a few refinements to the new comm node selection feature

1. Don't display the selection arrows until the selection is actually moved, to avoid interfering with the standard selection feature
2. Use static variables and the new `TIMESTAMP` data type
3. Minor cleanup

Follow-up to #6736.

Author: Goober5000

code/hud/hudsquadmsg.cpp

@@ -44,7 +44,7 @@ static int Msg_key_used;								// local variable which tells if the key being p
 															// with the messaging system was actually used
 static int Msg_key;                         // global which indicates which key was currently pressed
 static bool Msg_key_set_from_scripting; // is true if the key was set from scripting and not from a player keypress
-static int Msg_mode_timestamp;
+static TIMESTAMP Msg_mode_timestamp;
 int Msg_instance;						// variable which holds ship/wing instance to send the message to
 int Msg_shortcut_command;			// holds command when using a shortcut key
 static int Msg_target_objnum;           // id of the current target of the player
@@ -107,9 +107,10 @@ char Squad_msg_title[256] = "";
 mmode_item MsgItems[MAX_MENU_ITEMS];
 int Num_menu_items = -1; // number of items for a message menu
 
-int First_menu_item = -1;							// index of first item in the menu. This tracks what element of comms options collection is displayed as first option, and displays the next 9 options. Changes only by +/- MAX_MENU_ITEMS (10)
-int Selected_menu_item = First_menu_item;           //!< index of selected item in the menu. Possible index range: 0 - 9, assuming MAX_MENU_ITEMS == 10, and First_menu_item gets initialized
-SCP_string Lua_sqd_msg_cat;
+static int First_menu_item = -1;							// index of first item in the menu. This tracks what element of comms options collection is displayed as first option, and displays the next 9 options. Changes only by +/- MAX_MENU_ITEMS (10)
+static int Selected_menu_item = First_menu_item;           //!< index of selected item in the menu. Possible index range: 0 - 9, assuming MAX_MENU_ITEMS == 10, and First_menu_item gets initialized
+static bool Display_selector = false;
+static SCP_string Lua_sqd_msg_cat;
 
 #define MAX_KEYS_NO_SCROLL	10
 #define MAX_KEYS_USED		12		// maximum number of keys used for the messaging system
@@ -220,8 +221,10 @@ void hud_squadmsg_start()
 	Num_menu_items = -1;													// reset the menu items
 	First_menu_item = 0;
 	Selected_menu_item = First_menu_item;                            // make first menu item a selected object
+	Display_selector = false;
+
 	Squad_msg_mode = SM_MODE_TYPE_SELECT;							// start off at the base state
-	Msg_mode_timestamp = timestamp(DEFAULT_MSG_TIMEOUT);		// initialize our timer to bogus value
+	Msg_mode_timestamp = _timestamp(DEFAULT_MSG_TIMEOUT);		// initialize our timer to bogus value
 	Msg_shortcut_command = -1;											// assume no shortcut key being used
 	Msg_target_objnum = Player_ai->target_objnum;				// save the players target object number
 	Msg_targeted_subsys = Player_ai->targeted_subsys;				// save the players currently targted subsystem
@@ -496,10 +499,11 @@ void hud_squadmsg_selection_move_down() {
 	{
 		//move down
 		++Selected_menu_item;
+		Display_selector = true;
 
-		//play scrolling sound and reset the comms window timeout timer, so the window doesn't dissapear while we select our item
+		//play scrolling sound and reset the comms window timeout timer, so the window doesn't disappear while we select our item
 		gamesnd_play_iface(InterfaceSounds::SCROLL);
-		Msg_mode_timestamp = timestamp(DEFAULT_MSG_TIMEOUT);
+		Msg_mode_timestamp = _timestamp(DEFAULT_MSG_TIMEOUT);
 
 		//Move to next page if we went outside of current one
 		if (Selected_menu_item == MAX_MENU_DISPLAY 
@@ -525,10 +529,11 @@ void hud_squadmsg_selection_move_up() {
 	{
 		//move up
 		--Selected_menu_item;
+		Display_selector = true;
 
-		//play scrolling sound and reset the comms window timeout timer, so the window doesn't dissapear while we select our item
+		//play scrolling sound and reset the comms window timeout timer, so the window doesn't disappear while we select our item
 		gamesnd_play_iface(InterfaceSounds::SCROLL);
-		Msg_mode_timestamp = timestamp(DEFAULT_MSG_TIMEOUT);
+		Msg_mode_timestamp = _timestamp(DEFAULT_MSG_TIMEOUT);
 
 		//Move to previous page if it exists
 		if (Selected_menu_item < 0 && First_menu_item > 0)
@@ -550,7 +555,7 @@ void hud_squadmsg_selection_move_up() {
 }
 
 //function that tricks hud_squadmsg_get_key() into thinking player selected a menu item with a num key press
-//Yes, this is a pretty much a hack, but it's simple and works with every squadmsq type.
+//Yes, this is a pretty much a hack, but it's simple and works with every squadmsg type.
 void hud_squadmsg_selection_select() {
 
 	//Check if comms menu is up
@@ -2604,7 +2609,7 @@ int hud_squadmsg_do_frame( )
 	HUD_reset_clip();		// JAS: Is this needed?
 
 	if ( Msg_key_used || target_changed ) {
-		Msg_mode_timestamp = timestamp(DEFAULT_MSG_TIMEOUT);
+		Msg_mode_timestamp = _timestamp(DEFAULT_MSG_TIMEOUT);
 		return 1;
 	} else
 		return 0;
@@ -2925,7 +2930,7 @@ void HudGaugeSquadMessage::render(float  /*frametime*/, bool config)
 
 	for (int i = 0; i < nitems; i++ ) {
 		int item_num;
-		bool isSelectedItem = First_menu_item + i == First_menu_item + Selected_menu_item;
+		bool isSelectedItem = (i == Selected_menu_item);
 		char text[255];
 
 		if (!config) {
@@ -2967,7 +2972,7 @@ void HudGaugeSquadMessage::render(float  /*frametime*/, bool config)
 		if (MsgItems[First_menu_item + i].active >= 0) {
 			// first print an icon to indicate selected item
 			item_num = (i + 1) % MAX_MENU_DISPLAY;
-			if (isSelectedItem) {
+			if (isSelectedItem && Display_selector) {
 				renderPrintfWithGauge(sx, sy, EG_SQ1 + i, scale, config, XSTR(">>", 1887), item_num); //allow modders to change string and add number
 			}
 			// or do the number