十3、File Translator怎麼寫

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1. File Translator能夠將信息從maya中導入和導出。

2. 建立一個file translator須要從MPxFileTranslator繼承。

3. 函數介紹：

　　（1）::canBeOpened()方法決定了file translator是否能夠打開文件，若是隻是一個importer那麼就return flase，反之。

　　（2）importer：必須包含::haveReadMethod(), ::reader().

　　（3）exporter: 必須包含::haveWriteMethod(), ::writer().

 

4.設置translator容許訪問全部的MEL命令： 在MFnPlugin::registerTranslator()函數中將requireFullMel參數值設置成true.

5. 例子, 一個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()函數：

有6個參數，最後三個是可選的，

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:

　　若是要用reader()方法讀取文件，那麼haveReadMethod()方法要返回true

　　reader()方法讀取文件的每一行，若是讀取失敗返回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\n";
        return MS::kFailure;
    }
    if (!inputfile.getline (buf, maxLineSize)) {
        cerr << "file " << fname << " contained no lines ... aborting\n";
        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\n";
        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, 相似reader()方法：

經過script editor來提供message，在這個例子中只提供export all 和export selection選項，其餘的選項將輸出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: