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

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?