Updates to Shape support.

src/osg/Shape.cpp

@@ -41,3 +41,41 @@ void Grid::populateGrid(float minValue,float maxValue)
 	}
     }
 }
+
+Vec3 HeightField::getNormal(unsigned int c,unsigned int r) const 
+{
+    // four point normal generation.
+
+    float dz_dx;
+    if (c==0)
+    {
+    	dz_dx = (getHeight(c+1,r)-getHeight(c,r))/getXInterval();
+    }
+    else if (c==getNumColumns()-1)
+    {
+    	dz_dx = (getHeight(c,r)-getHeight(c-1,r))/getXInterval();
+    }
+    else // assume 0<c<_numColumns-1
+    {
+    	dz_dx = 0.5f*(getHeight(c+1,r)-getHeight(c-1,r))/getXInterval();
+    }
+    
+    float dz_dy;
+    if (r==0)
+    {
+    	dz_dy = (getHeight(c,r+1)-getHeight(c,r))/getYInterval();
+    }
+    else if (r==getNumRows()-1)
+    {
+    	dz_dy = (getHeight(c,r)-getHeight(c,r-1))/getYInterval();
+    }
+    else // assume 0<r<_numRows-1
+    {
+    	dz_dy = 0.5f*(getHeight(c,r+1)-getHeight(c,r-1))/getYInterval();
+    }
+    
+    Vec3 normal(-dz_dx,-dz_dy,1.0f);
+    normal.normalize();
+    
+    return normal;
+}