When there is a context with a surface current, keep on using
that whenever ensureContext() is called without specifying a
QWindow.
Consider the following sequence:
<component A>
beginOffscreenFrame
render to texture 1
endOffscreenFrame
<component B>
beginOffscreenFrame
render to texture 2
endOffscreenFrame
<component C>
beginFrame (with swapchain)
render something using texture 1 and 2
endFrame
repeat all over again, continuously
(in practice this is what a top level widget with QOpenGLWidgets
and/or QQuickWidgets in it would lead to with the QRhi migration
in place)
Besides being more readable, the new version recognizes that resource
and offscreen operations do not need one specific surface (like the
one QOffscreenSurface every GL backend of QRhi has), but are functional
with any surface (or with surfaceless even) as long as the context is
correct. Thus with the above example we can work with only ever making
the one QWindow current.
Change-Id: I633071cae88f02e1d45e445ee55c8a58f9ec5a8c
Pick-to: 6.2
Fixes: QTBUG-96405
Reviewed-by: Andy Nichols <andy.nichols@qt.io>
c1899ca310