DolphinQt: avoid scrolling while game list is being modified

Source/Core/DolphinQt/CMakeLists.txt

@@ -320,6 +320,8 @@ add_executable(dolphin-emu
   QtUtils/SignalBlocking.h
   QtUtils/UTF8CodePointCountValidator.cpp
   QtUtils/UTF8CodePointCountValidator.h
+  QtUtils/ViewportLock.cpp
+  QtUtils/ViewportLock.h
   QtUtils/WindowActivationEventFilter.cpp
   QtUtils/WindowActivationEventFilter.h
   QtUtils/WrapInScrollArea.cpp

Source/Core/DolphinQt/GameList/GameList.cpp

@@ -67,6 +67,7 @@
 #include "DolphinQt/QtUtils/ModalMessageBox.h"
 #include "DolphinQt/QtUtils/ParallelProgressDialog.h"
 #include "DolphinQt/QtUtils/SetWindowDecorations.h"
+#include "DolphinQt/QtUtils/ViewportLock.h"
 #include "DolphinQt/Resources.h"
 #include "DolphinQt/Settings.h"
 #include "DolphinQt/WiiUpdate.h"
@@ -116,6 +117,8 @@ GameList::GameList(QWidget* parent) : QStackedWidget(parent), m_model(this)
   connect(&m_model, &QAbstractItemModel::rowsInserted, this, &GameList::ConsiderViewChange);
   connect(&m_model, &QAbstractItemModel::rowsRemoved, this, &GameList::ConsiderViewChange);
 
+  m_viewportLock = new ViewportLock(this, m_list_proxy, m_list);
+
   addWidget(m_list);
   addWidget(m_grid);
   addWidget(m_empty);

Source/Core/DolphinQt/GameList/GameList.h

@@ -20,6 +20,8 @@ namespace UICommon
 class GameFile;
 }
 
+class ViewportLock;
+
 class GameList final : public QStackedWidget
 {
   Q_OBJECT
@@ -100,6 +102,7 @@ private:
   void UpdateFont();
 
   GameListModel m_model;
+  ViewportLock* m_viewportLock;
   QSortFilterProxyModel* m_list_proxy;
   QSortFilterProxyModel* m_grid_proxy;
 

Source/Core/DolphinQt/QtUtils/ViewportLock.cpp

@@ -0,0 +1,34 @@
+// Copyright 2024 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <QAbstractItemModel>
+#include <QAbstractItemView>
+
+#include "DolphinQt/QtUtils/ViewportLock.h"
+
+ViewportLock::ViewportLock(QObject* parent, QAbstractItemModel* model, QAbstractItemView* view)
+    : QObject(parent), m_view(view)
+{
+  connect(model, &QAbstractItemModel::rowsAboutToBeInserted, this,
+          &ViewportLock::AboutToBeModified);
+  connect(model, &QAbstractItemModel::rowsAboutToBeRemoved, this, &ViewportLock::AboutToBeModified);
+  connect(model, &QAbstractItemModel::rowsInserted, this, &ViewportLock::Modified);
+  connect(model, &QAbstractItemModel::rowsRemoved, this, &ViewportLock::Modified);
+}
+
+void ViewportLock::AboutToBeModified()
+{
+  QSize size = m_view->size();
+  m_first = m_view->indexAt(QPoint(0, 0));
+  m_last = m_view->indexAt(QPoint(size.height(), size.width()));
+}
+
+void ViewportLock::Modified()
+{
+  // Try to keep the first row at the top.
+  // If that fails, try to keep the last row at the bottom.
+  if (m_first.isValid())
+    m_view->scrollTo(m_first, QAbstractItemView::PositionAtTop);
+  else if (m_last.isValid())
+    m_view->scrollTo(m_last, QAbstractItemView::PositionAtBottom);
+}

Source/Core/DolphinQt/QtUtils/ViewportLock.h

@@ -0,0 +1,25 @@
+// Copyright 2024 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include <QObject>
+#include <QPersistentModelIndex>
+
+class QAbstractItemModel;
+class QAbstractItemView;
+
+// Try to keep visible items in view while items are added/removed.
+class ViewportLock : public QObject
+{
+  Q_OBJECT
+
+public:
+  ViewportLock(QObject* parent, QAbstractItemModel* model, QAbstractItemView* view);
+  void AboutToBeModified();
+  void Modified();
+
+private:
+  QAbstractItemView* m_view;
+  QPersistentModelIndex m_first, m_last;
+};