Add and bind an action to center the cursor

"z" stands for VIM's "zz".

nncmpp.actions

@@ -42,6 +42,7 @@ INCREMENTAL_SEARCH, Incremental search
 
 SCROLL_UP,          Scroll up
 SCROLL_DOWN,        Scroll down
+CENTER_CURSOR,      Center the cursor
 MOVE_UP,            Move selection up
 MOVE_DOWN,          Move selection down
 

nncmpp.c

@@ -2212,6 +2212,19 @@ app_ensure_selection_visible (void)
 		app_scroll (too_low);
 }
 
+static bool
+app_center_cursor (void)
+{
+	struct tab *tab = g.active_tab;
+	if (tab->item_selected < 0 || !tab->item_count)
+		return false;
+
+	int offset = tab->item_selected - tab->item_top;
+	int target = app_visible_items () / 2;
+	app_scroll (offset - target);
+	return true;
+}
+
 static bool
 app_move_selection (int diff)
 {
@@ -2356,7 +2369,7 @@ incremental_search_match (const ucs4_t *needle, size_t len,
 	{
 		size_t i = 0;
 		for (; i < len && start + i < row->chars_len; i++)
-			if (uc_tolower(needle[i]) != uc_tolower(row->chars[start + i].c))
+			if (uc_tolower (needle[i]) != uc_tolower (row->chars[start + i].c))
 				break;
 		best = MAX (best, i);
 	}
@@ -2509,9 +2522,10 @@ app_process_action (enum action action)
 	case ACTION_PULSE_MUTE:             return pulse_volume_mute (&g.pulse);
 #endif  // WITH_PULSE
 
-		// XXX: these should rather be parametrized
+		// XXX: these two should rather be parametrized
 	case ACTION_SCROLL_UP:              return app_scroll (-3);
-	case ACTION_SCROLL_DOWN:            return app_scroll  (3);
+	case ACTION_SCROLL_DOWN:            return app_scroll (+3);
+	case ACTION_CENTER_CURSOR:          return app_center_cursor ();
 
 	case ACTION_GOTO_TOP:
 		if (tab->item_count)
@@ -2737,6 +2751,7 @@ g_normal_defaults[] =
 	{ "C-f",        ACTION_GOTO_PAGE_NEXT     },
 	{ "C-y",        ACTION_SCROLL_UP          },
 	{ "C-e",        ACTION_SCROLL_DOWN        },
+	{ "z",          ACTION_CENTER_CURSOR      },
 
 	{ "H",          ACTION_GOTO_VIEW_TOP      },
 	{ "M",          ACTION_GOTO_VIEW_CENTER   },