Running the BenchmarkDemoQt6 application features a massive
startup time, followed by running out of memory (GPU-side,
assuming a discreet adapter), which is then remedied by the
system with heavy swapping. This is due to creating 8+ GB
of staging data.
While there are doubts about the application itself (seems there
is an upload for each Quick 3D Texture per material per model,
even though the texture itself is the same?), there is no reason
for the D3D12 backend to use so much more memory compared with
other backends.
That is now ensured by only creating a staging area for the data
(taking the 256-aligned row pitch requirement into account), not
simply using the subresource (i.e. the whole image) size. This is
equivalent to what e.g. the Vulkan backend does.
Pick-to: 6.6
Fixes: QTBUG-116729
Change-Id: I1b5083c6b859ec0736cd9fd792cba8236aeba6e3
Reviewed-by: Andy Nichols <andy.nichols@qt.io>
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