Author: Maarten de Haan

How to draw a line in a RichEdit (just like in the Delphi editor)

Answer:

procedure DrawLine;

1   var
2     aCanvas: Tcanvas;
3     X1, X2, Y1: Integer;
4     byLineLength: BYTE;
5   
6   begin
7     byLineLength := 80; // Draw the line after 80 chars on the RichEdit
8     aCanvas := TCanvas.Create;
9     Y1 := RichEdit1.Height;
10    try
11      aCanvas.Handle := GetDC(RichEdit1.Handle);
12      aCanvas.Font := RichEdit1.Font;
13      X1 := aCanvas.TextWidth('W');
14      X2 := aCanvas.TextWidth('i');
15      aCanvas.Pen.color := clSilver; // Color of line
16      if X1 = X2 then // Check for fixed or variable font
17      begin
18        aCanvas.MoveTo(byLineLength * X1, 0);
19        aCanvas.LineTo(byLineLength * X1, Y1);
20      end;
21    finally
22      ReleaseDC(RichEdit1.Handle, aCanvas.Handle);
23      aCanvas.Free;
24    end;
25  end;