Detailed Description

Translator to output filtered Maya ASCII files.

MPxMayaAsciiFilter allows output to the Maya ASCII (.ma) file format to be filtered by a plug-in. The file is output using the same internal mechanism that is used for normal Maya ASCII output, but allows your plug-in to prevent certain lines (such as createNodes or connectAttrs) from being output to the file. In addition, it allows you to write directly to the file at specific points during output.

MPxMayaAsciiFilter allows your plug-in to write out files similar to Maya ASCII in a custom format. It can be used, for example, to partition a scene into several files, each of which has been filtered to write out different parts of the scene. Note that the order of the file cannot be changed - for example, connectAttrs are always written after createNodes - but it does allow you to control which connectAttrs and createNodes are output.

MPxMayaAsciiFilter inherits from MPxFileTranslator. It overrides the haveWriteMethod(), haveReadMethod(), reader(), and writer() methods in MPxFileTranslator in such a way that the internal Maya mechanism for reading and writing Maya ASCII files is used. Because of this, it is not advised that you override these methods in your plug-in. If you do, make sure you first call these methods in MPxMayaAsciiFilter. A pseudo-code example is shown here:

MyAsciiFilter::writer(...)
{
    // do something before writing to file here
    ...

    // we will now write to the file

    MStatus result = MPxMayaAsciiFilter::writer(...);

    if (result == MStatus::kSuccess)
    {
        ... // do something after writing the file here
    }

    return result;
}

To determine if a given line should be output, override the methods writesCreateNode(), writesSetAttr() and so on. Each of these methods takes as its arguments the relevant data which is about to be processed and your plug-in can use this to determine whether or not the line will be output.

For example, you may want to write out everything but render layer data. The code to do this might look something like what is shown here:

bool
MyAsciiFilter::writesCreateNode( const MObject& node )
{
    if (node.hasFn(MFn::kRenderLayer))
    {
        return true;
    }

    return false;
}

bool
MyAsciiFilter::writesConnectAttr( const MPlug& srcPlug,
                                  const MPlug& destPlug )
{
    if (srcPlug.node().hasFn(MFn::kRenderLayer) ||
        dstPlug.node().hasFn(MFn::kRenderLayer))
    {
        return true;
    }

    return false;
}

Note that writesConnectAttr() has to be overridden as well (as would writesSetAttr(), writesSelectAttr(), and so on). This is because each line is handled separately, and nothing clever is done in the base class' implementation of writesConnectAttr(), such as having a default behaviour of only outputting connectAttrs for nodes that are being output. This gives you the most flexible control over what will be written.

If you were using this class to save a segmented file, a master file might have to know about the locations of each of the segments. If your file saved everything but render layers in one file, and render layers in another, the first file might need to contain a pointer to the second, so that when the first file is loaded the second gets read into memory too. To do this, you would use MPxMayaAsciiFilter's ability to write directly to the stream during file output.

You can write to the stream during output by overriding the methods writePreCreateNodesBlock(), writePostCreateNodesBlock() and so on. These give you a simple mechanism to write directly to the file. Each of these methods take an MPxMayaAsciiFilterOutput as its only argument. To write to the file, simply use the output operator (MPxMayaAsciiFilterOutput::operator<<() ) and output the string you wish.

In the example above, the pointer to the render layer file might be inserted into the main file after all nodes have been created. The code to do this would look something like what is shown here:

MStatus
MyAsciiFilter::writePostCreateNodesBlock( MPxMayaAsciiFilterOutput& fileIO )
{
    fileIO << "eval(\"importRenderLayerFile \\\"MyLayerFile.maf\\\";\")\n";
}

In the above example, after the createNode block was output, the line

eval("importRenderLayerFile \"MyLayerFile.maf\"");

was output. When the file is read in, Maya would reach the line above and execute it like any other MEL command. It is assumed in this example that there would be a custom command plug-in called importRenderLayerFile which would do the work of actually importing the layer file.

Note: MPxMayaAsciiFilter gives you the ability to create your own custom file formats based on standard Maya ASCII files. However, Autodesk does not support such custom files as they will not, by definition, be standard Maya ASCII files.

Examples:: filteredAsciiFile.cpp.

#include <MPxMayaAsciiFilter.h>

Inheritance diagram for MPxMayaAsciiFilter:

[legend]

List of all members.

Public Member Functions
	MPxMayaAsciiFilter ()
	The class constructor.
virtual	~MPxMayaAsciiFilter ()
	The class destructor.
virtual bool	haveWriteMethod () const
	Overrides MPxFileTranslator::haveWriteMethod() to indicate that this translator has a write method.
virtual bool	haveReadMethod () const
	Overrides MPxFileTranslator::haveReadMethod() to indicate that this translator has a read method.
virtual MStatus	reader (const MFileObject &file, const MString &optionsString, FileAccessMode mode)
	Reader method for the ascii filter translator.
virtual MStatus	writer (const MFileObject &file, const MString &optionsString, FileAccessMode mode)
	Writer method for the ascii filter translator.
Protected Member Functions
const MFileObject	file () const
	Returns the MFileObject associated with the file currently being read or written, allowing access to the file's name, path and so on.
virtual MStatus	processReadOptions (const MString &optionsString)
	Allows the translator to handle any options passed into the reader() method, above.
virtual MStatus	processWriteOptions (const MString &optionsString)
	Allows the translator to handle any options passed into the reader() method, above.
virtual bool	writesRequirements () const
	Determines if "requires" commands should be written in the file.
virtual bool	writesCreateNode (const MObject &node) const
	Determines if a "createNode" command should be written for a particular node.
virtual bool	writesSetAttr (const MPlug &srcPlug) const
	Determines if a "setAttr" command should be written for a particular node.
virtual bool	writesConnectAttr (const MPlug &srcPlug, const MPlug &destPlug) const
	Determines if a "connectAttr" command should be written for a particular node.
virtual bool	writesDisconnectAttr (const MPlug &srcPlug, const MPlug &destPlug) const
	Determines if a "disconnectAttr" command should be written for a particular connection.
virtual bool	writesParentNode (const MDagPath &parent, const MDagPath &child) const
	Determines if a "parent" command should be written for a particular parent and child.
virtual bool	writesSelectNode (const MObject &node) const
	Determines if a "select" command should be written for a particular node.
virtual bool	writesFileReference (const MFileObject &referenceFile) const
	Determines if a "fileReference" command should be written for a file.
virtual MStatus	writePostHeader (MPxMayaAsciiFilterOutput &fileIO)
	Allows data to be written out to the file after the header block.
virtual MStatus	writePostRequires (MPxMayaAsciiFilterOutput &fileIO)
	Allows data to be written out to the file after the requires block.
virtual MStatus	writePreCreateNodesBlock (MPxMayaAsciiFilterOutput &fileIO)
	Allows data to be written out to the file before the create nodes block.
virtual MStatus	writePostCreateNodesBlock (MPxMayaAsciiFilterOutput &fileIO)
	Allows data to be written out to the file after the create nodes block.
virtual MStatus	writePreConnectAttrsBlock (MPxMayaAsciiFilterOutput &fileIO)
	Allows data to be written out to the file before the connect attrs block.
virtual MStatus	writePostConnectAttrsBlock (MPxMayaAsciiFilterOutput &fileIO)
	Allows data to be written out to the file after the connect attrs block.
virtual MStatus	writePreTrailer (MPxMayaAsciiFilterOutput &fileIO)
	Allows data to be written out to the file before the trailer block.

Member Function Documentation

bool haveWriteMethod ( ) const [virtual]

MStatus reader	(	const MFileObject &	file,
		const MString &	optionsString,
		FileAccessMode	mode
	)		`[virtual]`

[in]	file	The file to be read
[in]	optionsString	Any file options to be handled. Passed to processReadOptions(), below
[in]	mode	The access mode (read or import). Currently this is ignored

MStatus writer	(	const MFileObject &	file,
		const MString &	optionsString,
		FileAccessMode	mode
	)		`[virtual]`

bool writesConnectAttr	(	const MPlug &	srcPlug,
		const MPlug &	destPlug
	)		const `[protected, virtual]`

[in]	srcPlug	The source plug in the connection.
[in]	destPlug	The destination plug in the connection.

bool writesDisconnectAttr	(	const MPlug &	srcPlug,
		const MPlug &	destPlug
	)		const `[protected, virtual]`

bool writesParentNode	(	const MDagPath &	parent,
		const MDagPath &	child
	)		const `[protected, virtual]`

[in]	parent	The dag path to the parent.
[in]	child	The dag path to the child.

MPxMayaAsciiFilter Class Reference

OpenMaya - API module for common classes | Proxy classes

Detailed Description

Public Member Functions

Protected Member Functions

Member Function Documentation