Rework gtk3 window resize and draw cleanup

The gtk3 resize functions fail to shrink the window after it has been
resized. This edit changes this and allows the window to be shrunk
back to its original size.

This edit also cleans up the draw/expose functions.

modules/highgui/src/window_gtk.cpp

@@ -232,6 +232,56 @@ static CvSize cvImageWidget_calc_size( int im_width, int im_height, int max_widt
     return cvSize( cvRound(max_height*aspect), max_height );
 }
 
+#if defined (HAVE_GTK3)
+static void
+cvImageWidget_get_preferred_width (GtkWidget *widget, gint *minimal_width, gint *natural_width)
+{
+  g_return_if_fail (widget != NULL);
+  g_return_if_fail (CV_IS_IMAGE_WIDGET (widget));
+  CvImageWidget * image_widget = CV_IMAGE_WIDGET( widget );
+
+  if(image_widget->original_image != NULL) {
+    *minimal_width = image_widget->flags & CV_WINDOW_AUTOSIZE ?
+      gdk_window_get_width(gtk_widget_get_window(widget)) : image_widget->original_image->cols;
+  }
+  else {
+    *minimal_width = 320;
+  }
+
+  if(image_widget->scaled_image != NULL) {
+    *natural_width = *minimal_width < image_widget->scaled_image->cols ?
+      image_widget->scaled_image->cols : *minimal_width;
+  }
+  else {
+    *natural_width = *minimal_width;
+  }
+}
+
+static void
+cvImageWidget_get_preferred_height (GtkWidget *widget, gint *minimal_height, gint *natural_height)
+{
+  g_return_if_fail (widget != NULL);
+  g_return_if_fail (CV_IS_IMAGE_WIDGET (widget));
+  CvImageWidget * image_widget = CV_IMAGE_WIDGET( widget );
+
+  if(image_widget->original_image != NULL) {
+    *minimal_height = image_widget->flags & CV_WINDOW_AUTOSIZE ?
+      gdk_window_get_height(gtk_widget_get_window(widget)) : image_widget->original_image->rows;
+  }
+  else {
+    *minimal_height = 240;
+  }
+
+  if(image_widget->scaled_image != NULL) {
+    *natural_height = *minimal_height < image_widget->scaled_image->rows ?
+      image_widget->scaled_image->cols : *minimal_height;
+  }
+  else {
+    *natural_height = *minimal_height;
+  }
+}
+
+#else
 static void
 cvImageWidget_size_request (GtkWidget      *widget,
                        GtkRequisition *requisition)
@@ -262,25 +312,6 @@ cvImageWidget_size_request (GtkWidget      *widget,
     }
     //printf("%d %d\n",requisition->width, requisition->height);
 }
-
-#if defined (HAVE_GTK3)
-static void
-cvImageWidget_get_preferred_width (GtkWidget *widget, gint *minimal_width, gint *natural_width)
-{
-  GtkRequisition requisition;
-
-  cvImageWidget_size_request (widget, &requisition);
-  *minimal_width = *natural_width = requisition.width;
-}
-
-static void
-cvImageWidget_get_preferred_height (GtkWidget *widget, gint *minimal_height, gint *natural_height)
-{
-  GtkRequisition requisition;
-
-  cvImageWidget_size_request (widget, &requisition);
-  *minimal_height = *natural_height = requisition.height;
-}
 #endif //HAVE_GTK3
 
 static void cvImageWidget_set_size(GtkWidget * widget, int max_width, int max_height){
@@ -860,7 +891,6 @@ static gboolean cvImageWidget_draw(GtkWidget* widget, cairo_t *cr, gpointer data
   g_return_val_if_fail (widget != NULL, FALSE);
   g_return_val_if_fail (CV_IS_IMAGE_WIDGET (widget), FALSE);
 
-  cr = gdk_cairo_create(gtk_widget_get_window(widget));
   image_widget = CV_IMAGE_WIDGET (widget);
 
   if( image_widget->scaled_image ){
@@ -884,7 +914,7 @@ static gboolean cvImageWidget_draw(GtkWidget* widget, cairo_t *cr, gpointer data
   }
 
   cairo_paint(cr);
-  cairo_destroy(cr);
+  g_object_unref(pixbuf);
   return TRUE;
 }
 
@@ -938,6 +968,7 @@ static gboolean cvImageWidget_expose(GtkWidget* widget, GdkEventExpose* event, g
   }
 
   cairo_paint(cr);
+  g_object_unref(pixbuf);
   cairo_destroy(cr);
   return TRUE;
 }