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How to parse .X files

By Jim Adams | Published Sep 13 2001 05:44 PM in DirectX and XNA

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Copyright © 2001 by Jim Adams. All rights reserved.

One of the greatest, and most confusing, additions to Direct3D is that of skinned meshes. These miraculous mesh marvels allow the user to dynamically deform a mesh in order to produce animation. Unfortunately, Microsoft screwed the pooch when it came time to effectively demonstrate and document the use of skinned meshes.

As you can tell from the title of this article, I'm not here to tackle the subject of skinned meshes, but rather to build a base of understanding of the file format you're most likely to use when dealing with skinned meshes: .X files. To be more precise, I'm only going to show you how to parse an .X file; specifically how to read in the data contained within an .X file.

Now don't throw your hands up in the air asking what good this does you! In fact, understanding how to parse an .X file template by template is the first big step you'll take to loading and using skinned meshes.


The .X File Objects

DirectX comes with a set of objects that have the sole responsibility of dealing with .X files. This functionality includes opening the .X files, enumerating contained templates, and saving templates. Those objects we're most interested in at this point are:
  • IDirectXFile
    The main object that opens an .X file for use.
  • IDirectXFileEnumObject
    An object that enumerates templates within an .X file.
  • IDirectXFileData
    An object that represents the data contained with a template.
  • IDirectXFileObject
    A minor object that represents data within an .X file.
  • IDirectXFileDataReference
    The object used to resolve template references contained within .X files.
Note that in order to use the family of DirectX file objects, you'll have to include dxfile.h into your project, as well as linking to the d3dx8of.lib library. Make sure to also link with dxguid.lib to make sure your GUID's are defined for you!


Parsing in two easy functions

Well, you've met the gang of objects and now it's time to put them to work. I'm going to give you two quick and easy functions that does all the work for you of parsing .X files. The first function, called ParseXFile, is the only one you will call directly (a public callable function if you will).

The ParseXFile function has the job of initializing the IDirectXFile object, which in turns opens the specified .X file. From there, you have to register a list of templates you expect to find within the .X file; this list is contained within a series of headers provided with Direct3D.

Next, the ParseXFile function will create an enumeration object (IDirectXFileEnumObject) that begins scanning through the top-most templates. As each top-level template is found, it is passed to the second function, ParseXFileData. Once all top-level templates are parsed, all DirectX file objects are released and execution returns to the calling function.

The ParseXFileData function does the majority of the work here. It retrieves the GUID of the currently enumerated template, as well the specified template instance name (if any name was provided). From there, you'll come in and see what to do with the template (based on its GUID). In the sample code provided with this article, I have listed a few standard Direct3D templates you're bound to use.

Moving on, the ParseXFileData function then scans for sub-templates; that is, templates that are embedded within other templates. This process takes into account that some templates are merely references to template instances defined elsewhere in the .X file, and as such, the references are resolved and parsed. As each sub-template is found, it is recursively passed to the ParseXFileData function to parse. This process continues until all sub-templates are parsed and execution returns to the ParseXFile function.

I really don't have the time or space to show you the breakdown of every DirectX file object and their respective interfaces, but rather I have fully commented the code to help you understand what's going on.

So without further ado, here's the code for the two functions:

BOOL ParseXFile(char *Filename)
{
  IDirectXFile   		*pDXFile = NULL;
  IDirectXFileEnumObject *pDXEnum = NULL;
  IDirectXFileData   	*pDXData = NULL;

  // Create the .X file object
  if(FAILED(DirectXFileCreate(&pDXFile)))
	return FALSE;

  // Register the templates in use
  // Use the standard retained mode templates from Direct3D
  if(FAILED(pDXFile->RegisterTemplates((LPVOID)D3DRM_XTEMPLATES, D3DRM_XTEMPLATE_BYTES))) {
	pDXFile->Release();
	return FALSE;
  }

  // Create an enumeration object
  if(FAILED(pDXFile->CreateEnumObject((LPVOID)Filename, DXFILELOAD_FROMFILE, &pDXEnum))) {
	pDXFile->Release();
	return FALSE;
  }

  // Enumerate all top-level templates
  while(SUCCEEDED(pDXEnum->GetNextDataObject(&pDXData))) {
	ParseXFileData(pDXData);
	ReleaseCOM(pDXData);
  }

  // Release objects
  ReleaseCOM(pDXEnum);
  ReleaseCOM(pDXFile);

  // Return a success
  return TRUE;
}

void ParseXFileData(IDirectXFileData *pData)
{
  IDirectXFileObject *pSubObj  = NULL;
  IDirectXFileData   *pSubData = NULL;
  IDirectXFileDataReference *pDataRef = NULL;
  const GUID *pType = NULL;
  char   	*pName = NULL;
  DWORD   	dwSize;
  char   	*pBuffer;
  
  // Get the template type
  if(FAILED(pData->GetType(&pType)))
	return;

  // Get the template name (if any)
  if(FAILED(pData->GetName(NULL, &dwSize)))
	return;
  if(dwSize) {
	if((pName = new char[dwSize]) != NULL)
  	pData->GetName(pName, &dwSize);
  }

  // Give template a default name if none found
  if(pName == NULL) {
	if((pName = new char[9]) == NULL)
  	return;
	strcpy(pName, "Template");
  }

  // See what the template was and deal with it
  // This is where you'll jump in with your own code

  if(*pType == TID_D3DRMFrame) {
	MessageBox(NULL, pName, "Frame template found", MB_OK);
  }

  if(*pType == TID_D3DRMMesh) {
	MessageBox(NULL, pName, "Mesh template found", MB_OK);
  }

  if(*pType == TID_D3DRMMaterial) {
	MessageBox(NULL, pName, "Material template found", MB_OK);
  }

  if(*pType == TID_D3DRMFrameTransformMatrix) {
	MessageBox(NULL, pName, "Frame transformation matrix template found", MB_OK);

	// Get the template data
	if(FAILED(pData->GetData(NULL, &dwSize, (PVOID*)&pBuffer)))
  	return;

	// Do whatever with data. Note that you can cast
	// the pointer to anything. Be sure to copy data 
	// out of buffer before proceeding.
   }

  // Scan for embedded templates
  while(SUCCEEDED(pData->GetNextObject(&pSubObj))) {

	// Process embedded references
	if(SUCCEEDED(pSubObj->QueryInterface(IID_IDirectXFileDataReference, (void**)&pDataRef))) {
  	if(SUCCEEDED(pDataRef->Resolve(&pSubData))) {
    	ParseXFileData(pSubData);
    	ReleaseCOM(pSubData);
  	}
  	ReleaseCOM(pDataRef);
	}

	// Process non-referenced embedded templates
	if(SUCCEEDED(pSubObj->QueryInterface(IID_IDirectXFileData, (void**)&pSubData))) {
  	ParseXFileData(pSubData);
  	ReleaseCOM(pSubData);
	}
	ReleaseCOM(pSubObj);
  }

  // Release name buffer
  delete pName;
}


What to do from here

You may be asking, "What do I do with those two functions?" You can see I quickly added a few statements in there to check for a couple standard templates, and to display a message box informing you when those templates are found. All you have to do is provide the ParseXFile function with an .X file to work with. Go ahead and check out the accompanying demo that comes with this article for a short example of using the two functions.

To get back to the original points I made when I first started the article, parsing .X files is essential to working with skinned meshes. By tracking the frame templates as they are parsed, you're able to construct a frame hierarchy, which is used to create the underlying bone structure required for skinned meshes. Once a mesh template is encountered, you can then utilize the D3DXLoadMeshFromXof or D3DXLoadSkinMeshFromXof set of functions to load the mesh data into a useable object. Consult the DX SDK documents for more information on those two functions.







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