Made the image view objects implement the generic image interface. Not sure

why I didn't do this a long time ago.

dlib/image_processing/generic_image.h

@@ -293,6 +293,8 @@ namespace dlib
                 - sets the image to have 0 pixels in it.
         !*/
 
+        long get_width_step() const { return _width_step; }
+
     private:
 
         char* _data;
@@ -362,6 +364,8 @@ namespace dlib
         }
 #endif
 
+        long get_width_step() const { return _width_step; }
+
     private:
         const char* _data;
         long _width_step;
@@ -393,6 +397,14 @@ namespace dlib
             - constructs a const_image_view from an image object
     !*/
 
+
+    // Don't stack image views on image views since that's pointless and just slows the
+    // compilation.
+    template <typename T> image_view<T>&             make_image_view ( image_view<T>& img)             { return img; }
+    template <typename T> const image_view<T>&       make_image_view ( const image_view<T>& img)       { return img; }
+    template <typename T> const_image_view<T>&       make_image_view ( const_image_view<T>& img)       { return img; }
+    template <typename T> const const_image_view<T>& make_image_view ( const const_image_view<T>& img) { return img; }
+
 // ----------------------------------------------------------------------------------------
 
     template <typename image_type>
@@ -431,6 +443,86 @@ namespace dlib
               objects should provide their own overload of num_rows() if needed.
     !*/
 
+// ----------------------------------------------------------------------------------------
+// ----------------------------------------------------------------------------------------
+//            Make the image views implement the generic image interface
+// ----------------------------------------------------------------------------------------
+// ----------------------------------------------------------------------------------------
+
+    template <typename T>
+    struct image_traits<image_view<T>>
+    {
+        typedef typename image_traits<T>::pixel_type pixel_type;
+    };
+    template <typename T>
+    struct image_traits<const image_view<T>>
+    {
+        typedef typename image_traits<T>::pixel_type pixel_type;
+    };
+
+    template <typename T>
+    inline long num_rows( const image_view<T>& img) { return img.nr(); }
+    template <typename T>
+    inline long num_columns( const image_view<T>& img) { return img.nc(); }
+
+    template <typename T>
+    inline void set_image_size( image_view<T>& img, long rows, long cols ) { img.set_size(rows,cols); }
+
+    template <typename T>
+    inline void* image_data( image_view<T>& img)
+    {
+        if (img.size() != 0)
+            return &img[0][0];
+        else
+            return 0;
+    }
+
+    template <typename T>
+    inline const void* image_data(
+        const image_view<T>& img
+    )
+    {
+        if (img.size() != 0)
+            return &img[0][0];
+        else
+            return 0;
+    }
+
+    template <typename T>
+    inline long width_step( const image_view<T>& img) { return img.get_width_step(); }
+
+// ----------------------------------------------------------------------------------------
+
+    template <typename T>
+    struct image_traits<const_image_view<T>>
+    {
+        typedef typename image_traits<T>::pixel_type pixel_type;
+    };
+    template <typename T>
+    struct image_traits<const const_image_view<T>>
+    {
+        typedef typename image_traits<T>::pixel_type pixel_type;
+    };
+
+    template <typename T>
+    inline long num_rows( const const_image_view<T>& img) { return img.nr(); }
+    template <typename T>
+    inline long num_columns( const const_image_view<T>& img) { return img.nc(); }
+
+    template <typename T>
+    inline const void* image_data(
+        const const_image_view<T>& img
+    )
+    {
+        if (img.size() != 0)
+            return &img[0][0];
+        else
+            return 0;
+    }
+
+    template <typename T>
+    inline long width_step( const const_image_view<T>& img) { return img.get_width_step(); }
+
 // ----------------------------------------------------------------------------------------
 
 }