Accessing .X Files

Regardless of the version of DirectX you are using (either DirectX 8 or 9), the methods you use to access .X files are the same. In fact, the interfaces have not changed names between the two newest versions of DirectX (8 and 9), making it possible for you to quickly port your version 8 code to the newer version 9 (and vice versa if you want).

The first step to accessing any .X file is to create an IDirectXFile interface.

Applications use the methods of the IDirectXFile interface to create instances of the IDirectXFileEnumObject and IDirectXFileSaveObject interfaces, and to register templates. Deprecated.

IDirectXFile Members

Remarks

The globally unique identifier (GUID) for the IDirectXFile interface is IID_IDirectXFile.

The IDirectXFile interface is obtained by calling the DirectXFileCreate function.

The LPDIRECTXFILE type is defined as a pointer to this interface.

typedef interface IDirectXFile *LPDIRECTXFILE;

You need to call the DirectXFileCreate function, as shown in the following bit of code:

IDirectXFile *pDXFile = NULL;
HRESULT Result = DirectXFileCreate(&pDXFile);

As you can see from the previous lines of code, the DirectXFileCreate function takes one parameter−the pointer to an IDirectXFile interface. You can quickly determine whether the function has succeeded in creating a valid, IDirectXFile interface by using the SUCCEEDED or FAILED macro on the return code from the DirectXFileCreate call.

Once you've successfully created the IDirectXFile interface, you can optionally register any templates you'll be using (such as the DirectX standard templates) and create an enumeration interface that weeds through the top−level data objects within your .X files.

Registering Custom and Standard Templates

To save storage space and improve your data security, the .X interfaces allow you to remove all template definitions from .X files and embed them into your executable. This means that instead of the .X files defining templates, your program has to do it. Don't worry−it's not as difficult as it sounds. As you'll see in a moment, Microsoft has taken the liberty of doing the hard work by defining the standard templates inside a couple include files, making everything as simple as possible.

To register the standard templates (or any template, for that matter) from within your program, you'll need to call upon the IDirectXFile::RegisterTemplates function.

HRESULT IDirectXFile::RegisterTemplates(
  LPVOID pvData, // buffer containing template definitions
  DWORD cbSize); // # of bytes of data

The pvData parameter is merely a data buffer that contains the template definitions in the exact format you'd see in an .X file. For example, you can define a template data buffer like this:

char *Templates = "
"xof 0303txt 0032 \
template CustomTemplate { \
<4c944580−9e9a−11cf−ab43−0120af71e433> \
DWORD Length; \
array DWORD Values[Length]; \
}";

Note Notice that the template definition in Templates uses the backslash character to represent a new line, and that the first line of text is a standard .X file header.

Going back to RegisterTemplates, the cbSize parameter represents the size of the template data buffer, which you can determine in this case by using the strlen of the Templates buffer. Put together, you can register the templates defined in Templates using the following code:

pFile−>RegisterTemplates(Templates, strlen(Templates));

Now let's get back to the topic at hand−registering the standard templates. You've seen RegisterTemplates at work. In order to register the standard templates, you need to include two additional files in your project−rmxftmpl.h and rmxfguid.h. These two files define the template definitions and GUIDs of the standard templates, respectively.

Tip To remember rmxftmpl.h and rmxfguid.h, just remember that rmxf stands for retained mode x−file, tmpl means template, and guid means globally unique identifier.

Inside the rmxftmpl.h file, you'll find the D3DRM_XTEMPLATES template data buffer and the D3DRM_XTEMPLATE_BYTES macro. These are used in the call to RegisterTemplates to register the standard templates, as you can see here:

pFile−>RegisterTemplates(D3DRM_XTEMPLATES,  D3DRM_XTEMPLATE_BYTES);

That's right; just by calling the above bit of code, you have successfully registered the standard templates, and you're ready to move on! A word of advice before you do: Once you begin using the .X format for your own custom templates and data, don't forget that using RegisterTemplates works perfectly for registering your own custom template definitions!

Opening an .X File

After you've created an IDirectXFile interface and registered the templates you'll be using, you need to open the .X file and begin enumerating the data objects within it. The process of opening the .X file and creating an enumeration object occurs in one call to the IDirectXFile::CreateEnumObject function.

HRESULT IDirectXfile::CreateEnumObject(
  LPVOID pvSource, // .X filename
  DXFILELOADOPTIONS dwLoadOptions, // Load options
  LPDIRECTXFILEENUMOBJECT* ppEnumObj); // Enum interface

When you call the CreateEnumObject function, specify the file name of the .X file to load as pvSource and the interface you'll be using as ppEnumObj. As for dwLoadOptions, you should specify the value DXFILELOAD_FROMFILE, which tells DirectX to load the file from disk. Other possible values for dwLoadOptions are DXFILELOAD_FROMRESOURCE, DXFILELOAD_FROMMEMORY, and DXFILELOAD_FROMURL. These values tell DirectX to load the .X file from a resource, memory buffer, or network URL, respectively. Yep, that's right−you can load .X files directly over the Internet!

Tip To load an .X file from the Internet using a URL, specify the complete network path in pvSource.To load from a resource or memory location, just specify the resource handle or memory pointer (both cast as LPVOID) in pvSource.

Continue the example and create an enumeration object for the .X file. The following code will create an enumeration object used to parse a file from a disk.

// Filename = filename to load ("test.x" for example)
IDirectXFileEnumObject *pEnum;
pFile−>CreateEnumObject((LPVOID)Filename, DXFILELOAD_FROMFILE, &pEnum);

From the code's comments, you can see that Filename points to a valid file name−in this case, test.x. Once successfully called, the CreateEnumObject gives you a valid enumeration object (only one is required per open .X file), ready to do all your enumeration dirty work.