Only grab scrollwheel buttons if necessary.

With this patch, we only grab the scrollwheel buttons (4 and 5) when
managing a window if a whole window key binding exists for these buttons.

This allows both of these usecases:
  - Bindings to scrollwheel buttons using --whole-window (see #1701).
  - Scrolling in a window without focusing it if no such binding
    exists (see #2049).

Furthermore, we drop all button grabs and regrab them after a config
reload in order to reevaluate the new bindings correctly.

fixes #2049

include/bindings.h

@@ -33,6 +33,13 @@ Binding *configure_binding(const char *bindtype, const char *modifiers, const ch
  */
 void grab_all_keys(xcb_connection_t *conn);
 
+/**
+ * Release the button grabs on all managed windows and regrab them,
+ * reevaluating which buttons need to be grabbed.
+ *
+ */
+void regrab_all_buttons(xcb_connection_t *conn);
+
 /**
  * Returns a pointer to the Binding that matches the given xcb event or NULL if
  * no such binding exists.
@@ -95,3 +102,12 @@ CommandResult *run_binding(Binding *bind, Con *con);
  *
  */
 bool load_keymap(void);
+
+/**
+ * Returns true if the current config has any binding to a scroll wheel button
+ * (4 or 5) which is a whole-window binding.
+ * We need this to figure out whether we should grab all buttons or just 1-3
+ * when managing a window. See #2049.
+ *
+ */
+bool bindings_should_grab_scrollwheel_buttons(void);

include/xcb.h

@@ -165,4 +165,4 @@ void xcb_remove_property_atom(xcb_connection_t *conn, xcb_window_t window, xcb_a
  * 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);
+void xcb_grab_buttons(xcb_connection_t *conn, xcb_window_t window, bool bind_scrollwheel);

src/bindings.c

@@ -146,6 +146,27 @@ void grab_all_keys(xcb_connection_t *conn) {
     }
 }
 
+/*
+ * Release the button grabs on all managed windows and regrab them,
+ * reevaluating which buttons need to be grabbed.
+ *
+ */
+void regrab_all_buttons(xcb_connection_t *conn) {
+    bool grab_scrollwheel = bindings_should_grab_scrollwheel_buttons();
+    xcb_grab_server(conn);
+
+    Con *con;
+    TAILQ_FOREACH(con, &all_cons, all_cons) {
+        if (con->window == NULL)
+            continue;
+
+        xcb_ungrab_button(conn, XCB_BUTTON_INDEX_ANY, con->window->id, XCB_BUTTON_MASK_ANY);
+        xcb_grab_buttons(conn, con->window->id, grab_scrollwheel);
+    }
+
+    xcb_ungrab_server(conn);
+}
+
 /*
  * Returns a pointer to the Binding with the specified modifiers and
  * keycode or NULL if no such binding exists.
@@ -778,3 +799,33 @@ bool load_keymap(void) {
 
     return true;
 }
+
+/*
+ * Returns true if the current config has any binding to a scroll wheel button
+ * (4 or 5) which is a whole-window binding.
+ * We need this to figure out whether we should grab all buttons or just 1-3
+ * when managing a window. See #2049.
+ *
+ */
+bool bindings_should_grab_scrollwheel_buttons(void) {
+    Binding *bind;
+    TAILQ_FOREACH(bind, bindings, bindings) {
+        /* We are only interested in whole window mouse bindings. */
+        if (bind->input_type != B_MOUSE || !bind->whole_window)
+            continue;
+
+        char *endptr;
+        long button = strtol(bind->symbol + (sizeof("button") - 1), &endptr, 10);
+        if (button == LONG_MAX || button == LONG_MIN || button < 0 || *endptr != '\0' || endptr == bind->symbol) {
+            ELOG("Could not parse button number, skipping this binding. Please report this bug in i3.\n");
+            continue;
+        }
+
+        /* If the binding is for either scrollwheel button, we need to grab everything. */
+        if (button == 4 || button == 5) {
+            return true;
+        }
+    }
+
+    return false;
+}

src/config.c

@@ -229,6 +229,7 @@ void load_configuration(xcb_connection_t *conn, const char *override_configpath,
     if (reload) {
         translate_keysyms();
         grab_all_keys(conn);
+        regrab_all_buttons(conn);
     }
 
     if (config.font.type == FONT_TYPE_NONE) {

src/manage.c

@@ -168,7 +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);
 
-    xcb_grab_buttons(conn, window, (uint8_t[]) {XCB_BUTTON_INDEX_ANY});
+    xcb_grab_buttons(conn, window, bindings_should_grab_scrollwheel_buttons());
 
     /* 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

@@ -324,8 +324,19 @@ release_grab:
  * 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++) {
+void xcb_grab_buttons(xcb_connection_t *conn, xcb_window_t window, bool bind_scrollwheel) {
+    uint8_t buttons[3];
+    int num = 0;
+
+    if (bind_scrollwheel) {
+        buttons[num++] = XCB_BUTTON_INDEX_ANY;
+    } else {
+        buttons[num++] = XCB_BUTTON_INDEX_1;
+        buttons[num++] = XCB_BUTTON_INDEX_2;
+        buttons[num++] = XCB_BUTTON_INDEX_3;
+    }
+
+    for (int i = 0; i < num; 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);
     }