Option to have focus_follows_mouse only on drops

Fixes #9896

docs/changelog.rst

@@ -255,6 +255,8 @@ Detailed list of changes
 
 - diff kitten: Keep the current (topmost) filename visible when scrolling, controlled by a new option :opt:`kitten-diff.sticky_header` (:pull:`9891`)
 
+- Add an option to :opt:`focus_follows_mouse` to only switch focus on drops rather than movement (:pull:`9896`)
+
 
 0.46.2 [2026-03-21]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

kitty/glfw.c

@@ -843,6 +843,9 @@ on_drop(GLFWwindow *window, GLFWDropEvent *ev) {
                 ev->from_self ? Py_True : Py_False, Py_True);
             break;
         case GLFW_DROP_DROP:
+            if (w && OPT(focus_follows_mouse).on_drop) {
+                call_boss(set_active_window, "KO", w->id, Py_True);
+            }
             Py_CLEAR(global_state.drop_dest.data);
             global_state.drop_dest.drop_has_happened = true;
             global_state.drop_dest.client_window_data_request = 0;

kitty/mouse.c

@@ -196,7 +196,7 @@ set_currently_hovered_window(id_type window_id, int modifiers) {
                 debug("Sent mouse leave event to window: %llu\n", left_window->id);
             }
         }
-        if (window_id && OPT(focus_follows_mouse) && global_state.callback_os_window && global_state.callback_os_window->num_tabs) {
+        if (window_id && OPT(focus_follows_mouse).on_cross && global_state.callback_os_window && global_state.callback_os_window->num_tabs) {
             Tab *t = global_state.callback_os_window->tabs + global_state.callback_os_window->active_tab;
             for (unsigned i = 0; i < t->num_windows; i++) {
                 if (t->windows[i].id == window_id) {

kitty/options/definition.py

@@ -855,12 +855,13 @@ fallback to 0.5.
     )
 
 opt('focus_follows_mouse', 'no',
-    option_type='to_bool', ctype='bool',
+    choices=('no', 'n', 'false', 'y', 'yes', 'true', 'drop'), ctype='!focus_follows_mouse',
     long_text='''
 Set the active window to the window under the mouse when the mouse crosses
 into a different window. The active window does not change while the mouse
 moves around within a single window, so an accidental mouse bump will not
-undo a keyboard-driven window switch.
+undo a keyboard-driven window switch. Setting it to :code:`drop` means
+focus will only be changed when a drag and drop happens in a window.
 On macOS, this will also cause the OS Window under the mouse to be focused automatically when the
 mouse enters it, as long as the kitty application is the active application.
 '''

kitty/options/parse.py

@@ -1012,7 +1012,12 @@ class Parser:
             ans["filter_notification"][k] = v
 
     def focus_follows_mouse(self, val: str, ans: dict[str, typing.Any]) -> None:
-        ans['focus_follows_mouse'] = to_bool(val)
+        val = val.lower()
+        if val not in self.choices_for_focus_follows_mouse:
+            raise ValueError(f"The value {val} is not a valid choice for focus_follows_mouse")
+        ans["focus_follows_mouse"] = val
+
+    choices_for_focus_follows_mouse = frozenset(('no', 'n', 'false', 'y', 'yes', 'true', 'drop'))
 
     def font_family(self, val: str, ans: dict[str, typing.Any]) -> None:
         ans['font_family'] = parse_font_spec(val)

kitty/options/to-c-generated.h

@@ -683,7 +683,7 @@ convert_from_opts_click_interval(PyObject *py_opts, Options *opts) {
 
 static void
 convert_from_python_focus_follows_mouse(PyObject *val, Options *opts) {
-    opts->focus_follows_mouse = PyObject_IsTrue(val);
+    focus_follows_mouse(val, opts);
 }
 
 static void

kitty/options/to-c.h

@@ -558,6 +558,22 @@ tab_bar_style(PyObject *val, Options *opts) {
     opts->tab_bar_hidden = PyUnicode_CompareWithASCIIString(val, "hidden") == 0 ? true: false;
 }
 
+static inline void
+focus_follows_mouse(PyObject *val, Options *opts) {
+    zero_at_ptr(&opts->focus_follows_mouse);
+    const char *q = PyUnicode_AsUTF8(val);
+    switch(q[0]) {
+        case 'y': case 't':
+            opts->focus_follows_mouse.on_cross = true;
+            opts->focus_follows_mouse.on_drop = true;
+            break;
+        case 'd':
+            opts->focus_follows_mouse.on_drop = true;
+            break;
+    }
+}
+
+
 static inline void
 tab_bar_margin_height(PyObject *val, Options *opts) {
     if (!PyTuple_Check(val) || PyTuple_GET_SIZE(val) != 2) {

kitty/options/types.py

@@ -22,6 +22,7 @@ choices_for_allow_cloning = typing.Literal['yes', 'y', 'true', 'no', 'n', 'false
 choices_for_allow_remote_control = typing.Literal['password', 'socket-only', 'socket', 'no', 'n', 'false', 'yes', 'y', 'true']
 choices_for_background_image_layout = typing.Literal['mirror-tiled', 'scaled', 'tiled', 'clamped', 'centered', 'cscaled']
 choices_for_default_pointer_shape = typing.Literal['arrow', 'beam', 'text', 'pointer', 'hand', 'help', 'wait', 'progress', 'crosshair', 'cell', 'vertical-text', 'move', 'e-resize', 'ne-resize', 'nw-resize', 'n-resize', 'se-resize', 'sw-resize', 's-resize', 'w-resize', 'ew-resize', 'ns-resize', 'nesw-resize', 'nwse-resize', 'zoom-in', 'zoom-out', 'alias', 'copy', 'not-allowed', 'no-drop', 'grab', 'grabbing']
+choices_for_focus_follows_mouse = typing.Literal['no', 'n', 'false', 'y', 'yes', 'true', 'drop']
 choices_for_linux_display_server = typing.Literal['auto', 'wayland', 'x11']
 choices_for_macos_colorspace = typing.Literal['srgb', 'default', 'displayp3']
 choices_for_macos_show_window_title_in = typing.Literal['all', 'menubar', 'none', 'window']
@@ -578,7 +579,7 @@ class Options:
     enable_audio_bell: bool = True
     enabled_layouts: list[str] = ['fat', 'grid', 'horizontal', 'splits', 'stack', 'tall', 'vertical']
     file_transfer_confirmation_bypass: str = ''
-    focus_follows_mouse: bool = False
+    focus_follows_mouse: choices_for_focus_follows_mouse = 'no'
     font_family: FontSpec = FontSpec(family=None, style=None, postscript_name=None, full_name=None, system='monospace', axes=(), variable_name=None, features=(), created_from_string='monospace')
     font_size: float = 11.0
     force_ltr: bool = False

kitty/state.h

@@ -74,7 +74,9 @@ typedef struct Options {
     color_type url_color, background, foreground, active_border_color, inactive_border_color, bell_border_color, tab_bar_background, tab_bar_margin_color,
         window_title_bar_active_foreground, window_title_bar_active_background, window_title_bar_inactive_foreground, window_title_bar_inactive_background;
     monotonic_t repaint_delay, input_delay;
-    bool focus_follows_mouse;
+    struct {
+        bool on_cross, on_drop;
+    } focus_follows_mouse;
     unsigned int hide_window_decorations;
     bool macos_hide_from_tasks, macos_quit_when_last_window_closed, macos_window_resizable, macos_traditional_fullscreen, macos_fullscreen_ignore_safe_area_insets;
     unsigned int macos_option_as_alt;