Keep scroll position when reinstantiating science_report

The `science_report` loses the scroll position when the view is
closed. This is because the object is destroyed and therefore loses
its state.

This commit adds code to track the scroll position in static fields
and restore the state when the `science_report is` reinstantiated.

Closes longturn#2329.

client/views/view_research.cpp

@@ -22,6 +22,8 @@
 #include <QScrollArea>
 #include <QTimer>
 #include <QToolTip>
+#include <qabstractslider.h>
+#include <qscrollbar.h>
 
 // common
 #include "game.h"
@@ -301,6 +303,9 @@ science_report::science_report() : QWidget()
   scroll->setPalette(QPalette(QColor(215, 215, 215)));
   scroll->setWidget(res_diag);
   scroll->setSizePolicy(size_expanding_policy);
+  scroll->horizontalScrollBar()->setValue(
+      science_report::horizontalScrollValue);
+  scroll->verticalScrollBar()->setValue(science_report::verticalScrollValue);
   sci_layout->addWidget(scroll, 4, 0, 1, 10);
 
   QObject::connect(researching_combo,
@@ -314,6 +319,16 @@ science_report::science_report() : QWidget()
                    QOverload<int>::of(&QComboBox::currentIndexChanged), this,
                    &science_report::goal_tech_changed);
 
+  QScrollBar *horizontalScrollBar = scroll->horizontalScrollBar();
+  QObject::connect(horizontalScrollBar,
+                   QOverload<int>::of(&QAbstractSlider::valueChanged), this,
+                   &science_report::setHorizontalScrollValue);
+
+  QScrollBar *verticalScrollBar = scroll->verticalScrollBar();
+  QObject::connect(verticalScrollBar,
+                   QOverload<int>::of(&QAbstractSlider::valueChanged), this,
+                   &science_report::setVerticalScrollValue);
+
   setLayout(sci_layout);
 }
 
@@ -570,6 +585,24 @@ void science_report::push_research()
   }
 }
 
+/**
+   Set the backing field for the horizontal scroll value. This is used
+   to restore the scroll state when the view is reinstantiated.
+*/
+void science_report::setHorizontalScrollValue(int value)
+{
+  science_report::horizontalScrollValue = value;
+}
+
+/**
+   Set the backing field for the vertical scroll value. This is used
+   to restore the scroll state when the view is reinstantiated.
+*/
+void science_report::setVerticalScrollValue(int value)
+{
+  science_report::verticalScrollValue = value;
+}
+
 /**
    Update the science report.
  */

client/views/view_research.h

@@ -71,6 +71,8 @@ struct qlist_item {
 class science_report : public QWidget {
   Q_OBJECT
 
+  static inline int horizontalScrollValue;
+  static inline int verticalScrollValue;
   QComboBox *goal_combo;
   QComboBox *researching_combo;
   QPushButton *refresh_but;
@@ -97,6 +99,8 @@ private slots:
   void current_tech_changed(int index);
   void goal_tech_changed(int index);
   void push_research();
+  void setHorizontalScrollValue(int value);
+  void setVerticalScrollValue(int value);
 };
 
 void popdown_science_report();