UI: Add Frontend API function to get value of T-bar

Also add a Frontend API event for when the T-bar's value changes.

UI/api-interface.cpp

@@ -166,6 +166,11 @@ struct OBSStudioAPI : obs_frontend_callbacks {
 					  Q_ARG(int, position));
 	}
 
+	int obs_frontend_get_tbar_position(void) override
+	{
+		return main->tBar->value();
+	}
+
 	void obs_frontend_get_scene_collections(
 		std::vector<std::string> &strings) override
 	{

UI/obs-frontend-api/obs-frontend-api.cpp

@@ -154,6 +154,11 @@ void obs_frontend_set_tbar_position(int position)
 		c->obs_frontend_set_tbar_position(position);
 }
 
+int obs_frontend_get_tbar_position(void)
+{
+	return !!callbacks_valid() ? c->obs_frontend_get_tbar_position() : 0;
+}
+
 char **obs_frontend_get_scene_collections(void)
 {
 	if (!callbacks_valid())

UI/obs-frontend-api/obs-frontend-api.h

@@ -53,6 +53,8 @@ enum obs_frontend_event {
 
 	OBS_FRONTEND_EVENT_VIRTUALCAM_STARTED,
 	OBS_FRONTEND_EVENT_VIRTUALCAM_STOPPED,
+
+	OBS_FRONTEND_EVENT_TBAR_VALUE_CHANGED,
 };
 
 /* ------------------------------------------------------------------------- */
@@ -106,6 +108,7 @@ EXPORT int obs_frontend_get_transition_duration(void);
 EXPORT void obs_frontend_set_transition_duration(int duration);
 EXPORT void obs_frontend_release_tbar(void);
 EXPORT void obs_frontend_set_tbar_position(int position);
+EXPORT int obs_frontend_get_tbar_position(void);
 
 EXPORT char **obs_frontend_get_scene_collections(void);
 EXPORT char *obs_frontend_get_current_scene_collection(void);

UI/obs-frontend-api/obs-frontend-internal.hpp

@@ -25,6 +25,7 @@ struct obs_frontend_callbacks {
 	virtual void obs_frontend_set_transition_duration(int duration) = 0;
 	virtual void obs_frontend_release_tbar(void) = 0;
 	virtual void obs_frontend_set_tbar_position(int position) = 0;
+	virtual int obs_frontend_get_tbar_position(void) = 0;
 
 	virtual void obs_frontend_get_scene_collections(
 		std::vector<std::string> &strings) = 0;

UI/window-basic-main-transitions.cpp

@@ -840,6 +840,8 @@ void OBSBasic::CreateProgramOptions()
 	tBar->setProperty("themeID", "tBarSlider");
 
 	connect(tBar, SIGNAL(sliderMoved(int)), this, SLOT(TBarChanged(int)));
+	connect(tBar, SIGNAL(valueChanged(int)), this,
+		SLOT(on_tbar_position_valueChanged(int)));
 	connect(tBar, SIGNAL(sliderReleased()), this, SLOT(TBarReleased()));
 
 	layout->addStretch(0);
@@ -993,6 +995,19 @@ void OBSBasic::TBarChanged(int value)
 				       (float)value / T_BAR_PRECISION_F);
 }
 
+int OBSBasic::GetTbarPosition()
+{
+	return tBar->value();
+}
+
+void OBSBasic::on_tbar_position_valueChanged(int value)
+{
+	if (api) {
+		api->on_event(OBS_FRONTEND_EVENT_TBAR_VALUE_CHANGED);
+	}
+
+	UNUSED_PARAMETER(value);
+}
 void OBSBasic::on_modeSwitch_clicked()
 {
 	SetPreviewProgramMode(!IsPreviewProgramMode());

UI/window-basic-main.hpp

@@ -755,6 +755,7 @@ public:
 	void SetService(obs_service_t *service);
 
 	int GetTransitionDuration();
+	int GetTbarPosition();
 
 	inline bool IsPreviewProgramMode() const
 	{
@@ -955,6 +956,7 @@ private slots:
 	void RemoveTransitionClicked();
 	void on_transitionProps_clicked();
 	void on_transitionDuration_valueChanged(int value);
+	void on_tbar_position_valueChanged(int value);
 
 	void on_modeSwitch_clicked();