osg--读写

文件I/O

命名规则

osgdb_xxx

比如：

osgdb_osg
osgdb_jpeg 

关联文件后缀和加载器

osgDB::Registry::instance()->addFileExtensionAlias( "jpeg", "jpeg" );
osgDB::Registry::instance()->addFileExtensionAlias( "jpg", "jpeg" );

使用

osg::Node* node = osgDB::readNodeFile( "cow.osg" );
osg::Image* image = osgDB::readImageFile( "Images/lz.rgb" );

说明

加载文件两个步骤

1. osgDB::Registry
   • 单一实例
   • 管理着常用文件I/O插件列表
   • 逐一向下传递
2. 外部共享模块

已支持

伪加载

并非实际的文件后缀

自定义加载

osgDB::ReaderWriter

• supportsExtension

• acceptsExtension

• fileExists

• readNode

    osgDB::ReaderWriter::ReadResult readNode(const std::string& file,const osgDB::Options* options) const
    {
        // Check if the file extension is recognizable and file exists
        bool recognizableExtension = …;
        bool fileExists = …;
        if (!recognizableExtension) return ReadResult::FILE_NOT_HANDLED;
        if (!fileExists) return ReadResult::FILE_NOT_FOUND;
        …
        // Construct the scene graph according to format specification
        osg::Node* root = …;
        …
        // In case there are fatal errors during the process,
        // return an invalid message; otherwise return the root node
        bool errorInParsing = …;
        if (!errorInParsing) return ReadResult::ERROR_IN_READING_FILE;
        return root;
    }
  

  • osgDB::ReaderWriter::ReadResult重载构造器
    • node
    • image
    • status enumeration
    • other special object
    • error message string
    • 方法
      • success
      • takeNode
  • osgDB::Options
    • setOptionString
    • getOptionString
    • 直接传入readNodeFile第二个参数

• writeNode

• readImage

• writeImage

流加载

1. 定义读写接口

    osgDB::ReaderWriter::ReadResult readNode(const std::string& file,const osgDB::Options* options) const
    {
        …
        osgDB::ifstream stream( file.c_str(), std::ios::binary );
        if ( !stream ) return ReadResult::ERROR_IN_READING_FILE;
        return readNode(stream, options);
    }
    
    osgDB::ReaderWriter::ReadResult readNode(std::istream& stream,const osgDB::Options* options) const
    {
        // Construct the scene graph according to format specification
        osg::Node* root = …;
        return root;
    }
   

2. 利用已有读写器处理流

    osgDB::ReaderWriter* rw =osgDB::Registry::instance()->getReaderWriterForExtension("osg");
    if (rw)
    {
        osgDB::ReaderWriter::ReadResult rr = reader->readNode(stream);
        if ( rr.success() )
            node = rr.takeNode();
    }
   

示例

CMakeLists.txt

add_library( osgdb_tri SHARED readerwriter.cpp )

readerwriter.cpp

#include <osg/Geometry>
#include <osg/Geode>
#include <osgDB/FileNameUtils>
#include <osgDB/FileUtils>
#include <osgDB/Registry>
#include <osgUtil/SmoothingVisitor>
#include <iostream>

class ReaderWriterTRI : public osgDB::ReaderWriter
{
public:
	ReaderWriterTRI();

	virtual ReadResult readNode(
		const std::string&, const osgDB::ReaderWriter::Options*)
		const;
	virtual ReadResult readNode(
		std::istream&, const osgDB::ReaderWriter::Options*) const;
};
ReaderWriterTRI::ReaderWriterTRI()
{
	supportsExtension("tri", "Triangle strip points");
}
ReaderWriterTRI::ReadResult ReaderWriterTRI::readNode(
	const std::string& file, const osgDB::ReaderWriter::Options* options)
	const
{
	std::string ext = osgDB::getLowerCaseFileExtension(file);
	if (!acceptsExtension(ext)) 
		return ReadResult::FILE_NOT_HANDLED; 
	std::string fileName = osgDB::findDataFile(file, options);
	if (fileName.empty()) 
		return ReadResult::FILE_NOT_FOUND;
	std::ifstream stream(fileName.c_str(), std::ios::in);
	if (!stream) 
		return ReadResult::ERROR_IN_READING_FILE;
	return readNode(stream, options);
}
ReaderWriterTRI::ReadResult ReaderWriterTRI::readNode(
	std::istream& stream, const osgDB::ReaderWriter::Options*) const
{
	unsigned int index = 0, numPoints = 0;
	stream >> numPoints;

	osg::ref_ptr<osg::Vec3Array> va = new osg::Vec3Array;
	while (index<numPoints && !stream.eof() &&
		!(stream.rdstate()&std::istream::failbit))
	{
		osg::Vec3 point;
		stream >> point.x() >> point.y() >> point.z();
		va->push_back(point);
		index++;
	}


	osg::ref_ptr<osg::Geometry> geom = new osg::Geometry;
	geom->setVertexArray(va.get());
	geom->addPrimitiveSet(
		new osg::DrawArrays(GL_TRIANGLE_STRIP, 0, numPoints));


	osgUtil::SmoothingVisitor smoother;
	smoother.smooth(*geom);


	osg::ref_ptr<osg::Geode> geode = new osg::Geode;
	geode->addDrawable(geom.get());
	return geode.release();
}
REGISTER_OSGPLUGIN(tri, ReaderWriterTRI);

使用

osgviewer example.tri

序列化osg格式

前提

• 继承osg::Object
• META_Object 正确定义命名空间和类名
• 每一个成员变量需要有getter和setter方法

示例

#include <osg/Node>
#include <osgDB/ObjectWrapper>
#include <osgDB/Registry>
#include <osgDB/ReadFile>
#include <osgDB/WriteFile>
#include <iostream>

namespace testNS {
class ExampleNode : public osg::Node
{
public:
    ExampleNode() : osg::Node(), _exampleID(0) {}
    
    ExampleNode(const ExampleNode& copy,const osg::CopyOp& copyop=osg::CopyOp::SHALLOW_COPY)
    : osg::Node(copy, copyop), _exampleID(copy._exampleID) {}
    

    META_Node(testNS, ExampleNode)
    

    void setExampleID( unsigned int id ) { _exampleID = id; }
    unsigned int getExampleID() const { return _exampleID; }
    

protected:
    unsigned int _exampleID;
};
}
REGISTER_OBJECT_WRAPPER( ExampleNode_Wrapper,new testNS::ExampleNode,testNS::ExampleNode,"osg::Object osg::Node testNS::ExampleNode" )
{
    ADD_UINT_SERIALIZER( ExampleID, 0 );
}
int main(int argc, char** argv)
{
	osg::ArgumentParser arguments( &argc, argv );
	unsigned int writingValue = 0;
	arguments.read( "-w", writingValue );
	
	if ( writingValue!=0 )
	{
		osg::ref_ptr<testNS::ExampleNode> node = new testNS::ExampleNode;
		node->setExampleID( writingValue );
		osgDB::writeNodeFile( *node, "examplenode.osgt" );
	}else
	{
		testNS::ExampleNode* node = dynamic_cast<testNS::ExampleNode*>(osgDB::readNodeFile("examplenode.osgt") );
		if ( node!=NULL )
		{
			std::cout << "Example ID: " << node->getExampleID() << std::endl;
		}
	}
}