Direct3D11 objects are COM, and most COM C APIs are verbose
(C++ is a little better). So, by using C++ APIs, we can make code
shorter and more readable.
Moreover, "ComPtr" helper class (which is C++ only) can be
utilized, that is very helpful for avoiding error-prone COM refcounting
issue/leak.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/2077>
Since our decoder DPB texture pool cannot be grown once it's
configured, we should pre-allocate sufficient number of textures
for zero-copy playback (but not too many).
The "min buffers" allocation query parameter can be a hint for
the number of required textures in addition to DPB size.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/2017>
Unlike other stateless decoder implementations (e.g., VA),
our DPB pool cannot be grown since we are using
texture array (pre-allocated, fixed-size d3d11 texture pool).
So, if there's no more available texture to use,
there's no way other than copying it to downstream's
d3d11 buffer pool. Otherwise deadlock will happen.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/2003>
