Codechange: Add GetParentWidget() to widgets.

This allows to get parent widgets in the nested tree from bottom-up.

src/widget.cpp

@@ -1319,6 +1319,8 @@ void NWidgetContainer::AdjustPaddingForZoom()
  */
 void NWidgetContainer::Add(NWidgetBase *wid)
 {
+	assert(wid != nullptr);
+	wid->parent = this;
 	assert(wid->next == nullptr && wid->prev == nullptr);
 
 	if (this->head == nullptr) {
@@ -2170,6 +2172,7 @@ NWidgetBackground::NWidgetBackground(WidgetType tp, Colours colour, WidgetID ind
 {
 	assert(tp == WWT_PANEL || tp == WWT_INSET || tp == WWT_FRAME);
 	this->child = child;
+	if (this->child != nullptr) this->child->parent = this;
 	this->SetAlignment(SA_TOP | SA_LEFT);
 }
 
@@ -2190,6 +2193,7 @@ void NWidgetBackground::Add(NWidgetBase *nwid)
 	if (this->child == nullptr) {
 		this->child = new NWidgetVertical();
 	}
+	nwid->parent = this->child;
 	this->child->Add(nwid);
 }
 
@@ -2208,6 +2212,7 @@ void NWidgetBackground::SetPIP(uint8_t pip_pre, uint8_t pip_inter, uint8_t pip_p
 	if (this->child == nullptr) {
 		this->child = new NWidgetVertical();
 	}
+	this->child->parent = this;
 	this->child->SetPIP(pip_pre, pip_inter, pip_post);
 }
 
@@ -2226,6 +2231,7 @@ void NWidgetBackground::SetPIPRatio(uint8_t pip_ratio_pre, uint8_t pip_ratio_int
 	if (this->child == nullptr) {
 		this->child = new NWidgetVertical();
 	}
+	this->child->parent = this;
 	this->child->SetPIPRatio(pip_ratio_pre, pip_ratio_inter, pip_ratio_post);
 }
 

src/widget_type.h

@@ -144,6 +144,34 @@ public:
 	virtual NWidgetCore *GetWidgetFromPos(int x, int y) = 0;
 	virtual NWidgetBase *GetWidgetOfType(WidgetType tp);
 
+	/**
+	 * Get parent widget of type NWID.
+	 * @tparam NWID Type of the nested widget.
+	 * @returns Parent widget, or nullptr if no widget of the specified type is found.
+	 */
+	template <class NWID>
+	NWID *GetParentWidget()
+	{
+		for (NWidgetBase *nwid_parent = this->parent; nwid_parent != nullptr; nwid_parent = nwid_parent->parent) {
+			if (NWID *nwid = dynamic_cast<NWID *>(nwid_parent); nwid != nullptr) return nwid;
+		}
+		return nullptr;
+	}
+
+	/**
+	 * Get parent widget of type NWID.
+	 * @tparam NWID Type of the nested widget.
+	 * @returns Parent widget, or nullptr if no widget of the specified type is found.
+	 */
+	template <class NWID>
+	const NWID *GetParentWidget() const
+	{
+		for (const NWidgetBase *nwid_parent = this->parent; nwid_parent != nullptr; nwid_parent = nwid_parent->parent) {
+			if (const NWID *nwid = dynamic_cast<const NWID *>(nwid_parent); nwid != nullptr) return nwid;
+		}
+		return nullptr;
+	}
+
 	virtual bool IsHighlighted() const { return false; }
 	virtual TextColour GetHighlightColour() const { return TC_INVALID; }
 	virtual void SetHighlighted([[maybe_unused]] TextColour highlight_colour) {}
@@ -213,6 +241,8 @@ public:
 	RectPadding padding;    ///< Padding added to the widget. Managed by parent container widget. (parent container may swap left and right for RTL)
 	RectPadding uz_padding; ///< Unscaled padding, for resize calculation.
 
+	NWidgetBase *parent; ///< Parent widget of this widget, automatically filled in when added to container.
+
 protected:
 	inline void StoreSizePosition(SizingType sizing, int x, int y, uint given_width, uint given_height);
 };