rhi: Add the long-pending probe() helper, with backing for Metal

There is a TODO for this in Qt Quick from the 6.0 times. To decide
upfront if Metal can be expected to function, or if a fallback to
OpenGL needs to be triggered (especially important with macOS virtual
machines, where, unlike any real macOS system, Metal may not be
present at all), the scenegraph calls create() and then drops the
result. The idea to make this less wasteful was back then to add a
dedicated probing function which can, possibly, perform the checks in
a more lightweight manner than full initialization. Implement this
now, focusing on Metal.

Brought to attention by QTBUG-100441: printing warnings about not
having an MTLDevice is confusing in a Metal-less macOS VM, because it
is not an actual error, only part of the probing at scenegraph
initialization. We can now avoid printing confusing warnings there.

Change-Id: Ie52c36af9224bedc3f5e4c23edb486d961c9f216
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Andy Nichols <andy.nichols@qt.io>

1 files changed, 1 insertions, 0 deletions

diff --git a/src/gui/rhi/qrhi_p.h b/src/gui/rhi/qrhi_p.h
index 972aed6fd8..c96b773e0b 100644
--- a/src/gui/rhi/qrhi_p.h
+++ b/src/gui/rhi/qrhi_p.h
@@ -1711,6 +1711,7 @@ public:
                         QRhiInitParams *params,
                         Flags flags = {},
                         QRhiNativeHandles *importDevice = nullptr);
+    static bool probe(Implementation impl, QRhiInitParams *params);
 
     Implementation backend() const;
     const char *backendName() const;