十三、File Translator怎么写

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1. File Translator可以将信息从maya中导入和导出。

2. 创建一个file translator需要从MPxFileTranslator继承。

3. 函数介绍：

　　（1）::canBeOpened()方法决定了file translator是否可以打开文件，如果只是一个importer那么就return flase，反之。

　　（2）importer：必须包含::haveReadMethod(), ::reader().

　　（3）exporter: 必须包含::haveWriteMethod(), ::writer().

4.设置translator允许访问所有的MEL命令：在MFnPlugin::registerTranslator()函数中将requireFullMel参数值设置成true.

5. 例子, 一个polygon的exporter：

class polyExporter:public MPxFileTranslator 
{
    public:
        polyExporter();
        virtual                ~polyExporter();
        virtual MStatus        writer (const MFileObject& file,
            const MString& optionsString, MPxFileTranslator::FileAccessMode mode);
        virtual bool           haveWriteMethod () const;
        virtual bool           haveReadMethod () const;
        virtual bool           canBeOpened () const;
        virtual MString        defaultExtension () const = 0;
    protected:    
        virtual bool           isVisible(MFnDagNode& fnDag, MStatus& status);
        virtual MStatus        exportAll(ostream& os);
        virtual MStatus        exportSelection(ostream& os);
       virtual void           writeHeader(ostream& os);
        virtual void           writeFooter(ostream& os);
        virtual MStatus        processPolyMesh(const MDagPath dagPath, ostream&    os);
        virtual polyWriter*    createPolyWriter(const MDagPath dagPath, MStatus& status) = 0;
};

6. MFnPlugin::registerFileTranslator()函数：

有6个参数，最后三个是可选的，

status = plugin.registerFileTranslator("RawText", "", polyRawExporter::creator, "", "option1=1", true);

RawText: is a name;

option1=1: default value for the option box for the translator;

true: means that you can use MGlobal::executeCommand() method in translator.

7. Reader:

　　如果要用reader()方法读取文件，那么haveReadMethod()方法要返回true

　　reader()方法读取文件的每一行，如果读取失败返回MS::kFailture

MStatus LepTranslator::reader ( const MFileObject& file,
    const MString& options, MPxFileTranslator::FileAccessMode mode)
{

    const MString fname = file.fullName();

 
    MStatus rval(MS::kSuccess);
    const int maxLineSize = 1024;
    char buf[maxLineSize];

    ifstream inputfile(fname.asChar(), ios::in);
    if (!inputfile) {
        // open failed
        cerr << fname << ": could not be opened for reading
";
        return MS::kFailure;
    }
    if (!inputfile.getline (buf, maxLineSize)) {
        cerr << "file " << fname << " contained no lines ... aborting
";
        return MS::kFailure;
    }
　　//the first line has the magic chars.
    if (0 != strncmp(buf, magic.asChar(), magic.length())) {
        cerr << "first line of file " << fname;
        cerr << " did not contain " << magic.asChar() << " ... aborting
";
        return MS::kFailure;
    }
    while (inputfile.getline (buf, maxLineSize)) { 
        //processing each line of the file
        MString cmdString;
        cmdString.set(buf);
        if (!MGlobal::executeCommand(cmdString))
            rval = MS::kFailure;
    }
    inputfile.close();
    return rval;
}

8. writer()方法, 类似reader()方法：

通过script editor来提供message，在这个例子中只提供export all 和export selection选项，其他的选项将输出failure message.

MStatus polyExporter::writer(const MFileObject& file,
    const MString& /*options*/,    MPxFileTranslator::FileAccessMode mode) 
{

        const MString fileName = file.fullName();
        ofstream newFile(fileName.asChar(), ios::out);
    if (!newFile) {
        MGlobal::displayError(fileName + ": could not be opened for reading");
        return MS::kFailure;
    }

    newFile.setf(ios::unitbuf);
    writeHeader(newFile);

    if (MPxFileTranslator::kExportAccessMode == mode) {
        if (MStatus::kFailure == exportAll(newFile)) {
            return MStatus::kFailure;
        }
    } 
    else if (MPxFileTranslator::kExportActiveAccessMode == mode) {
        if (MStatus::kFailure == exportSelection(newFile)) {
            return MStatus::kFailure;
        }
    } 
    else {
        return MStatus::kFailure;
    }
    writeFooter(newFile);
    newFile.flush();
    newFile.close();
    MGlobal::displayInfo("Export to " + fileName + " successful!");
    return MS::kSuccess;
}

9. file extention:

MString polyRawExporter::defaultExtension () const 
{
    return MString("raw");
}

10. file access mode: