is called twice, the terrain is not displayed anymore the second time. This is not the case when using MP engine (same code, options, resources, except the terrain engine).
Hi, I have the same problems with REX and QT, always the black screen. But, this can be solved by adding viewer.realize() after viewer.setSceneData . I think that this will resolve your problem with MFC.
Others problems appear after getting the viewer in the window, as aspect ratio, wrong position, some parts still in black, ....!!!!
For persons like me, that use osgEarth in another GUI (as Qt, MFC), the REX engine is still far from the MP engine. Many things as you mentioned don't work as expected.
I hope that these issues will be corrected so we can use the new features in REX because as gwaldron has explained "The MP terrain engine will remain, but we don't anticipate any further development".