[FraKtus]

Maybe it is still VBL related, in the DX11 sample you will see this when presenting the final frame:

g_pSwapChain->Present(1, 0); // Present with vsync

//g_pSwapChain->Present(0, 0); // Present without vsync

So you can control this by setting the first argument to 1 or 0.

[Rusky]

It's not related. The "page tearing" problem is caused by the way imgui handles events.

You describe the UI by making a bunch of function calls, each of which immediately renders a piece of the UI and returns any relevant events (e.g. render a button, return whether it has been clicked). But this means that any event that should change how the UI is rendered may have missed its chance- what if the changed part of the UI has already had its function called that frame?

The "ideal" dataflow, as far as this problem is concerned, would be to fully process all the events in a frame (from raw input, to widget-level events like button presses, to application-specific stuff) before rendering anything.