Introduce C entry point support for plugin setup for better static build support

include/osgDB/Registry

@@ -565,6 +565,29 @@ class RegisterReaderWriterProxy
         osg::ref_ptr<T> _rw;
 };
 
+extern "C"
+{
+    typedef void (* CPluginFunction) (void);
+}
+
+class PluginFunctionProxy
+{
+public:
+
+    PluginFunctionProxy(CPluginFunction function)
+    {
+        (function)();
+    }
+};
+
+#define USE_OSGPLUGIN(ext) \
+    extern "C" void osgdb_##ext(void); \
+    static osgDB::PluginFunctionProxy proxy_##ext(osgdb_##ext);
+
+#define REGISTER_OSGPLUGIN(ext, classname) \
+    extern "C" void osgdb_##ext(void) {} \
+    static RegisterReaderWriterProxy<classname> g_proxy_##classname;
+
 }
 
 #endif

src/osgPlugins/ive/ReaderWriterIVE.cpp

@@ -10,7 +10,7 @@
 using namespace osg;
 using namespace osgDB;
 
-class IVEReaderWriter : public ReaderWriter
+class ReaderWriterIVE : public ReaderWriter
 {
     public:
         virtual const char* className() const { return "IVE Reader/Writer"; }
@@ -186,4 +186,4 @@ class IVEReaderWriter : public ReaderWriter
 
 // now register with Registry to instantiate the above
 // reader/writer.
-RegisterReaderWriterProxy<IVEReaderWriter> g_IVEReaderWriterProxy;
+REGISTER_OSGPLUGIN(ive, ReaderWriterIVE)