From John Kaniarz, "Here is an example of using tessellation shaders in osg. With permission from the author, I adapted it from this tutorial:

http://prideout.net/blog/?p=48"

examples/CMakeLists.txt

@@ -176,6 +176,7 @@ IF(DYNAMIC_OPENSCENEGRAPH)
 
     ADD_SUBDIRECTORY(osgphotoalbum)
     ADD_SUBDIRECTORY(osgtessellate)
+    ADD_SUBDIRECTORY(osgtessellationshaders)
 
     ADD_SUBDIRECTORY(osgpdf)
 

examples/osgtessellationshaders/CMakeLists.txt

@@ -0,0 +1,2 @@
+SET(TARGET_SRC osgtessellationshaders.cpp )
+SETUP_EXAMPLE(osgtessellationshaders)

examples/osgtessellationshaders/osgtessellationshaders.cpp

@@ -0,0 +1,247 @@
+/* A demonstration of Tessellation Shaders in OpenScenegraph.
+ * Original code by Philip Rideout
+ * Adapted to OpenScenegraph by John Kaniarz
+ */
+
+#include <osg/Program>
+#include <osg/ShapeDrawable>
+#include <osgViewer/Viewer>
+#include <osgViewer/ViewerEventHandlers>
+#include <osgGA/TrackballManipulator>
+
+static const char* vertSource = {
+"#version 400\n"
+"in vec4 osg_Vertex;\n"
+"out vec3 vPosition;\n"
+"void main(){\n"
+"	vPosition = osg_Vertex.xyz;\n"
+"}\n"
+};
+static const char* tessControlSource = {
+"#version 400\n"
+"layout(vertices = 3) out;\n"
+"in vec3 vPosition[];\n"
+"out vec3 tcPosition[];\n"
+"uniform float TessLevelInner;\n"
+"uniform float TessLevelOuter;\n"
+"#define ID gl_InvocationID\n"
+"void main(){\n"
+"    tcPosition[ID] = vPosition[ID];\n"
+"    if (ID == 0) {\n"
+"        gl_TessLevelInner[0] = TessLevelInner;\n"
+"        gl_TessLevelOuter[0] = TessLevelOuter;\n"
+"        gl_TessLevelOuter[1] = TessLevelOuter;\n"
+"        gl_TessLevelOuter[2] = TessLevelOuter;\n"
+"    }\n"
+"}\n"
+};
+static const char* tessEvalSource = {
+"#version 400\n"
+"layout(triangles, equal_spacing, cw) in;\n"
+"in vec3 tcPosition[];\n"
+"out vec3 tePosition;\n"
+"out vec3 tePatchDistance;\n"
+"uniform mat4 osg_ProjectionMatrix;\n"
+"uniform mat4 osg_ModelViewMatrix;\n"
+"void main(){\n"
+"    vec3 p0 = gl_TessCoord.x * tcPosition[0];\n"
+"    vec3 p1 = gl_TessCoord.y * tcPosition[1];\n"
+"    vec3 p2 = gl_TessCoord.z * tcPosition[2];\n"
+"    tePatchDistance = gl_TessCoord;\n"
+"    tePosition = normalize(p0 + p1 + p2);\n"
+"    gl_Position = osg_ProjectionMatrix * osg_ModelViewMatrix * vec4(tePosition, 1);\n"
+"}\n"
+};
+static const char* geomSource = {
+"#version 400\n"
+"uniform mat4 osg_ModelViewMatrix;\n"
+"uniform mat3 osg_NormalMatrix;\n"
+"layout(triangles) in;\n"
+"layout(triangle_strip, max_vertices = 3) out;\n"
+"in vec3 tePosition[3];\n"
+"in vec3 tePatchDistance[3];\n"
+"out vec3 gFacetNormal;\n"
+"out vec3 gPatchDistance;\n"
+"out vec3 gTriDistance;\n"
+"out vec4 gColor;\n"
+"void main(){\n"
+"    vec3 A = tePosition[2] - tePosition[0];\n"
+"    vec3 B = tePosition[1] - tePosition[0];\n"
+"    gFacetNormal = osg_NormalMatrix * normalize(cross(A, B));\n"
+"    gPatchDistance = tePatchDistance[0];\n"
+"    gTriDistance = vec3(1, 0, 0);\n"
+"    gColor = osg_ModelViewMatrix[0];\n"
+"    gl_Position = gl_in[0].gl_Position; EmitVertex();\n"
+"    gPatchDistance = tePatchDistance[1];\n"
+"    gTriDistance = vec3(0, 1, 0);\n"
+"    gColor = osg_ModelViewMatrix[1];\n"
+"    gl_Position = gl_in[1].gl_Position; EmitVertex();\n"
+"    gPatchDistance = tePatchDistance[2];\n"
+"    gTriDistance = vec3(0, 0, 1);\n"
+"    gColor = osg_ModelViewMatrix[2];\n"
+"    gl_Position = gl_in[2].gl_Position; EmitVertex();\n"
+"    EndPrimitive();\n"
+"}\n"
+};
+static const char* fragSource = {
+"#version 400\n"
+"out vec4 FragColor;\n"
+"in vec3 gFacetNormal;\n"
+"in vec3 gTriDistance;\n"
+"in vec3 gPatchDistance;\n"
+"in vec4 gColor;\n"
+"in float gPrimitive;\n"
+"uniform vec3 LightPosition;\n"
+"uniform vec3 DiffuseMaterial;\n"
+"uniform vec3 AmbientMaterial;\n"
+"float amplify(float d, float scale, float offset){\n"
+"    d = scale * d + offset;\n"
+"    d = clamp(d, 0, 1);\n"
+"    d = 1 - exp2(-2*d*d);\n"
+"    return d;\n"
+"}\n"
+"void main(){\n"
+"    vec3 N = normalize(gFacetNormal);\n"
+"    vec3 L = LightPosition;\n"
+"    float df = abs(dot(N, L));\n"
+"    vec3 color = AmbientMaterial + df * DiffuseMaterial;\n"
+"    float d1 = min(min(gTriDistance.x, gTriDistance.y), gTriDistance.z);\n"
+"    float d2 = min(min(gPatchDistance.x, gPatchDistance.y), gPatchDistance.z);\n"
+"    color = amplify(d1, 40, -0.5) * amplify(d2, 60, -0.5) * color;\n"
+"    FragColor = vec4(color, 1.0);\n"
+"}\n"
+};
+
+osg::ref_ptr<osg::Geode> CreateIcosahedron(osg::Program *program){
+	osg::Geode *geode=new osg::Geode();
+	osg::Geometry *geometry = new osg::Geometry();
+	const unsigned int Faces[] = {
+        2, 1, 0,
+        3, 2, 0,
+        4, 3, 0,
+        5, 4, 0,
+        1, 5, 0,
+
+        11, 6,  7,
+        11, 7,  8,
+        11, 8,  9,
+        11, 9,  10,
+        11, 10, 6,
+
+        1, 2, 6,
+        2, 3, 7,
+        3, 4, 8,
+        4, 5, 9,
+        5, 1, 10,
+
+        2,  7, 6,
+        3,  8, 7,
+        4,  9, 8,
+        5, 10, 9,
+        1, 6, 10 };
+	int IndexCount = sizeof(Faces) / sizeof(Faces[0]);
+    const float Verts[] = {
+         0.000f,  0.000f,  1.000f,
+         0.894f,  0.000f,  0.447f,
+         0.276f,  0.851f,  0.447f,
+        -0.724f,  0.526f,  0.447f,
+        -0.724f, -0.526f,  0.447f,
+         0.276f, -0.851f,  0.447f,
+         0.724f,  0.526f, -0.447f,
+        -0.276f,  0.851f, -0.447f,
+        -0.894f,  0.000f, -0.447f,
+        -0.276f, -0.851f, -0.447f,
+         0.724f, -0.526f, -0.447f,
+         0.000f,  0.000f, -1.000f };
+
+    int VertexCount = sizeof(Verts)/sizeof(float);
+	osg::Vec3Array* vertices = new osg::Vec3Array();
+	for(int i=0;i<VertexCount;i+=3){
+		vertices->push_back(osg::Vec3(Verts[i],Verts[i+1],Verts[i+2]));
+	}
+	geometry->setVertexArray(vertices);
+	geometry->addPrimitiveSet(new osg::DrawElementsUInt(osg::PrimitiveSet::PATCHES,IndexCount,Faces));
+
+	geode->addDrawable(geometry);
+	return geode;
+}
+osg::ref_ptr<osg::Program> createProgram(){
+	osg::Program *program = new osg::Program();
+	program->addShader(new osg::Shader(osg::Shader::VERTEX,vertSource));
+	program->addShader(new osg::Shader(osg::Shader::TESSCONTROL,tessControlSource));
+	program->addShader(new osg::Shader(osg::Shader::TESSEVALUATION,tessEvalSource));
+	program->addShader(new osg::Shader(osg::Shader::GEOMETRY,geomSource));
+	program->addShader(new osg::Shader(osg::Shader::FRAGMENT,fragSource));
+	program->setParameter(GL_GEOMETRY_VERTICES_OUT_EXT, 3);
+	program->setParameter(GL_GEOMETRY_INPUT_TYPE_EXT, GL_TRIANGLES);
+	program->setParameter(GL_GEOMETRY_OUTPUT_TYPE_EXT, GL_TRIANGLE_STRIP);
+	program->setParameter(GL_PATCH_VERTICES,3);
+	return program;
+}
+
+float tessInner=1.0f;
+float tessOuter=1.0f;
+osg::ref_ptr<osg::Uniform> tessInnerU = new osg::Uniform("TessLevelInner",tessInner);
+osg::ref_ptr<osg::Uniform> tessOuterU = new osg::Uniform("TessLevelOuter",tessOuter);
+
+class KeyboardEventHandler : public osgGA::GUIEventHandler {
+public:
+	KeyboardEventHandler():osgGA::GUIEventHandler(){}
+	virtual bool handle(const osgGA::GUIEventAdapter& ea,osgGA::GUIActionAdapter& gaa){
+		if(ea.getEventType()==osgGA::GUIEventAdapter::KEYDOWN){
+			switch (ea.getKey()){
+				case osgGA::GUIEventAdapter::KEY_Up:
+					tessOuter++;
+					tessOuterU->set(tessOuter);
+					return true;
+				case osgGA::GUIEventAdapter::KEY_Down:
+					tessOuter--;
+					tessOuter=std::max(1.0f,tessOuter);
+					tessOuterU->set(tessOuter);
+					return true;
+				case osgGA::GUIEventAdapter::KEY_Left:
+					tessInner--;
+					tessInner=std::max(1.0f,tessInner);
+					tessInnerU->set(tessInner);
+					return true;
+				case osgGA::GUIEventAdapter::KEY_Right:
+					tessInner++;
+					tessInnerU->set(tessInner);
+					return true;
+			}
+		}
+		return osgGA::GUIEventHandler::handle(ea,gaa);
+	}
+};
+int main(int argc, char* argv[])
+{
+	osgViewer::Viewer viewer;
+	viewer.setUpViewInWindow(100,100,800,600);
+	osg::ref_ptr<osg::Program> program = createProgram();
+	osg::ref_ptr<osg::Geode> geode = CreateIcosahedron(program.get());
+	osg::StateSet *state;
+	state = geode->getOrCreateStateSet();
+	state->addUniform(new osg::Uniform("AmbientMaterial",osg::Vec3(0.04f, 0.04f, 0.04f)));
+	state->addUniform(new osg::Uniform("DiffuseMaterial",osg::Vec3(0.0f, 0.75f, 0.75f)));
+	state->addUniform(new osg::Uniform("LightPosition",osg::Vec3(0.25f, 0.25f, 1.0f)));
+	state->addUniform(tessInnerU.get());
+	state->addUniform(tessOuterU.get());
+	state->setAttribute(program.get());
+    
+	// switch on the uniforms that track the modelview and projection matrices
+    osgViewer::Viewer::Windows windows;
+    viewer.getWindows(windows);
+    for(osgViewer::Viewer::Windows::iterator itr = windows.begin();
+        itr != windows.end();
+        ++itr)
+    {
+		osg::State *s=(*itr)->getState();
+        s->setUseModelViewAndProjectionUniforms(true);
+		s->setUseVertexAttributeAliasing(true);
+    }
+	
+	viewer.addEventHandler(new KeyboardEventHandler());
+	viewer.setSceneData(geode.get());
+	return viewer.run();
+}
+