@Dariusz As @mrjj said this is handled by the window manager. Dock widgets have the tool window style, which on Windows 10 means there is no distinctive line around the window, instead the actual resizing area on the left, right and bottom is the shadow, or more specifically about 2/3 of that shadow which is roughly 5 pixels wide (if you don't have any scaling enabled). That's actually quite enough and it's more than previous Windows versions used (I think XP used something like 2px wide border, although it was a solid line, not a shadow).
There are couple of ways to make that wider if you're really determined, but all of them require some work (IMO it's not worth it):
On detach change the window style to something with a more distinctive border (e.g. Qt::Window, although more visible border doesn't actually mean it's wider).
Give the dock some margin and handle the mouse event yourself to handle the resize inside the widget.
Use QtWinExtras::extendFrameIntoClientArea and handle native events to make the border wider. Note that also means you'd have to paint that border with native API i.e. GDI, as Qt can't paint on window frames..
This isn't directly supported, but you can achieve similar result if you make your central widget another QMainWindow. This has the downside that you can't move the toolbars between the two QMainWindows, unless you manage to reparent them dynamically while dragging (should be possible but I haven't tried it).
@ravas As the "docking animation" only shows up as soon as the mouse cursor (that currently drags a dockable widget) is inside the dockable area I assume that it is based on the cursor position and not the edge of the dockable widget.
Edit: Just figured that I might have given some wrong information. It looks like it just goes for the nearest dockable area when the dockable widget that is currently being dragged around is within a certain distance.
I know, and I want to, but I don't think I can because I can't create a good compilable example that reproduces the error. If you simply create a dockWidget that has a listView and you try to scroll it is fine. Even though I tried to configure it the same way.
I am not sure what exactly in my app triggered this bug.
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