也是看别人写的，但是不容易找到，就转发一篇delphi版本的

function GetLine(X, Y: integer): TPoint;
var
  OldFont : HFont;
  Hand : THandle;
  TM : TTextMetric;
  Rect : TRect;
begin
  Hand := GetDC(mmotest.Handle);
  try
    OldFont := SelectObject(Hand, mmotest.Font.Handle);
    try
      GetTextMetrics(Hand, TM);
      mmotest.Perform(EM_GETRECT, 0, longint(@Rect));
      Result.Y:= GetScrollPos( mmotest.Handle, SB_VERT ) +
                 (Y - Rect.Top) div (TM.tmHeight);
      Result.X:= (X - Rect.Left) div (TM.tmHeight);
      
      ShowMessage( IntToStr( Result.X ) + ',' + IntToStr( Result.Y ) );
    finally
      SelectObject(Hand, OldFont);
    end;
  finally
    ReleaseDC(mmotest.Handle, Hand);
  end;
end;

procedure TF_Main.mmotestMouseMove(Sender: TObject; Shift: TShiftState; X,
  Y: Integer);
begin
  GetLine( x, y );
end;

http://blog.csdn.net/youthon/article/details/5781995