Get the first/last visible line of a TRichEdit

Author: Thomas Stutz

function RE_GetLastVisibleLine(RichEdit: TRichEdit): Integer;

const

EM_EXLINEFROMCHAR = WM_USER + 54;

var

r: TRect;

i: Integer;

begin

{

The EM_GETRECT message retrieves the formatting rectangle

of an edit control.

}

RichEdit.Perform(EM_GETRECT, 0, Longint(@r));

r.Left := r.Left + 1;

r.Top := r.Bottom - 2;

{

The EM_CHARFROMPOS message retrieves information about the character

closest to a specified point in the client area of an edit control

}

i := RichEdit.Perform(EM_CHARFROMPOS, 0, Integer(@r.topleft));

{

The EM_EXLINEFROMCHAR message determines which

line contains the specified character in a rich edit control

}

Result := RichEdit.Perform(EM_EXLINEFROMCHAR, 0, i);

end;

{

Sending the EM_GETFIRSTVISIBLELINE message to a multi-line edit control

finds out which line is the first line visible.

This is the line that is currently displayed at the top of the control.

}

function RE_GetFirstVisibleLine(RichEdit: TRichEdit): Integer;

begin

Result := RichEdit.Perform(EM_GETFIRSTVISIBLELINE, 0, 0);

end;