I've just tried using the new RHI backend with a non-trivial application on macOS Metal. Very impressive!
However It looks like transparent toplevel windows are not yet supported. This also used to be a problem in QtQuick 2 early days (
The following example uses a transparent window background with QSG_RHI=0 but a black background with QSG_RHI=1.
Setting QQuickWindow::setDefaultAlphaBuffer(true) early in main.cpp does not make any difference.
|For Gerrit Dashboard: QTBUG-78089|
|273339,4||Request correct alpha composition on the rhi code path||5.14||qt/qtdeclarative||Status: MERGED||+2||0|
|273344,10||rhi: metal: Configure the layer's opaque property as appropriate||5.14||qt/qtbase||Status: MERGED||+2||0|
|273350,7||rhi: d3d11: Fix enabling alpha compositing||5.14||qt/qtbase||Status: MERGED||+2||0|