OpenSceneGraph | OSG如何存储带纹理osgb格式可以节省空间

  在使用OSG（OpenSceneGraph）存储带纹理osgb格式的过程中，大家会遇到这样一种情况：存储后的osgb文件所占用的大小远大于原始文件的大小，几倍至几十倍。这是为何呢？原因是OSG默认的存储格式是不压缩存储，所以解决方案就是设置参数将存储格式改为压缩存储。方法如下：

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

  如下文档可以找到解决方法的来源：

$ 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
   }
}

　　

  上面文档中，有关WriteImageHint的项的描述（第26行）：选择IncludeData是直接写入数据，无压缩，是默认选项。而includeFile则是写入流，按我的理解，就是将原始的影像数据流原原本本的写入osgb，原始的影像是压缩过的，比如jpg格式，那保存出来的osgb就是压缩过的。因此，将WriteImageHint设置为IncludeFile可以解决OSG存储带纹理osgb格式数据量大的问题，节省空间。