Fix magnifying by mouse wheel causing scrolling inside windows user is zooming in

src/core/events.c

@@ -31,6 +31,7 @@
 #include "core/display-private.h"
 #include "core/keybindings-private.h"
 #include "core/window-private.h"
+#include "core/zoom-grab.h"
 #include "meta/meta-backend.h"
 
 #ifdef HAVE_NATIVE_BACKEND
@@ -291,6 +292,10 @@ meta_display_handle_event (MetaDisplay        *display,
             meta_display_a11y_zoom (display, FALSE);
           }
 
+        /* Hold an active pointer grab so subsequent scroll-valuator motion
+         * events in this gesture are captured and not delivered to clients. */
+        meta_zoom_pointer_grab_ensure (display, clutter_event_get_time (event));
+
         bypass_wayland = bypass_clutter = TRUE;
         goto out;
       }

src/core/keybindings-private.h

@@ -126,6 +126,12 @@ typedef struct
   /* Alt+click button grabs */
   ClutterModifierType window_grab_modifiers;
   ClutterModifierType mouse_zoom_modifiers;
+
+  /* Active pointer grab held during a11y mouse-wheel zoom, so that
+   * scroll-valuator motion events are not delivered to client windows
+   * (passive button-4/5 grabs cannot intercept XI_Motion scroll events). */
+  gboolean zoom_pointer_grab_active;
+  guint    zoom_pointer_grab_timeout_id;
 } MetaKeyBindingManager;
 
 void     meta_display_init_keys             (MetaDisplay *display);

src/core/keybindings.c

@@ -37,6 +37,7 @@
 #include "core/edge-resistance.h"
 #include "core/frame.h"
 #include "core/keybindings-private.h"
+#include "core/zoom-grab.h"
 #include "core/meta-accel-parse.h"
 #include "core/meta-workspace-manager-private.h"
 #include "core/workspace-private.h"
@@ -1500,6 +1501,8 @@ meta_display_shutdown_keys (MetaDisplay *display)
 
   meta_prefs_remove_listener (prefs_changed_callback, display);
 
+  meta_zoom_pointer_grab_release_all (display);
+
   g_hash_table_destroy (keys->key_bindings_index);
   g_hash_table_destroy (keys->key_bindings);
 

src/core/zoom-grab.c

@@ -0,0 +1,83 @@
+/*
+ * Zoom pointer grab.
+ *
+ * Cinnamon's magnifier (Accessibility > Zoom) can be driven by holding a
+ * configurable modifier and turning the mouse wheel. On X11, scroll-valuator
+ * motion events are delivered directly to the client window under the pointer
+ * by the X server, so the magnified application keeps scrolling while the user
+ * is zooming. The passive button-4/5 grab in keybindings.c cannot intercept
+ * XI_Motion scroll events, so we hold a short-lived active pointer grab for
+ * the duration of the zoom gesture; an active grab captures all pointer
+ * events, including scroll-valuator motion. The grab is released shortly after
+ * the last zoom-scroll event so normal pointer interaction resumes promptly.
+ */
+
+#include "config.h"
+#include "core/zoom-grab.h"
+#include "core/keybindings-private.h"
+#include "backends/meta-backend-private.h"
+#include "meta/meta-backend.h"
+
+#define ZOOM_GRAB_IDLE_MS 350
+
+static gboolean
+zoom_pointer_grab_release (gpointer user_data)
+{
+  MetaDisplay *display = META_DISPLAY (user_data);
+  MetaKeyBindingManager *keys = &display->key_binding_manager;
+
+  if (keys->zoom_pointer_grab_active)
+    {
+      meta_backend_ungrab_device (meta_get_backend (),
+                                  META_VIRTUAL_CORE_POINTER_ID,
+                                  CLUTTER_CURRENT_TIME);
+      keys->zoom_pointer_grab_active = FALSE;
+    }
+
+  keys->zoom_pointer_grab_timeout_id = 0;
+  return G_SOURCE_REMOVE;
+}
+
+void
+meta_zoom_pointer_grab_ensure (MetaDisplay *display,
+                               uint32_t     timestamp)
+{
+  MetaKeyBindingManager *keys = &display->key_binding_manager;
+
+  if (meta_is_wayland_compositor ())
+    return;
+
+  if (!keys->zoom_pointer_grab_active)
+    {
+      keys->zoom_pointer_grab_active =
+        meta_backend_grab_device (meta_get_backend (),
+                                  META_VIRTUAL_CORE_POINTER_ID,
+                                  timestamp);
+    }
+
+  if (keys->zoom_pointer_grab_timeout_id)
+    g_source_remove (keys->zoom_pointer_grab_timeout_id);
+  keys->zoom_pointer_grab_timeout_id =
+    g_timeout_add_full (G_PRIORITY_DEFAULT, ZOOM_GRAB_IDLE_MS,
+                        zoom_pointer_grab_release, display, NULL);
+}
+
+void
+meta_zoom_pointer_grab_release_all (MetaDisplay *display)
+{
+  MetaKeyBindingManager *keys = &display->key_binding_manager;
+
+  if (keys->zoom_pointer_grab_timeout_id)
+    {
+      g_source_remove (keys->zoom_pointer_grab_timeout_id);
+      keys->zoom_pointer_grab_timeout_id = 0;
+    }
+
+  if (keys->zoom_pointer_grab_active)
+    {
+      meta_backend_ungrab_device (meta_get_backend (),
+                                  META_VIRTUAL_CORE_POINTER_ID,
+                                  CLUTTER_CURRENT_TIME);
+      keys->zoom_pointer_grab_active = FALSE;
+    }
+}

src/core/zoom-grab.h

@@ -0,0 +1,25 @@
+/*
+ * Zoom pointer grab.
+ *
+ * Cinnamon's magnifier (Accessibility > Zoom) can be driven by holding a
+ * configurable modifier and turning the mouse wheel. On X11, scroll-valuator
+ * motion events are delivered directly to the client window under the pointer
+ * by the X server, so the magnified application keeps scrolling while the user
+ * is zooming. The passive button-4/5 grab in keybindings.c cannot intercept
+ * XI_Motion scroll events, so we hold a short-lived active pointer grab for
+ * the duration of the zoom gesture; an active grab captures all pointer
+ * events, including scroll-valuator motion. The grab is released shortly after
+ * the last zoom-scroll event so normal pointer interaction resumes promptly.
+ */
+
+#ifndef META_ZOOM_GRAB_H
+#define META_ZOOM_GRAB_H
+
+#include "core/display-private.h"
+
+void meta_zoom_pointer_grab_ensure (MetaDisplay *display,
+                                    uint32_t     timestamp);
+
+void meta_zoom_pointer_grab_release_all (MetaDisplay *display);
+
+#endif /* META_ZOOM_GRAB_H */

src/meson.build

@@ -343,6 +343,8 @@ muffin_sources = [
   'core/meta-accel-parse.c',
   'core/meta-accel-parse.h',
   'core/meta-anonymous-file.c',
+  'core/zoom-grab.c',
+  'core/zoom-grab.h',
   'core/meta-anonymous-file.h',
   'core/meta-border.c',
   'core/meta-border.h',