Most of the object-creation functions in the OLE API work in exactly the same way when they are renamed and used by object-handler DLLs. Two functions are somewhat different, however: OleCreateFromClip and OleLoadFromStream.
When the client library calls the DllCreateFromClip function, the library includes a parameter that is not specified in the original call to the OleCreateFromClip function. This parameter, objtype, specifies whether the object being created is an embedded object or a link; its value can be either OT_LINK or OT_EMBEDDED.
The following syntax block shows the objtype parameter when an object handler uses the DefCreateFromClip function. The DllCreateFromClip function has exactly the same syntax as DefCreateFromClip. For a full description of all the parameters, see the description of the OleCreateFromClip function in the Microsoft Windows Programmer's Reference, Volume 2.
OLESTATUS DefCreateFromClip(lpszProtocol, lpclient, lhclientdoc,
lpszObjname, lplpobject, renderopt, cfFormat, objtype);
LPSTR lpszProtocol; /* address of string for protocol name */
LPOLECLIENT lpclient; /* address of client structure */
LHCLIENTDOC lhclientdoc; /* long handle of client document */
LPSTR lpszObjname; /* string for object name */
LPOLEOBJECT FAR * lplpobject; /* address of pointer to object */
OLEOPT_RENDER renderopt; /* rendering options */
OLECLIPFORMAT cfFormat; /* clipboard format */
LONG objtype; /* OT_LINKED or OT_EMBEDDED */If DllCreateFromClip calls DefCreateFromClip, DllCreateFromClip should pass it the objtype parameter along with the other parameters from the version of DefCreateFromClip that was exported by the client library. DllCreateFromClip can modify some of these parameters before passing them back to DefCreateFromClip. For example, the object handler could specify a different value for the renderopt parameter when it calls DefCreateFromClip. If the client calls this function with olerender_draw for renderopt and the handler performs the drawing with Native data, the handler could change olerender_draw to olerender_none. If the client calls this function with olerender_draw for renderopt and the handler calls the GetData function and performs the drawing based on a class-specific format, the handler could change olerender_draw to olerender_format. If the handler needed a different rendering format than the format specified by the client application, the object handler could also change the value of the cfFormat parameter in the call to DefCreateFromClip.
If an object handler uses Native data to render an embedded object, the handler can call the library and specify olerender_none. If a handler uses Native data to render a linked object, it can use olerender_format and specify Native data. When the handler's Draw function is called, the handler calls the GetData function, specifying Native data, to do the rendering. If a handler uses a private data format, the procedure is the same—except that the private format is specified with the olerender_format option and with the GetData function.
When the client library calls the DllLoadFromStream function, the library includes three parameters that are not specified in the original call to the OleLoadFromStream function. One of the additional parameters is objtype, as described for DefCreateFromClip and DllCreateFromClip. The other two parameters are aClass, which is an atom containing the class name for the object, and cfFormat, which specifies a private clipboard format that the object handler can use for rendering the object.
The following syntax block shows the objtype, aClass, and cfFormat parameters when an object handler uses the DefLoadFromStream function. The DllLoadFromStream function has exactly the same syntax as DefLoadFromStream. For a full description of all the parameters, see the description of the OleLoadFromStream function in the Microsoft Windows Programmer's Reference, Volume 2.
OLESTATUS DefLoadFromStream(lpstream, lpszProtocol, lpclient,
lhclientdoc, lpszObjname, lplpobject, objtype, aClass, cfFormat);
LPOLESTREAM lpstream; /* address of stream for object */
LPSTR lpszProtocol; /* address of string for protocol name */
LPOLECLIENT lpclient; /* address of client structure */
LHCLIENTDOC lhclientdoc; /* long handle of client document */
LPSTR lpszObjname; /* string for object name */
LPOLEOBJECT FAR * lplpobject; /* address of pointer to object */
LONG objtype; /* OT_LINKED or OT_EMBEDDED */
ATOM aClass; /* atom containing object's class name */
OLECLIPFORMAT cfFormat; /* private data format for rendering */If DllLoadFromStream calls DefLoadFromStream, DllLoadFromStream should pass it the three additional parameters along with the other parameters from the version of DefLoadFromStream that was exported by the client library.DllLoadFromStream can modify some of these parameters before passing them back to DefLoadFromStream. For example, the object handler could modify the value of the cfFormat parameter to specify a private data format it would use to render the object.
When the client calls the object handler with DefLoadFromStream, the handler uses the Get function from the OLESTREAMVTBL structure to obtain the data for the object.