Changed the image_window so that it doesn't resize itself if you keep

giving it images that are the same size.  This way if you are sending
video data to it will allow the user to change the size of the window
without having it snap right back.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%403181

dlib/gui_widgets/widgets.cpp

@@ -5806,7 +5806,9 @@ namespace dlib
     image_window::
     image_window(
     ) :
-        gui_img(*this)
+        gui_img(*this),
+        nr(0),
+        nc(0)
     {
         // show this window on the screen
         show();

dlib/gui_widgets/widgets.h

@@ -3077,8 +3077,15 @@ namespace dlib
         )
         {
             auto_mutex M(m);
+
+            // if the new image has a different size when compared to the previous image
+            // then we should readjust the total rectangle size.
+            if (new_img.nr() != img.nr() || new_img.nc() != img.nc())
+                set_total_rect_size(new_img.nc(), new_img.nr());
+            else
+                parent.invalidate_rectangle(rect);
+
             assign_image(img,new_img);
-            set_total_rect_size(img.nc(), img.nr());
         }
 
         struct overlay_rect
@@ -3162,7 +3169,7 @@ namespace dlib
         template < typename image_type >
         image_window(
             const image_type& img
-        ) : gui_img(*this) { set_image(img); show(); }
+        ) : gui_img(*this), nr(0), nc(0) { set_image(img); show(); }
 
         ~image_window(
         );
@@ -3176,11 +3183,19 @@ namespace dlib
             auto_mutex M(wm);
             gui_img.set_image(img); 
 
-            // set the size of this window to match the size of the input image
-            set_size(img.nc()+padding*2,img.nr()+padding*2);
+            // Only readjust the size of the window if the new image has a different size
+            // than the last image given to this object.
+            if (img.nr() != nr || img.nc() != nc)
+            {
+                // set the size of this window to match the size of the input image
+                set_size(img.nc()+padding*2,img.nr()+padding*2);
+
+                // call this to make sure everything else is setup properly
+                on_window_resized();
 
-            // call this to make sure everything else is setup properly
-            on_window_resized();
+                nr = img.nr();
+                nc = img.nc();
+            }
         }
 
         void add_overlay (
@@ -3212,6 +3227,7 @@ namespace dlib
         image_window& operator= (image_window&);
 
         image_display gui_img;
+        long nr, nc;
     };
 
 // ----------------------------------------------------------------------------------------