This message is sent when the size of a window's client area needs to be calculated.
wParam
This parameter is not used.
lParam
Points to an NCCALCSIZE_PARAMS data structure that contains information an application can use to calculate the new size and position of the client rectangle. The NCCALCSIZE_PARAMS structure has the following form:
typedef struct tagNCCALCSIZE_PARAMS {
RECT rgrc[3];
WINDOWPOS FAR* lppos;
} NCCALCSIZE_PARAMS;