Delphi VCL Form background pattern

form pattern.pas

procedure TMainForm.paintBackground();
var
	bmp: TBitmap;
	rect: TRect;
	left, right: TRect;
begin
	bmp := TBitmap.Create();
	try
		// generate pattern
		bmp.SetSize(Image1.Picture.Width, Image1.Picture.Height);
		bmp.Transparent := False;

		rect := bmp.Canvas.ClipRect;
		left := rect.SplitRect(TSplitRectType.srLeft, xOffsetPx);
		right := rect;
		right.Offset(xOffsetPx, 0); right.Right := rect.Width;

		bmp.Canvas.Pen.Color := TColors.Blue;
		bmp.Canvas.Brush.Color := TColors.Blue;
		bmp.Canvas.FillRect(left);

		bmp.Canvas.Pen.Color := TColors.Red;
		bmp.Canvas.Brush.Color := TColors.Red;
		bmp.Canvas.FillRect(Right);

		// Clear form canvas
		Canvas.Pen.Color := Color;
		Canvas.Brush.Color := Color;
		Canvas.FillRect(Canvas.ClipRect);

		// paste pattern
		Canvas.Brush.Bitmap := bmp;
		Canvas.FloodFill(0, 0, Color, TFillStyle.fsBorder);
	finally
		bmp.Destroy();
	end;
end;