From c4118a4bf19ae2a5fb168867952e7737ac576204 Mon Sep 17 00:00:00 2001
From: Bill Currie <bill@taniwha.org>
Date: Thu, 25 Nov 2021 17:46:16 +0900
Subject: [PATCH] [util] Add listeners to cvars

Listeners are separate to the main callback as listeners have only
read-only access to the objects, but the main callback is free to modify
the cvar and thus can act as a parser and validator. The listeners are
invoked after the main callback if the cvar is modified. There does not
need to be a main callback for the listeners to be invoked.
---
 include/QF/cvar.h |  8 ++++++++
 libs/util/cvar.c  | 37 ++++++++++++++++++++++++++++++++++---
 2 files changed, 42 insertions(+), 3 deletions(-)

diff --git a/include/QF/cvar.h b/include/QF/cvar.h
index 461ff4bf6..2fe20aafa 100644
--- a/include/QF/cvar.h
+++ b/include/QF/cvar.h
@@ -33,6 +33,7 @@
 */
 ///@{
 
+#include "QF/listener.h"
 #include "QF/qtypes.h"
 #include "QF/quakeio.h"
 
@@ -51,6 +52,7 @@ typedef struct cvar_s {
 		\param var	This cvar.
 	*/
 	void      (*callback)(struct cvar_s *var);
+	struct cvar_listener_set_s *listeners;
 	const char *description;	///< for "help" command
 	float       value;			///< The current cvar value as a float
 	int         int_val;		///< The current cvar value as an integer
@@ -58,6 +60,10 @@ typedef struct cvar_s {
 	struct cvar_s *next;		///< \internal Linked list of cvars.
 } cvar_t;
 
+typedef struct cvar_listener_set_s LISTENER_SET_TYPE (cvar_t)
+	cvar_listener_set_t;
+typedef void (*cvar_listener_t) (void *data, const cvar_t *cvar);
+
 typedef struct cvar_alias_s {
 	char       *name;			///< The name of the alias.
 	cvar_t     *cvar;			///< The cvar to which this alias refers
@@ -97,6 +103,8 @@ cvar_t	*Cvar_FindAlias (const char *alias_name);
 
 cvar_t	*Cvar_MakeAlias (const char *name, cvar_t *cvar);
 cvar_t	*Cvar_RemoveAlias (const char *name);
+void Cvar_AddListener (cvar_t *cvar, cvar_listener_t listener, void *data);
+void Cvar_RemoveListener (cvar_t *cvar, cvar_listener_t listener, void *data);
 
 // equivelants to "<name> <variable>" typed at the console
 void 	Cvar_Set (cvar_t *var, const char *value);
diff --git a/libs/util/cvar.c b/libs/util/cvar.c
index 333e1ca9b..add043f11 100644
--- a/libs/util/cvar.c
+++ b/libs/util/cvar.c
@@ -249,6 +249,24 @@ Cvar_CompleteBuildList (const char *partial)
 	return buf;
 }
 
+VISIBLE void
+Cvar_AddListener (cvar_t *cvar, cvar_listener_t listener, void *data)
+{
+	if (!cvar->listeners) {
+		cvar->listeners = malloc (sizeof (*cvar->listeners));
+		LISTENER_SET_INIT (cvar->listeners, 8);
+	}
+	LISTENER_ADD (cvar->listeners, listener, data);
+}
+
+VISIBLE void
+Cvar_RemoveListener (cvar_t *cvar, cvar_listener_t listener, void *data)
+{
+	if (cvar->listeners) {
+		LISTENER_REMOVE (cvar->listeners, listener, data);
+	}
+}
+
 VISIBLE void
 Cvar_Set (cvar_t *var, const char *value)
 {
@@ -279,6 +297,10 @@ Cvar_Set (cvar_t *var, const char *value)
 
 		if (var->callback)
 			var->callback (var);
+
+		if (var->listeners) {
+			LISTENER_INVOKE (var->listeners, var);
+		}
 	}
 }
 
@@ -710,7 +732,7 @@ VISIBLE cvar_t *
 Cvar_Get (const char *name, const char *string, int cvarflags,
 		  void (*callback)(cvar_t*), const char *description)
 {
-
+	int         changed = 0;
 	cvar_t     *var;
 
 	if (Cmd_Exists (name)) {
@@ -740,10 +762,13 @@ Cvar_Get (const char *name, const char *string, int cvarflags,
 				break;
 		var->next = *v;
 		*v = var;
+
+		changed = 1;
 	} else {
 		// Cvar does exist, so we update the flags and return.
 		var->flags &= ~CVAR_USER_CREATED;
 		var->flags |= cvarflags;
+		changed = !strequal (var->string, string) || var->callback != callback;
 		if (!var->callback)
 			var->callback = callback;
 		if (!var->description
@@ -753,8 +778,14 @@ Cvar_Get (const char *name, const char *string, int cvarflags,
 		if (!var->default_string)
 			var->default_string = strdup (string);
 	}
-	if (var->callback)
-		var->callback (var);
+	if (changed) {
+		if (var->callback)
+			var->callback (var);
+
+		if (var->listeners) {
+			LISTENER_INVOKE (var->listeners, var);
+		}
+	}
 
 	return var;
 }