Added osg::Image::dirtyImage() and setModifiedTag() to allow external

updating of the image modified flag to be used in conjunction with
texture subloading.

include/osg/Image

@@ -69,7 +69,13 @@ class SG_EXPORT Image : public Object
           */
         void ensureDimensionsArePowerOfTwo();
       
-        /** Get modified tag value. */
+        /** Dirty the image, which increments the modified flag, to force osg::Texture to reload the image.*/
+        inline void dirtyImage() { ++_modifiedTag; }      
+      
+        /** Set the modified tag value, only used by osg::Texture when using texture subloading. */
+        inline void setModifiedTag(const unsigned int value) { _modifiedTag=value; }
+
+        /** Get modified tag value, only used by osg::Texture when using texture subloading. */
         inline const unsigned int getModifiedTag() const { return _modifiedTag; }
 
     protected :

src/osg/Image.cpp

@@ -22,6 +22,8 @@ Image::Image()
     _packing         = 4;
 
     _data = (unsigned char *)0L;
+
+    _modifiedTag = 0;
 }
 
 
@@ -68,6 +70,8 @@ void Image::setImage(const int s,const int t,const int r,
 
     // test scaling...
     //    scaleImageTo(16,16,_r);
+    
+    ++_modifiedTag;
 
 }
 
@@ -106,6 +110,8 @@ void Image::scaleImage(const int s,const int t,const int /*r*/)
 
         notify(WARN) << "Error Image::scaleImage() do not succeed : errorString = "<<gluErrorString((GLenum)status)<<endl;
     }
+    
+    ++_modifiedTag;
 }