[Chat] Scroll chat view to bottom when loading chat history (#7079)

* [Chat] Scroll chat view to bottom when loading chat history (#2725)

Took 4 minutes


Took 38 seconds

* Harden scrolling to bottom

Took 11 minutes

* Implement stick-to-bottom flag

---------

Co-authored-by: Lukas Brübach <Bruebach.Lukas@bdosecurity.de>

cockatrice/src/interface/widgets/server/chat_view/chat_view.cpp

@@ -13,6 +13,7 @@
 #include <QDesktopServices>
 #include <QMouseEvent>
 #include <QScrollBar>
+#include <QTimer>
 #include <libcockatrice/card/database/card_database_manager.h>
 #include <libcockatrice/network/server/remote/user_level.h>
 #include <libcockatrice/settings/chat_settings.h>
@@ -51,6 +52,9 @@ ChatView::ChatView(TabSupervisor *_tabSupervisor, AbstractGame *_game, bool _sho
     setTextInteractionFlags(Qt::TextSelectableByMouse | Qt::LinksAccessibleByMouse);
     setOpenLinks(false);
     connect(this, &ChatView::anchorClicked, this, &ChatView::openLink);
+
+    connect(verticalScrollBar(), &QScrollBar::rangeChanged, this, &ChatView::onScrollBarRangeChanged);
+    connect(verticalScrollBar(), &QScrollBar::valueChanged, this, &ChatView::onScrollBarValueChanged);
 }
 
 void ChatView::adjustColorsToPalette()
@@ -151,7 +155,7 @@ void ChatView::appendHtml(const QString &html)
     bool atBottom = verticalScrollBar()->value() >= verticalScrollBar()->maximum();
     prepareBlock().insertHtml(html);
     if (atBottom) {
-        verticalScrollBar()->setValue(verticalScrollBar()->maximum());
+        scrollToBottom();
     }
 }
 
@@ -169,7 +173,7 @@ void ChatView::appendHtmlServerMessage(const QString &html, bool optionalIsBold,
 
     prepareBlock().insertHtml(htmlText);
     if (atBottom) {
-        verticalScrollBar()->setValue(verticalScrollBar()->maximum());
+        scrollToBottom();
     }
 }
 
@@ -338,11 +342,36 @@ void ChatView::appendMessage(QString message,
         }
     }
 
-    if (atBottom) {
+    // ChatHistory messages are only ever sent once per room, right after joining, before the user can
+    // interact with the view. Always scroll to the bottom so the whole history is visible on join.
+    if (atBottom || messageType.testFlag(Event_RoomSay::ChatHistory)) {
+        scrollToBottom();
+    }
+}
+
+void ChatView::scrollToBottom()
+{
+    // The document layout, and therefore the scrollbar range, may be updated asynchronously (e.g. while
+    // the chat history is loaded into a view that has not been laid out yet). Setting the value once is
+    // not enough: keep stickToBottom set so any later range change scrolls to the new maximum as well.
+    stickToBottom = true;
+    verticalScrollBar()->setValue(verticalScrollBar()->maximum());
+}
+
+void ChatView::onScrollBarRangeChanged()
+{
+    if (stickToBottom) {
         verticalScrollBar()->setValue(verticalScrollBar()->maximum());
     }
 }
 
+void ChatView::onScrollBarValueChanged(int value)
+{
+    if (value < verticalScrollBar()->maximum()) {
+        stickToBottom = false;
+    }
+}
+
 void ChatView::checkTag(QTextCursor &cursor, QString &message)
 {
     if (message.startsWith("[card]")) {

cockatrice/src/interface/widgets/server/chat_view/chat_view.h

@@ -60,6 +60,7 @@ private:
     QStringList highlightedWords;
     bool evenNumber;
     bool showTimestamps;
+    bool stickToBottom = false;
     HoveredItemType hoveredItemType;
     QString hoveredContent;
     QAction *messageClicked;
@@ -67,6 +68,7 @@ private:
 
     [[nodiscard]] QTextFragment getFragmentUnderMouse(const QPoint &pos) const;
     QTextCursor prepareBlock(bool same = false);
+    void scrollToBottom();
     void appendCardTag(QTextCursor &cursor, const QString &cardName);
     void appendUrlTag(QTextCursor &cursor, QString url);
     static QColor getCustomMentionColor();
@@ -88,6 +90,8 @@ private slots:
     void actMessageClicked();
     void adjustColorsToPalette();
     void refreshBlockColors();
+    void onScrollBarRangeChanged();
+    void onScrollBarValueChanged(int value);
 
 public:
     ChatView(TabSupervisor *_tabSupervisor, AbstractGame *_game, bool _showTimestamps, QWidget *parent = nullptr);