The GET_Y_LPARAM macro retrieves the signed y-coordinate from the given LPARAM value.
int GET_Y_LPARAM(
LPARAM lParam // value from which the signed y-coordinate is retrieved
);
The return value is the high-order int of the specified value.
The GET_Y_LPARAM macro is defined as follows:
#define GET_Y_LPARAM(lp) ((int)(short)HIWORD(lp))
Windows Overview, Window Macros, GET_X_LPARAM, HIWORD, LOWORD