OpenSceneGraph | OSG如何存儲帶紋理osgb格式可以節省空間

  在使用OSG（OpenSceneGraph）存儲帶紋理osgb格式的過程中，大家會遇到這樣一種情況：存儲後的osgb文件所佔用的大小遠大於原始文件的大小，幾倍至幾十倍。這是爲何呢？原因是OSG默認的存儲格式是不壓縮存儲，所以解決方案就是設置參數將存儲格式改爲壓縮存儲。方法如下：

osg::ref_ptr<osgDB::ReaderWriter::Options> options = new osgDB::ReaderWriter::Options;
options->setOptionString("WriteImageHint=IncludeFile");			// 設置壓縮
osgDB::writeNodeFile(*(node.get()), osgb_path, options);

  如下文檔可以找到解決方法的來源：

$ osgconv --format osgb 
Plugin osgPlugins-3.3.9/osgdb_osg.so 
{ 
   ReaderWriter : OSG Reader/Writer 
   { 
       features   : readObject readNode writeObject writeNode   
       extensions : .osg                           OpenSceneGraph Ascii file format 
       extensions : .osgs                          Pseudo OpenSceneGraph file loaded, with file encoded in filename string 
       options    : OutputTextureFiles             Write out the texture images to file 
       options    : includeExternalReferences      Export option 
       options    : precision                      Set the floating point precision when writing out files 
       options    : writeExternalReferenceFiles    Export option 
   } 
   ReaderWriter : OpenSceneGraph Native Format Reader/Writer 
   { 
       features   : readObject readImage readNode writeObject writeImage writeNode   
       extensions : .osg2                    OpenSceneGraph extendable format 
       extensions : .osgb                    OpenSceneGraph extendable binary format 
       extensions : .osgt                    OpenSceneGraph extendable ascii format 
       extensions : .osgx                    OpenSceneGraph extendable XML format 
       options    : Ascii                    Import/Export option: Force reading/writing ascii file 
       options    : Compressor=<name>        Export option: Use an inbuilt or user-defined compressor 
       options    : ForceReadingImage        Import option: Load an empty image instead if required file missed 
       options    : SchemaData               Export option: Record inbuilt schema data into a binary file 
       options    : SchemaFile=<file>        Import/Export option: Use/Record an ascii schema file 
       options    : WriteImageHint=<hint>    Export option: Hint of writing image to stream: <IncludeData> writes Image::data() directly; <IncludeFile> writes the image file itself to stream; <UseExternal> writes only the fi 
lename; <WriteOut> writes Image::data() to disk as external file. 
       options    : XML                      Import/Export option: Force reading/writing XML file 
   } 
} 

  上面文檔中，有關WriteImageHint的項的描述（第26行）：選擇IncludeData是直接寫入數據，無壓縮，是默認選項。而includeFile則是寫入流，按我的理解，就是將原始的影像數據流原原本本的寫入osgb，原始的影像是壓縮過的，比如jpg格式，那保存出來的osgb就是壓縮過的。因此，將WriteImageHint設置爲IncludeFile可以解決OSG存儲帶紋理osgb格式數據量大的問題，節省空間。