Author: Jonas Bilinkevicius

How to display text from a TRichEdit on the canvas of a TGraphicControl

Answer:

If you just want to view the text you can make a component derived from 
TGraphicControl. The following code shows how to put text from a TRichEdit control 
on the canvas of the TGraphicControl.
1   
2   {rtf is a property of the TRICHLABEL of the type TRichEdit }
3   
4   procedure TRICHLABEL.Paint;
5   var
6     myFormatRange: TFormatRange;
7     myCharRange: TCharRange;
8     myRect: TRect;
9     OldMap: Integer;
10    LastChar: Integer;
11    rc: TRect;
12    hDC, hDCTarget: THandle;
13  begin
14    if not Assigned(rtf) then
15      exit;
16    FillChar(myFormatRange, sizeof(TFormatRange), 0);
17    myCharRange.cpMin := 0;
18    myCharRange.cpMax := -1;
19    canvas.brush.color := BackColor;
20    if FTransparent then
21      Canvas.brush.style := bsClear
22    else
23    begin
24      Canvas.brush.style := bsSolid;
25      Canvas.FillRect(ClientRect);
26    end;
27    with myFormatRange do
28    begin
29      hDC := canvas.handle;
30      hDCTarget := canvas.handle;
31      rc := Rect(0, ptOrigin.y * 15, Width * 15, ptOrigin.y * 15 + Height * 15);
32      chrg.cpMin := 0;
33      chrg.cpMax := -1;
34    end;
35    LastChar := SendMessage(rtf.handle, EM_FORMATRANGE, 1, LPARAM(@myFormatRange));
36    myRect := Rect(0, 0, width * 15, height * 15);
37    SendMessage(rtf.handle, EM_DISPLAYBAND, 0, LPARAM(@myRect));
38    LastChar := SendMessage(rtf.handle, EM_FORMATRANGE, 0, LPARAM(nil));
39  end;