Redrawing on Window Resizing

static LRESULT 
OnSize(HWND hwnd, int w, int h) 
{ 
    HRESULT       hRes; 
    DDSURFACEDESC ddsd; 
 
        // Nothing to do if we are suspended. 
 
    if (!fSuspended) 
    { 
        // Update the source and destination rectangles (used by the 
        // blit that shows the rendering in the client area). 
 
        rDstRect.right  = rDstRect.left + w; 
        rDstRect.bottom = rDstRect.top  + h; 
        rSrcRect.right  = w; 
        rSrcRect.bottom = h; 
 
        if (NULL != lpd3dDevice) 
        { 
            // Although we already have a device, we need to be sure it 
            // is big enough for the new window client size. 
 
            // Because the window in this sample has a fixed size, it 
            // should never be necessary to handle this case. This code 
            // will be useful when we make the application resizable. 
 
            ZeroMemory(&ddsd, sizeof(ddsd)); 
            ddsd.dwSize = sizeof(ddsd); 
            hRes = lpddDevice->lpVtbl->GetSurfaceDesc(lpddDevice, 
                &ddsd); 
            if (FAILED(hRes)) 
            { 
                FatalError(hwnd, IDS_ERRMSG_DEVICESIZE, hRes); 
                return 0L; 
            } 
 
            if ((w > (int)ddsd.dwWidth) || (h > (int)ddsd.dwHeight)) 
            { 
                // The device is too small. We need to shut it down 
                // and rebuild it. 
 
                // Execute buffers are bound to devices, so when 
                // we release the device we must release the execute 
                // buffer. 
 
                ReleaseScene(); 
                ReleaseDevice(); 
            } 
        } 
 
        if (NULL == lpd3dDevice) 
        { 
            // No Direct3D device yet. This is either because this is 
            // the first time through the loop or because we discarded 
            // the existing device because it was not big enough for the 
            // new window client size. 
 
            hRes = CreateDevice((DWORD)w, (DWORD)h); 
            if (FAILED(hRes)) 
            { 
                FatalError(hwnd, IDS_ERRMSG_CREATEDEVICE, hRes); 
                return 0L; 
            } 
            hRes = CreateScene(); 
            if (FAILED(hRes)) 
            { 
                FatalError(hwnd, IDS_ERRMSG_BUILDSCENE, hRes); 
                return 0L; 
            } 
        } 
 
        hRes = UpdateViewport(); 
        if (FAILED(hRes)) 
        { 
            FatalError(hwnd, IDS_ERRMSG_UPDATEVIEWPORT, hRes); 
            return 0L; 
        } 
 
        // Render at the new size and show the results in the window's 
        // client area. 
 
        hRes = DoFrame(); 
        if (FAILED(hRes)) 
        { 
            FatalError(hwnd, IDS_ERRMSG_RENDERSCENE, hRes); 
            return 0L; 
        } 
    } 
 
    return 0L; 
}