Extract function to grab buttons when managing a window.

We refactor the button grabbing into a function to allow the next patch
both to
  - conditionally grab different sets of buttons
  - grab the buttons again when reloading the config.

relates to #2049

include/xcb.h

@@ -160,3 +160,9 @@ void xcb_add_property_atom(xcb_connection_t *conn, xcb_window_t window, xcb_atom
  *
  */
 void xcb_remove_property_atom(xcb_connection_t *conn, xcb_window_t window, xcb_atom_t property, xcb_atom_t atom);
+
+/**
+ * Grab the specified buttons on a window when managing it.
+ *
+ */
+void xcb_grab_buttons(xcb_connection_t *conn, xcb_window_t window, uint8_t* buttons);

src/manage.c

@@ -168,12 +168,7 @@ void manage_window(xcb_window_t window, xcb_get_window_attributes_cookie_t cooki
     cwindow->id = window;
     cwindow->depth = get_visual_depth(attr->visual);
 
-    /* We need to grab buttons 1-3 for click-to-focus and buttons 1-5
-     * to allow for mouse bindings using --whole-window to work correctly. */
-    xcb_grab_button(conn, false, window, XCB_EVENT_MASK_BUTTON_PRESS,
-                    XCB_GRAB_MODE_SYNC, XCB_GRAB_MODE_ASYNC, root, XCB_NONE,
-                    XCB_BUTTON_INDEX_ANY,
-                    XCB_BUTTON_MASK_ANY /* don’t filter for any modifiers */);
+    xcb_grab_buttons(conn, window, (uint8_t[]) {XCB_BUTTON_INDEX_ANY});
 
     /* update as much information as possible so far (some replies may be NULL) */
     window_update_class(cwindow, xcb_get_property_reply(conn, class_cookie, NULL), true);

src/xcb.c

@@ -319,3 +319,14 @@ release_grab:
     FREE(reply);
     xcb_ungrab_server(conn);
 }
+
+/*
+ * Grab the specified buttons on a window when managing it.
+ *
+ */
+void xcb_grab_buttons(xcb_connection_t *conn, xcb_window_t window, uint8_t* buttons) {
+    for (int i = 0; i < sizeof(buttons) / sizeof(uint8_t); i++) {
+        xcb_grab_button(conn, false, window, XCB_EVENT_MASK_BUTTON_PRESS, XCB_GRAB_MODE_SYNC,
+                        XCB_GRAB_MODE_ASYNC, root, XCB_NONE, buttons[i], XCB_BUTTON_MASK_ANY);
+    }
+}