Implemented fade between layers using MultiTextureControl node

examples/osgmultitexturecontrol/CMakeLists.txt

@@ -1,4 +1,5 @@
 SET(TARGET_SRC osgmultitexturecontrol.cpp )
+SET(TARGET_ADDED_LIBRARIES osgFX )
 
 #### end var setup  ###
 SETUP_EXAMPLE(osgmultitexturecontrol )

examples/osgmultitexturecontrol/osgmultitexturecontrol.cpp

@@ -21,8 +21,7 @@
 #include <osg/Notify>
 
 #include <osg/Texture2D>
-#include <osg/TexEnv>
-#include <osg/TexGen>
+#include <osg/io_utils>
 
 #include <osgDB/Registry>
 #include <osgDB/ReadFile>
@@ -71,13 +70,112 @@ T* findTopMostNodeOfType(osg::Node* node)
     return fnotv._foundNode;
 }
 
+/** Callback used to track the elevation of the camera and update the texture weights in an MultiTextureControl node.*/
+class ElevationLayerBlendingCallback : public osg::NodeCallback
+{
+    public:
+    
+        typedef std::vector<double> Elevations;
+
+        ElevationLayerBlendingCallback(osgFX::MultiTextureControl* mtc, const Elevations& elevations, float animationTime=4.0f):
+            _previousFrame(-1),
+            _previousTime(0.0),
+            _mtc(mtc),
+            _elevations(elevations),
+            _animationTime(animationTime) {}
+    
+        /** Callback method called by the NodeVisitor when visiting a node.*/
+        virtual void operator()(osg::Node* node, osg::NodeVisitor* nv)
+        { 
+            if (!nv->getFrameStamp() || _previousFrame==nv->getFrameStamp()->getFrameNumber())
+            {
+                // we've already updated for this frame so no need to do it again, just traverse children.
+                traverse(node,nv);
+                return;
+            }
+            
+            float deltaTime = 0.01f;
+            if (_previousFrame!=-1)
+            {
+                deltaTime = float(nv->getFrameStamp()->getReferenceTime() - _previousTime);
+            }
+            
+            _previousTime = nv->getFrameStamp()->getReferenceTime();
+            _previousFrame = nv->getFrameStamp()->getFrameNumber();
+
+            double elevation = nv->getViewPoint().z();
+        
+            osg::CoordinateSystemNode* csn = dynamic_cast<osg::CoordinateSystemNode*>(node);
+            if (csn) 
+            {
+                osg::EllipsoidModel* em = csn->getEllipsoidModel();
+                if (em)
+                {
+                    double X = nv->getViewPoint().x();
+                    double Y = nv->getViewPoint().y();
+                    double Z = nv->getViewPoint().z();
+                    double latitude, longitude;
+                    em->convertXYZToLatLongHeight(X,Y,Z,latitude, longitude, elevation);
+                }
+            }
+        
+            if (_mtc.valid() && !_elevations.empty())
+            {
+                unsigned int index = _mtc->getNumTextureWeights()-1;
+                for(unsigned int i=0; i<_elevations.size(); ++i)
+                {
+                    if (elevation>_elevations[i]) 
+                    {
+                        index = i;
+                        break;
+                    }
+                }
+                
+                float delta = std::min(deltaTime/_animationTime, 1.0f);
+                
+                for(unsigned int i=0; i<_mtc->getNumTextureWeights(); ++i)
+                {
+                    float currentValue = _mtc->getTextureWeight(i);
+                    float desiredValue = (i==index) ? 1.0f : 0.0f;
+                    if (desiredValue != currentValue)
+                    {
+                        if (currentValue<desiredValue)
+                        {
+                            desiredValue = std::min(currentValue + delta, desiredValue);
+                        }
+                        else
+                        {
+                            desiredValue = std::max(currentValue - delta, desiredValue);
+                        }
+                    
+                        _mtc->setTextureWeight(i, desiredValue);
+                    }
+                }
+                
+            }
+        
+            traverse(node,nv);
+        }
+
+        int                                             _previousFrame;
+        double                                          _previousTime;
+        float                                           _animationTime;
+        osg::observer_ptr<osgFX::MultiTextureControl>   _mtc;
+        Elevations                                      _elevations;
+};
+
+
 int main( int argc, char **argv )
 {
     // use an ArgumentParser object to manage the program arguments.
     osg::ArgumentParser arguments(&argc,argv);
    
     // construct the viewer.
-    osgViewer::Viewer viewer;
+    osgViewer::Viewer viewer(arguments);
+
+    // quick hack to work around threading issue with osgFX::MultiTextureControl node's updating of
+    // its StateAttributes.
+    viewer.setThreadingModel(osgViewer::Viewer::SingleThreaded);
 
     // load the nodes from the commandline arguments.
     osg::Node* rootnode = osgDB::readNodeFiles(arguments);
@@ -89,16 +187,34 @@ int main( int argc, char **argv )
     }
     
     osg::CoordinateSystemNode* csn = findTopMostNodeOfType<osg::CoordinateSystemNode>(rootnode);
-    if (csn)
-    {
-        osg::notify(osg::NOTICE)<<"Found CSN"<<csn<<std::endl;
-    }
 
+    unsigned int numLayers = 1;
     osgFX::MultiTextureControl* mtc = findTopMostNodeOfType<osgFX::MultiTextureControl>(rootnode);
     if (mtc)
     {
-        osg::notify(osg::NOTICE)<<"Found MTC "<<mtc<<std::endl;
+        numLayers = mtc->getNumTextureWeights();
     }
+    
+    if (numLayers<2)
+    {
+        osg::notify(osg::NOTICE)<<"Warning: scene must have MultiTextureControl node with at least 2 texture units defined."<<std::endl;
+        return 1;
+    }
+    
+    double maxElevationTransition = 1e6;
+    ElevationLayerBlendingCallback::Elevations elevations;
+    for(unsigned int i=0; i<numLayers; ++i)
+    {
+        elevations.push_back(maxElevationTransition);
+        maxElevationTransition /= 2.0;
+    }
+    
+    ElevationLayerBlendingCallback* elbc = new ElevationLayerBlendingCallback(mtc, elevations);
+
+    // assign to the most appropriate node (the CoordinateSystemNode is best as it provides the elevation on the globe.)
+    if (csn) csn->setCullCallback(elbc);    
+    else if (mtc) mtc->setCullCallback(elbc);
+    else rootnode->setCullCallback(elbc);
 
     // add terrain manipulator
     viewer.setCameraManipulator(new osgGA::TerrainManipulator);