Slightly more efficient applying of light state

components/sceneutil/lightmanager.cpp

@@ -45,6 +45,8 @@ namespace SceneUtil
 
         virtual void apply(osg::State& state) const
         {
+            if (mLights.empty())
+                return;
             osg::Matrix modelViewMatrix = state.getModelViewMatrix();
 
             state.applyModelViewMatrix(state.getInitialViewMatrix());
@@ -193,16 +195,25 @@ namespace SceneUtil
         else
         {
             osg::ref_ptr<osg::StateSet> stateset = new osg::StateSet;
-
+            std::vector<osg::ref_ptr<osg::Light> > lights;
             for (unsigned int i=0; i<lightList.size();++i)
             {
-                std::vector<osg::ref_ptr<osg::Light> > lights;
                 lights.push_back(lightList[i]->mLightSource->getLight(frameNum));
-                osg::ref_ptr<LightStateAttribute> attr = new LightStateAttribute(mStartLight+i, lights);
-                // don't use setAttributeAndModes, that does not support light indices!
-                stateset->setAttribute(attr, osg::StateAttribute::ON);
-                stateset->setAssociatedModes(attr, osg::StateAttribute::ON);
+            }
 
+            // the first light state attribute handles the actual state setting for all lights
+            // it's best to batch these up so that we don't need to touch the modelView matrix more than necessary
+            osg::ref_ptr<LightStateAttribute> attr = new LightStateAttribute(mStartLight, lights);
+            // don't use setAttributeAndModes, that does not support light indices!
+            stateset->setAttribute(attr, osg::StateAttribute::ON);
+            stateset->setAssociatedModes(attr, osg::StateAttribute::ON);
+
+            // need to push some dummy attributes to ensure proper state tracking
+            // lights need to reset to their default when the StateSet is popped
+            for (unsigned int i=1; i<lightList.size(); ++i)
+            {
+                osg::ref_ptr<LightStateAttribute> dummy = new LightStateAttribute(mStartLight+i, std::vector<osg::ref_ptr<osg::Light> >());
+                stateset->setAttribute(dummy, osg::StateAttribute::ON);
             }
 
             stateSetCache.insert(std::make_pair(hash, stateset));