From Ulrich Hertlein, "attached is a stencil buffer-based constant-width outline f/x with example. I've also modified osgfxbrowser to setup the stencil buffer accordingly."

include/osgFX/Outline

@@ -0,0 +1,97 @@
+// -*-c++-*-
+
+/*
+ * OpenSceneGraph - Copyright (C) 1998-2009 Robert Osfield
+ *
+ * This library is open source and may be redistributed and/or modified under
+ * the terms of the OpenSceneGraph Public License (OSGPL) version 0.0 or
+ * (at your option) any later version.  The full license is in LICENSE file
+ * included with this distribution, and on the openscenegraph.org website.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * OpenSceneGraph Public License for more details.
+ */
+
+/*
+ * osgFX::Outline - Copyright (C) 2004,2009 Ulrich Hertlein
+ */
+
+#ifndef OSGFX_OUTLINE_
+#define OSGFX_OUTLINE_
+
+#include <osgFX/Export>
+#include <osgFX/Effect>
+
+namespace osgFX
+{
+    /**
+     * Outline effect.
+     * This effect draws a stencil buffer-based outline around an object.
+     * Color and width of the outline can be modified.
+     * To function correctly the context must be setup with a stencil buffer
+     * and the stencil buffer must be cleared to zero before each render.
+     *
+     * osg::DisplaySettings::instance()->setMinimumNumStencilBits(1);
+     * camera->setClearMask(clearMask | GL_STENCIL_BUFFER_BIT);
+     * camera->setClearStencil(0);
+     */
+    class Outline : public Effect
+    {
+    public:
+        /// Constructor.
+        Outline();
+
+        /// Copy constructor.
+        Outline(const Outline& copy, const osg::CopyOp& op = osg::CopyOp::SHALLOW_COPY) : Effect(copy, op) {
+            _width = copy._width;
+            _color = copy._color;
+            _technique = copy._technique;
+        }
+
+        // Effect class info
+        META_Effect(osgFX, Outline, "Outline",
+                    "Stencil buffer based object outline effect.\n"
+                    "This effect needs a properly setup stencil buffer.",
+                    "Ulrich Hertlein <u.hertlein@sandbox.de>");
+
+        /// Set outline width.
+        void setWidth(float w);
+
+        /// Get outline width.
+        float getWidth() const {
+            return _width;
+        }
+
+        /// Set outline color.
+        void setColor(const osg::Vec4& color);
+
+        /// Get outline color.
+        const osg::Vec4& getColor() const {
+            return _color;
+        }
+
+    protected:
+        /// Destructor.
+        virtual ~Outline() {
+        }
+
+        /// Define available techniques.
+        bool define_techniques();
+
+    private:
+        /// Outline width.
+        float _width;
+
+        /// Outline color.
+        osg::Vec4 _color;
+
+        /// Technique.
+        class OutlineTechnique;
+        OutlineTechnique* _technique;
+    };
+
+}
+
+#endif