Further work on improving stereo support in the OSG.

Renamed the osg::VisualsSettings to osg::DisplaySettings, and
osgUtil::VisualsRequirementsVisitor to osgUtil::DisplayRequirementsVisitor.

Added support for OSG_SCREEN_HEIGHT into osg::DisplaySettings, and added
a DisplaySettings* to the constructors of osg::SceneView and osg::Camera.

src/osgUtil/DisplayRequirementsVisitor.cpp

@@ -0,0 +1,76 @@
+#if defined(_MSC_VER)
+	#pragma warning( disable : 4786 )
+#endif
+
+#include <stdio.h>
+#include <list>
+#include <set>
+
+#include <osg/GeoSet>
+
+#include <osgUtil/DisplayRequirementsVisitor>
+
+using namespace osg;
+using namespace osgUtil;
+
+DisplayRequirementsVisitor::DisplayRequirementsVisitor()
+{
+    setTraversalMode(NodeVisitor::TRAVERSE_ALL_CHILDREN);
+}
+
+void DisplayRequirementsVisitor::applyStateSet(StateSet& stateset)
+{
+    if (!_ds) _ds = new osg::DisplaySettings;
+
+   unsigned int min = 0; // assume stencil not needed by this stateset.
+   
+   if (stateset.getMode(GL_STENCIL_TEST) & StateAttribute::ON)
+   {
+        min = 1; // number stencil bits we need at least.
+   }
+
+   if (stateset.getAttribute(StateAttribute::STENCIL))
+   {
+        min = 1; // number stencil bits we need at least.
+   }
+   
+   if (min>_ds->getMinimumNumStencilBits())
+   {
+        // only update if new minimum exceeds previous minimum.
+        _ds->setMinimumNumStencilBits(min);
+   }    
+}
+
+void DisplayRequirementsVisitor::apply(Node& node)
+{
+    osg::StateSet* stateset = node.getStateSet();
+    if (stateset) applyStateSet(*stateset);
+
+    traverse(node);
+}
+
+void DisplayRequirementsVisitor::apply(Geode& geode)
+{
+    osg::StateSet* geode_stateset = geode.getStateSet();
+    if (geode_stateset) applyStateSet(*geode_stateset);
+    
+    for(int i = 0; i < geode.getNumDrawables(); i++ )
+    {
+        osg::StateSet* stateset = geode.getDrawable(i)->getStateSet();
+        if (stateset) applyStateSet(*stateset);
+    }
+}
+
+void DisplayRequirementsVisitor::apply(Impostor& impostor)
+{
+    if (!_ds) _ds = new osg::DisplaySettings;
+
+    unsigned int min = 1; // number alpha bits we need at least.
+    if (min>_ds->getMinimumNumAlphaBits())
+    {
+        // only update if new minimum exceeds previous minimum.
+        _ds->setMinimumNumAlphaBits(min);
+    }
+    
+    apply((Node&)impostor);
+}