Give Your Forms a Background

Problem/Question/Abstract:

Web pages use tiled bitmaps to create backgrounds. Is it possible to do this in Delphi?

Answer:

Before I learned how to do this, to create a background on a form, I'd drop a TImage on my form, then set its Align property to alClient. For low-resolution bitmaps, the pixelation that would occur at times was absolutely terrible! But with the method that I'll show you here (Note: this is merely ONE way of doing it), you can easily tile bitmaps on the surface of your form. The trick is in trapping the WM_ERASEBKGND message in a handler, creating a bitmap at runtime, then writing a quick bit of code in the OnPaint event handler. Let's go through the steps.

1. In the private section of your code place the following:

private
{ Private declarations }
MyBitmap: TBitmap;

procedure WMEraseBkgnd(var m: TWMEraseBkgnd);
�� message WM_ERASEBKGND;

Notice the declaration of MyBitmap. We'll be creating an instance for it below. The message handler for WM_ERASEBKGND looks like this:

procedure TBmpform.WMEraseBkgnd(var m: TWMEraseBkgnd);
begin
  � m.Result := LRESULT(False);
end;

2. Then, create the following code for the OnPaint event handler Note: In the original article, the "x := x + MyBitmap.Width" is a bit inefficient in that continuously accessing the Bitmap.Width or .Height properties can slow things down - especially when you've got code in the OnPaint method. So what I did here was to simply set a couple of variables to store the Width and Height property values of the bitmap.

procedure TBmpForm.FormPaint(Sender: TObject);
var
  x, y: Integer;
  iBMWid, iBMHeight: Integer;
begin
  iBMWid := MyBitmap.Width;
  iBMHeight := MyBitmap.Height;
  y := 0;
  while y < Height do
  begin
    x := 0;
    while x < Width do
    begin
      Canvas.Draw(x, y, MyBitmap);
      x := x + iBMWid;
    end;
    y := y + iBMHeight;
  end;
end;

3. Finally, create an instance of the bitmap you want to tile in the background in the OnCreate event of your form:

procedure TForm1.FormCreate(Sender: TObject);
begin
  Application.OnHint := ShowHint;
  MyBitmap := TBitmap.Create;
  MyBitmap.LoadFromFile('Brick4.bmp');
end;

4. Whoops, almost forgot! You need to destroy the bitmap when you exit!

procedure TForm1.FormClose(Sender: TObject; var Action: TCloseAction);
begin
  Action := caFree;
  bmpBackground.Free;
end;

Well, that's it. Don't you just love the quick and dirty ones?