Aded extra constructors to BlendFunc and Depth to help set them up convieniently.

Added a background quad to osghud.

src/osg/Depth.cpp

@@ -14,16 +14,14 @@
 
 using namespace osg;
 
-Depth::Depth()
+Depth::Depth(Function func,double zNear, double zFar,bool writeMask):
+    _func(func),
+    _zNear(zNear),
+    _zFar(zFar),
+    _depthWriteMask(writeMask)
 {
-    _func = LESS;
-    _depthWriteMask = true;
-
-    _zNear = 0.0;
-    _zFar = 1.0;
 }
 
-
 Depth::~Depth()
 {
 }
@@ -31,7 +29,7 @@ Depth::~Depth()
 void Depth::apply(State&) const
 {
     glDepthFunc((GLenum)_func);
-    glDepthMask((GLboolean)_depthWriteMask);
     glDepthRange(_zNear,_zFar);
+    glDepthMask((GLboolean)_depthWriteMask);
 }