- Added `tab_selected` signal which has same behavior as `tab_changed`

lest breaking current API, though, it is noted in the documentation of TabContainer
class, of the upcoming Godot (v3.0+) changes in behavior, that is, `tab_selected` will be
emitted for selecting any tab, while `tab_changed` only if a tab changes.
- Added `get_previous_tab()`. Which returns the previous shown tab. **Note:** In Godot v3.0+, only `tab_changed` can modify previous tab index.
- Add documentation for the added function and signals. Fix a typo too.

3 files changed, 68 insertions, 33 deletions

diff --git a/doc/base/classes.xml b/doc/base/classes.xml
index 16de2a337..5fa0e11e8 100644
--- a/doc/base/classes.xml
+++ b/doc/base/classes.xml
@@ -39867,13 +39867,21 @@
 			<return type="int">
 			</return>
 			<description>
-				Return the current tab that is being showed.
+				Return the current tab index that is being shown.
 			</description>
 		</method>
+		<method name="get_previous_tab" qualifiers="const">
+			<return type="int">
+			</return>
+			<description>
+				Return the previous tab index that was being shown.
+ 			</description>
+ 		</method>
 		<method name="get_current_tab_control" qualifiers="const">
 			<return type="Control">
 			</return>
 			<description>
+				Return the current tab control that is being shown.
 			</description>
 		</method>
 		<method name="get_popup" qualifiers="const">
@@ -39976,9 +39984,16 @@
 			<argument index="0" name="tab" type="int">
 			</argument>
 			<description>
-				Emitted when the current tab changes.
+				Emitted when a tab gets selected. Same behavior as [tab_selected] signal for backward compatibility. Note: In Godot v3.0+ this will change to be only emitted when tab gets changed.
 			</description>
 		</signal>
+		<signal name="tab_selected">
+			<argument index="0" name="tab" type="int">
+			</argument>
+			<description>
+				Emitted when a tab is being selected, even if it is the same tab.
+ 			</description>
+ 		</signal>
 	</signals>
 	<constants>
 	</constants>
diff --git a/scene/gui/tab_container.cpp b/scene/gui/tab_container.cpp
index 47246b8fd..e1895fcf8 100644
--- a/scene/gui/tab_container.cpp
+++ b/scene/gui/tab_container.cpp
@@ -414,8 +414,9 @@ void TabContainer::add_child_notify(Node *p_child) {
 	else {
 		c->show();
 		//call_deferred("set_current_tab",0);
-		first=true;
-		current=0;
+		first = true;
+		current = 0;
+		previous = 0;
 	}
 	c->set_area_as_parent_rect();
 	if (tabs_visible)
@@ -451,7 +452,8 @@ void TabContainer::set_current_tab(int p_current) {
 
 	ERR_FAIL_INDEX( p_current, get_tab_count() );
 
-	current=p_current;
+	int pending_previous = current;
+	current = p_current;
 
 	int idx=0;
 
@@ -478,7 +480,13 @@ void TabContainer::set_current_tab(int p_current) {
 	}
 
 	_change_notify("current_tab");
-	emit_signal("tab_changed",current);
+	
+	if (pending_previous != current)
+		previous = pending_previous;
+
+	emit_signal("tab_selected", current);
+	emit_signal("tab_changed", current);
+
 	update();
 }
 
@@ -487,6 +495,11 @@ int TabContainer::get_current_tab() const {
 	return current;
 }
 
+int TabContainer::get_previous_tab() const {
+	
+		return previous;
+}
+
 Control* TabContainer::get_tab_control(int p_idx) const {
 
 	int idx=0;
@@ -508,6 +521,7 @@ Control* TabContainer::get_tab_control(int p_idx) const {
 
 	return NULL;
 }
+
 Control* TabContainer::get_current_tab_control() const {
 
 	int idx=0;
@@ -555,6 +569,7 @@ void TabContainer::set_tab_align(TabAlign p_align) {
 
 	_change_notify("tab_align");
 }
+
 TabContainer::TabAlign TabContainer::get_tab_align() const {
 
 	return align;
@@ -711,26 +726,28 @@ Popup* TabContainer::get_popup() const {
 
 void TabContainer::_bind_methods() {
 
-	ObjectTypeDB::bind_method(_MD("_input_event"),&TabContainer::_input_event);
-	ObjectTypeDB::bind_method(_MD("get_tab_count"),&TabContainer::get_tab_count);
-	ObjectTypeDB::bind_method(_MD("set_current_tab","tab_idx"),&TabContainer::set_current_tab);
-	ObjectTypeDB::bind_method(_MD("get_current_tab"),&TabContainer::get_current_tab);
-	ObjectTypeDB::bind_method(_MD("get_current_tab_control:Control"),&TabContainer::get_current_tab_control);
-	ObjectTypeDB::bind_method(_MD("get_tab_control:Control","idx"),&TabContainer::get_tab_control);
-	ObjectTypeDB::bind_method(_MD("set_tab_align","align"),&TabContainer::set_tab_align);
-	ObjectTypeDB::bind_method(_MD("get_tab_align"),&TabContainer::get_tab_align);
-	ObjectTypeDB::bind_method(_MD("set_tabs_visible","visible"),&TabContainer::set_tabs_visible);
-	ObjectTypeDB::bind_method(_MD("are_tabs_visible"),&TabContainer::are_tabs_visible);
-	ObjectTypeDB::bind_method(_MD("set_tab_title","tab_idx","title"),&TabContainer::set_tab_title);
-	ObjectTypeDB::bind_method(_MD("get_tab_title","tab_idx"),&TabContainer::get_tab_title);
-	ObjectTypeDB::bind_method(_MD("set_tab_icon","tab_idx","icon:Texture"),&TabContainer::set_tab_icon);
-	ObjectTypeDB::bind_method(_MD("get_tab_icon:Texture","tab_idx"),&TabContainer::get_tab_icon);
-	ObjectTypeDB::bind_method(_MD("set_popup","popup:Popup"),&TabContainer::set_popup);
-	ObjectTypeDB::bind_method(_MD("get_popup:Popup"),&TabContainer::get_popup);
+	ObjectTypeDB::bind_method(_MD("_input_event"), &TabContainer::_input_event);
+	ObjectTypeDB::bind_method(_MD("get_tab_count"), &TabContainer::get_tab_count);
+	ObjectTypeDB::bind_method(_MD("set_current_tab","tab_idx"), &TabContainer::set_current_tab);
+	ObjectTypeDB::bind_method(_MD("get_current_tab"), &TabContainer::get_current_tab);
+	ObjectTypeDB::bind_method(_MD("get_previous_tab"), &TabContainer::get_previous_tab);
+	ObjectTypeDB::bind_method(_MD("get_current_tab_control:Control"), &TabContainer::get_current_tab_control);
+	ObjectTypeDB::bind_method(_MD("get_tab_control:Control","idx"), &TabContainer::get_tab_control);
+	ObjectTypeDB::bind_method(_MD("set_tab_align","align"), &TabContainer::set_tab_align);
+	ObjectTypeDB::bind_method(_MD("get_tab_align"), &TabContainer::get_tab_align);
+	ObjectTypeDB::bind_method(_MD("set_tabs_visible","visible"), &TabContainer::set_tabs_visible);
+	ObjectTypeDB::bind_method(_MD("are_tabs_visible"), &TabContainer::are_tabs_visible);
+	ObjectTypeDB::bind_method(_MD("set_tab_title","tab_idx","title"), &TabContainer::set_tab_title);
+	ObjectTypeDB::bind_method(_MD("get_tab_title","tab_idx"), &TabContainer::get_tab_title);
+	ObjectTypeDB::bind_method(_MD("set_tab_icon","tab_idx","icon:Texture"), &TabContainer::set_tab_icon);
+	ObjectTypeDB::bind_method(_MD("get_tab_icon:Texture","tab_idx"), &TabContainer::get_tab_icon);
+	ObjectTypeDB::bind_method(_MD("set_popup","popup:Popup"), &TabContainer::set_popup);
+	ObjectTypeDB::bind_method(_MD("get_popup:Popup"), &TabContainer::get_popup);
 
-	ObjectTypeDB::bind_method(_MD("_child_renamed_callback"),&TabContainer::_child_renamed_callback);
+	ObjectTypeDB::bind_method(_MD("_child_renamed_callback"), &TabContainer::_child_renamed_callback);
 
-	ADD_SIGNAL(MethodInfo("tab_changed",PropertyInfo(Variant::INT,"tab")));
+	ADD_SIGNAL(MethodInfo("tab_changed", PropertyInfo(Variant::INT, "tab")));
+	ADD_SIGNAL(MethodInfo("tab_selected", PropertyInfo(Variant::INT, "tab")));
 	ADD_SIGNAL(MethodInfo("pre_popup_pressed"));
 
 	ADD_PROPERTY( PropertyInfo(Variant::INT, "tab_align", PROPERTY_HINT_ENUM,"Left,Center,Right"), _SCS("set_tab_align"), _SCS("get_tab_align") );
@@ -741,13 +758,14 @@ void TabContainer::_bind_methods() {
 
 TabContainer::TabContainer() {
 
-	tab_display_ofs=0;
-	buttons_visible_cache=false;
-	tabs_ofs_cache=0;
-	current=0;
-	mouse_x_cache=0;
-	align=ALIGN_CENTER;
-	tabs_visible=true;
-	popup=NULL;
+	tab_display_ofs = 0;
+	buttons_visible_cache = false;
+	tabs_ofs_cache = 0;
+	current = 0;
+	previous = 0;
+	mouse_x_cache = 0;
+	align = ALIGN_CENTER;
+	tabs_visible = true;
+	popup = NULL;
 
 }
diff --git a/scene/gui/tab_container.h b/scene/gui/tab_container.h
index d63caf173..2142d4b82 100644
--- a/scene/gui/tab_container.h
+++ b/scene/gui/tab_container.h
@@ -50,6 +50,7 @@ private:
 	int tabs_ofs_cache;
 	int last_tab_cache;
 	int current;
+	int previous;
 	bool tabs_visible;
 	bool buttons_visible_cache;
 	TabAlign align;
@@ -86,7 +87,8 @@ public:
 	int get_tab_count() const;
 	void set_current_tab(int p_current);
 	int get_current_tab() const;
-
+	int get_previous_tab() const;
+	
 	Control* get_tab_control(int p_idx) const;
 	Control* get_current_tab_control() const;