Because DXGI flip mode swapchain will disallow GDI operation
to a HWND once swapchain is configured, videosink has been creating
child window of application's window. However, since window creation
would take a few milliseconds, it can cause performance issue such as
UI freezing. Adding a property so that videosink can attach
DXGI swapchain diretly to application's window in order to improve
performance.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/7013>
A large refactoring commit for adding features and improve performance
* Reuse internal converter and overlay compositor:
Converter can be reused as long as input and display formats are not
changed. Also overlay compositor reconstruction is required only if
display format is changed
* Don't wait for full GPU flush on resize or close:
D3D12 swapchain requires GPU idle in order to resize backbuffer.
Thus CPU side waiting is required for swapchain related commands
to be finished. However, don't need to wait for full GPU flushing.
* Support multiple sink on a single external window
Keep installed subclass window procedure even if there's no associated
our internal HWND. This will make window procedure hooking less racy.
Then parent HWND's message will be transferred to our internal HWNDs
if needed.
* Adding support for window handle update
Application can change target HWND even when videosink is playing or
paused state. So, users can call gst_video_overlay_set_window_handle()
against d3d12videosink anytime. The videosink will be able to update
internal state and setup resource upon requested.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/7013>
