Ensure shader requirements are pushed at least once for subgraph

Shaders, if deemed necessary, get attached to the node mentioned by the
top of the requirements stack. Previously an empty stack was incorrectly
assumed to mean no shaders were required, but we found out that was
wrong. We need to put shaders *somewhere*, and the root of the subgraph
we're modifying should be the best place.

components/shader/shadervisitor.cpp

@@ -212,15 +212,17 @@ namespace Shader
 
     void ShaderVisitor::apply(osg::Node& node)
     {
-        if (node.getStateSet())
+        bool needPop = false;
+        if (node.getStateSet() || mRequirements.empty())
         {
+            needPop = true;
             pushRequirements(node);
+            if (node.getStateSet())
                 applyStateSet(node.getStateSet(), node);
-            traverse(node);
-            popRequirements();
         }
-        else
         traverse(node);
+        if (needPop)
+            popRequirements();
     }
 
     osg::StateSet* getWritableStateSet(osg::Node& node)
@@ -865,12 +867,12 @@ namespace Shader
 
     void ShaderVisitor::apply(osg::Geometry& geometry)
     {
-        bool needPop = (geometry.getStateSet() != nullptr);
-        if (geometry.getStateSet()) // TODO: check if stateset affects shader permutation before pushing it
-        {
+        bool needPop = geometry.getStateSet() || mRequirements.empty();
+        if (needPop)
             pushRequirements(geometry);
+
+        if (geometry.getStateSet()) // TODO: check if stateset affects shader permutation before pushing it
             applyStateSet(geometry.getStateSet(), geometry);
-        }
 
         if (!mRequirements.empty())
         {
@@ -889,7 +891,7 @@ namespace Shader
 
     void ShaderVisitor::apply(osg::Drawable& drawable)
     {
-        bool needPop = drawable.getStateSet();
+        bool needPop = drawable.getStateSet() || mRequirements.empty();
 
         if (needPop)
         {
@@ -899,8 +901,6 @@ namespace Shader
                 applyStateSet(drawable.getStateSet(), drawable);
         }
 
-        if (!mRequirements.empty())
-        {
         const ShaderRequirements& reqs = mRequirements.back();
         createProgram(reqs);
 
@@ -926,9 +926,6 @@ namespace Shader
                 osgaRig->setSourceRigGeometry(sourceOsgaRigGeometry);
             }
         }
-        }
-        else
-            ensureFFP(drawable);
 
         if (needPop)
             popRequirements();