> Is that true? Handling WM_SIZING alone was not enough. No, simply handling WM_SIZING or WM_SIZE is not enough in the current scenario. There is a separate system message SC_SIZE under the WM_SYSCOMMAND (https://docs.microsoft.com/en-us/windows/win32/menurc/wm-syscommand) which is posted when the user tries to resize the window.
Currently the DefWindowProc handles the SC_SIZE command and it goes into a loop while the window is being resized. So, you need to handle this message and resize the window manually according to the mouse position. I'll try to implement this and let you know. Anuj
