Make cStack page forward/backward a member function

src/dialogxml/widgets/stack.cpp

@@ -13,6 +13,7 @@
 #include "message.hpp"
 #include "pict.hpp"
 #include "scrollbar.hpp"
+#include "mathutil.hpp"
 #include <climits>
 
 bool cStack::hasChild(std::string id) const {
@@ -84,6 +85,17 @@ bool cStack::setPage(size_t n) {
 	return !failed;
 }
 
+void cStack::doSelectPage(int dir, bool loop) {
+	curPage += dir;
+	if(loop){
+		if(curPage < 0) curPage += nPages;
+		else if(curPage >= nPages) curPage -= nPages;
+	}else{
+		curPage = minmax(0, nPages - 1, curPage);
+	}
+	setPage(curPage);
+}
+
 size_t cStack::getPage() const {
 	return curPage;
 }

src/dialogxml/widgets/stack.hpp

@@ -57,6 +57,10 @@ public:
 	/// @param The new page number
 	/// @return false if the page could not be changed, usually due to a focus handler
 	bool setPage(size_t n);
+	/// Page forward or backward in the stack
+	/// @param dir Usually -1 or 1
+	/// @param loop Beyond the first and last page, loop to the other side
+	void doSelectPage(int dir, bool loop = true);
 	/// Get the current page the stack is displaying.
 	/// @return The current page number
 	size_t getPage() const;

src/game/boe.dlgutil.cpp

@@ -1645,11 +1645,7 @@ class cChooseScenario {
 	
 	bool doSelectPage(int dir) {
 		auto& stk = dynamic_cast<cStack&>(me["list"]);
-		int curPage = stk.getPage(), nPages = stk.getPageCount();
+		stk.doSelectPage(dir, true);
-		curPage += dir;
-		if(curPage < 0) curPage += nPages;
-		else if(curPage >= nPages) curPage -= nPages;
-		stk.setPage(curPage);
 		return true;
 	}