Resizing using window manager functionality (e.g. clicking and dragging
in the non-client area) will send WM_SIZING to the window, which in turn
will enable continuous repainting in the D2D renderer until the resize
operation ends.
Continuous repainting is required in order for the window to display
correctly during the resize. Without continuous repainting, some frames
may not be completely painted, and may display with black areas,
producing a flickery effect.
When a resize is controlled entirely by the client, e.g. using the
corner resizer in the AudioPluginDemo standalone, WM_SIZING is never
posted. Instead, we assume that if the window has captured the cursor
during a setBounds call then it is probably resizing. We enable
continuous repainting in this case, and stop repainting once the window
releases the mouse.
An alternative appropach would be to add some kind of start/stop resize
API to ComponentPeer. I'm currently reluctant to do that because the
ComponentPeer API is already so large.
