Add osg_Viewport uniform to GLSL

osgviewport_uniform.diff

Index: src/osgUtil/SceneView.cpp
===================================================================
--- src/osgUtil/SceneView.cpp	(revision 13031)
+++ src/osgUtil/SceneView.cpp	(working copy)
@@ -424,6 +424,11 @@
         osg::Uniform* uniform = _localStateSet->getOrCreateUniform("osg_ViewMatrixInverse",osg::Uniform::FLOAT_MAT4);
         uniform->set(osg::Matrix::inverse(getViewMatrix()));
     }
+    if( _activeUniforms && getCamera() && getCamera()->getViewport() ) {
+        osg::Uniform* uniform = _localStateSet->getOrCreateUniform("osg_Viewport",osg::Uniform::FLOAT_VEC2);
+        osg::Viewport* v = getCamera()->getViewport();        
+        uniform->set( osg::Vec2( v->width(), v->height() ) );
+    }
 
 }