Animated objects in dialog application do not stay on a background

Hi, experts!

I am trying to build an animated object in my dialog application:

1. User clicks on button1 and object1(bitmap1) moves then draws into background a few times  at some point in dialog
2. User clicks on button2 and the object moves then draws into background  a few times at some other point in dialog.
In the code snippet bellow the drawings do not remain on dialog’s background.
All the object drawings must remain on dialog’s background and do not get erased after dialog is dragged off screen or other drawings took a place in the same application.

Working code sample is greatly appreciated!

Thank you for your help in advance

BOOL CFlickerFreeDlg::OnInitDialog()
{
	CDialog::OnInitDialog();

	BITMAP bm;
	CClientDC dc(this);

	m_picture.topleft.x = 0;m_picture.topleft.y = 0;
	m_offs.cx = 0;m_offs.cy = 0;

	m_CanvasDC->CreateCompatibleDC(&dc);
	m_PicDC->CreateCompatibleDC(&dc);
	m_FinalCanvasDC->CreateCompatibleDC(&dc);

	m_BkgBitmap->LoadBitmap(IDB_BG);
	m_BkgBitmap->GetBitmap(&bm);
	m_hBkg = bm.bmHeight;
	m_wBkg = bm.bmWidth;
	m_Bitmap->LoadBitmap(IDB_PIC);
	m_Bitmap->GetBitmap(&bm);
	m_picture.height = bm.bmHeight;
	m_picture.width = bm.bmWidth;

	return TRUE;  
}


void CFlickerFreeDlg::OnPaint()
{

	CPaintDC dc(this);
	OnDraw(&dc);
}

void CFlickerFreeDlg::OnDraw(CDC* pDC)
{
	
		CBitmap* pOldBmp1; 
		CBitmap* pOldBmp2; 

		CRect cr;

		//selects canvas 
		pOldBmp1 = m_CanvasDC->SelectObject(m_CanvasBitmap);

		//selects background, blits into canvas
		pOldBmp2 = m_PicDC->SelectObject(m_BkgBitmap);
		m_CanvasDC->BitBlt(0, 0, m_wBkg, m_hBkg, m_PicDC, 0, 0, SRCCOPY);

		//selects small pic, blits into canvas
		m_PicDC->SelectObject(m_Bitmap);
		m_CanvasDC->BitBlt(m_picture.topleft.x, 
			m_picture.topleft.y, 
			m_picture.width, 
			m_picture.height, 
			m_PicDC, 
			0, 0, SRCCOPY);

		//blits canvas on screen.The "dirty rectangle" part only.
		pDC->GetClipBox(cr);
		pDC->BitBlt(cr.left, cr.top, cr.right, cr.bottom, m_CanvasDC, cr.left, cr.top, SRCCOPY);

		//deselects all the bitmaps 
		m_CanvasDC->SelectObject(pOldBmp1);
		m_PicDC->SelectObject(pOldBmp2);


}

void CFlickerFreeDlg::OnSize(UINT nType, int cx, int cy) 
{
	ASSERT(!(m_CanvasBitmap == NULL));
	delete m_CanvasBitmap;
	m_CanvasBitmap = new CBitmap;
	CClientDC dc(this);
	m_CanvasBitmap->CreateCompatibleBitmap(&dc, cx, cy);

	CDialog::OnSize(nType, cx, cy);
}


BOOL CFlickerFreeDlg::OnEraseBkgnd(CDC* pDC) 
{
	return false;
}


CRect CFlickerFreeDlg::CalcDirtyRect(int pic_w, int pic_h, CPoint p1, CPoint p2)
{
	CSize PicSize(pic_w,pic_h);
	CRect r1(p1,PicSize);
	CRect r2(p2,PicSize);

	return r1 | r2;
}

void CFlickerFreeDlg::Animate(int count) 
{

	for (int i = 0; i < 40; i ++)
	{
	bAnimate = TRUE;

	CRect DirtyRc;
		DirtyRc.left = 0 + i*5;
		DirtyRc.right = DirtyRc.left + m_picture.width;
		DirtyRc.top = 0 + i*5;
		DirtyRc.bottom = DirtyRc.top + m_picture.height;

	m_picture.topleft.x = i*5;
	m_picture.topleft.y = i*5;

	if(i > (40 - count))
	{
	InvalidateRect(DirtyRc,1);
	}else if( i <= (40 - count) )
		{
		InvalidateRect(NULL,1);
		UpdateWindow();
		}

	bAnimate = FALSE;

	UpdateWindow();

	Sleep(100);
		
	}


}

void CFlickerFreeDlg::OnButton1() 
{
	Animate(9);
}


void CFlickerFreeDlg::OnButton2() 
{
	Animate(19);
}

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