fix mousewheel scrolling

... don't set DISCRETE fixes it

Author: jcupitt

README.md

@@ -133,12 +133,6 @@ $ vipsdisp ~/pics/k2.jpg
 - gtk 4.10 added GSK_SCALING_FILTER_NEAREST and GskTextureScale ... use this
   for the main window
 
-- looks like we need our own scrolledwindow
-
-    https://discourse.gnome.org/t/scrolledwindow-and-image-view-apps/15101
-
-  copy-paste the gtk one and remove the mousewheel scroll code
-
 - fix deprecation warnings
 
     at least hide them!

src/imagewindow.c

@@ -1306,7 +1306,6 @@ image_window_init( ImageWindow *win )
 	/* Panning windows should use scroll to zoom, according to the HIG.
 	 */
 	controller = GTK_EVENT_CONTROLLER( gtk_event_controller_scroll_new( 
-		GTK_EVENT_CONTROLLER_SCROLL_DISCRETE |
 		GTK_EVENT_CONTROLLER_SCROLL_VERTICAL ) );
 	g_signal_connect( controller, "scroll", 
 		G_CALLBACK( image_window_scroll ), win );