A new feature enabled by Desktop Window Manager (DWM) is thumbnails of application windows.
However, DWM thumbnails are not static snapshots of a window.
They are dynamic, constant connections, between a thumbnail source window and a location on a destination window that receives the live thumbnail rendering.
This allows a quick view of applications by hovering over the application on the tool bar or using the ALT-TAB key gesture to see and quickly switch to the applications.
The following image illustrates the Windows Vista live thumbnails when you hover over the application on the tool bar.
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The following image illustrates the Windows Vista Flip (ALT-TAB) enabled by DWM.
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Note DWM thumbnails do not enable developers to create applications like the Windows Vista Flip3D (WINKEY-TAB) feature.
Thumbnails are rendered directly to the destination window in 2-D
This topic contains the following sections:
DWM Thumbnail Relationships
To display thumbnails in your application, you must first establish a relationship between a source HWND and a destination HWND.
This is done using the DwmRegisterThumbnail function.
DwmRegisterThumbnail does not render a thumbnail on the destination window but merely creates the relationship and provides the thumbnail handle.
The thumbnail is rendered once the DWM_THUMBNAIL_PROPERTIES have been set and DwmUpdateThumbnailProperties has been called.
Subsequent calls to DwmUpdateThumbnailProperties will update the thumbnail with a new set of properties.
The DWM also provides the helper function DwmQueryThumbnailSourceSize to determine the source window size from a thumbnail to help decide on proper thumbnail properties.
To end a thumbnail relationship, call DwmUnregisterThumbnail.
The following example demonstrates how to create a releationship with the desktop and display it in an application.
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HRESULT hr = S_OK;
//Register Thumbnail
HTHUMBNAIL thumbnail = NULL;
hr = DwmRegisterThumbnail(hwnd, FindWindow(_T("Progman"), NULL), &thumbnail);
if (SUCCEEDED(hr))
{
//destination rectangle size
RECT dest = {0,50,100,150};
//Set thumbnail properties for use
DWM_THUMBNAIL_PROPERTIES dskThumbProps;
dskThumbProps.dwFlags = DWM_TNP_RECTDESTINATION | DWM_TNP_VISIBLE | DWM_TNP_SOURCECLIENTAREAONLY;
//use window frame and client area
dskThumbProps.fSourceClientAreaOnly = FALSE;
dskThumbProps.fVisible = TRUE;
dskThumbProps.opacity = (255 * 70)/100;
dskThumbProps.rcDestination = dest;
//display the thumbnail
hr = DwmUpdateThumbnailProperties(thumbnail,&dskThumbProps);
if (SUCCEEDED(hr))
{
//do more things
}
}
return hr;
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