An application sends an EM_GETFIRSTVISIBLELINE message to determine the uppermost visible line in an edit control.
EM_GETFIRSTVISIBLELINE wParam = 0; // not used; must be zero lParam = 0; // not used; must be zero
This message has no parameters.
The return value is the zero-based index of the uppermost visible line in a multiline edit control. For single-line edit controls, the return value is the zero-based index of the first visible character.