Ewkoll

First received WM_NCCALCSIZE message, If wParam is FALSE, lParam points to a RECT structure. null error

2

 https://docs.microsoft.com/en-us/windows/win32/winmsg/wm-nccalcsize If wParam is TRUE, lParam points to an [NCCALCSIZE_PARAMS](https://docs.microsoft.com/en-us/windows/win32/api/winuser/ns-winuser-nccalcsize_params) structure that contains information an application can use to calculate the new size and position of the client rectangle....