Implement an option to have focus follow the mouse

Fixes #156

kitty/config.py

@@ -240,6 +240,7 @@ type_map = {
     'scrollback_in_new_tab': to_bool,
     'font_size': to_font_size,
     'font_size_delta': positive_float,
+    'focus_follows_mouse': to_bool,
     'cursor_shape': to_cursor_shape,
     'open_url_modifiers': to_open_url_modifiers,
     'repaint_delay': positive_int,

kitty/kitty.conf

@@ -90,6 +90,9 @@ select_by_word_characters :@-./_~?&=%+#
 # zero to disable mouse cursor hiding.
 mouse_hide_wait 3.0
 
+# Set the active window to the window under the mouse when moving the mouse around
+focus_follows_mouse no
+
 # The enabled window layouts. A comma separated list of layout names. The special value * means
 # all layouts. The first listed layout will be used as the startup layout.
 # For a list of available layouts, see the file layouts.py

kitty/mouse.c

@@ -164,6 +164,12 @@ detect_url(Window *w, Screen *screen, unsigned int x, unsigned int y) {
 
 HANDLER(handle_move_event) {
     unsigned int x, y;
+    if (OPT(focus_follows_mouse)) {
+        Tab *t = global_state.tabs + global_state.active_tab;
+        if (window_idx != t->active_window) {
+            call_boss(switch_focus_to, "I", window_idx);
+        }
+    }
     if (!cell_for_pos(w, &x, &y)) return;
     Screen *screen = w->render_data.screen;
     detect_url(w, screen, x, y);

kitty/state.c

@@ -151,6 +151,7 @@ PYWRAP1(set_options) {
 #define S(name, convert) { GA(name); global_state.opts.name = convert(ret); Py_DECREF(ret); if (PyErr_Occurred()) return NULL; }
     S(visual_bell_duration, PyFloat_AsDouble);
     S(enable_audio_bell, PyObject_IsTrue);
+    S(focus_follows_mouse, PyObject_IsTrue);
     S(cursor_blink_interval, PyFloat_AsDouble);
     S(cursor_stop_blinking_after, PyFloat_AsDouble);
     S(cursor_shape, PyLong_AsLong);

kitty/state.h

@@ -18,6 +18,7 @@ typedef struct {
     char_type select_by_word_characters[256]; size_t select_by_word_characters_count;
     color_type url_color;
     double repaint_delay, input_delay;
+    bool focus_follows_mouse;
 } Options;
 
 typedef struct {

kitty/window.py

@@ -80,7 +80,6 @@ class Window:
         self.tab_id = tab.id
         self.tabref = weakref.ref(tab)
         self.override_title = None
-        self.last_mouse_cursor_pos = 0, 0
         self.destroyed = False
         self.click_queue = deque(maxlen=3)
         self.geometry = WindowGeometry(0, 0, 0, 0, 0, 0)