chatgui: add scroll-to-bottom floating button, incremental message refresh via getMessagesSince

tools/chatgui/src/chatview.cpp

@@ -6,11 +6,38 @@
 #include <QDebug>
 #include <QMouseEvent>
 #include <QKeyEvent>
+#include <QScrollBar>
 
 ChatView::ChatView(QWidget *parent)
     : QListView(parent)
 {
     setMouseTracking(true);
+
+    m_scrollDownBtn = new QPushButton(QStringLiteral("\u25BC"), this);
+    m_scrollDownBtn->setFixedSize(36, 36);
+    m_scrollDownBtn->setCursor(Qt::PointingHandCursor);
+    m_scrollDownBtn->setStyleSheet(
+        "QPushButton {"
+        "  background: rgba(60,60,60,180);"
+        "  color: #ffffff;"
+        "  border: none;"
+        "  border-radius: 18px;"
+        "  font-size: 16px;"
+        "}"
+        "QPushButton:hover {"
+        "  background: rgba(90,90,90,220);"
+        "}"
+    );
+    m_scrollDownBtn->setToolTip(tr("Scroll to bottom"));
+    m_scrollDownBtn->setVisible(false);
+
+    connect(m_scrollDownBtn, &QPushButton::clicked, this, [this]() {
+        scrollToBottom();
+    });
+    connect(verticalScrollBar(), &QScrollBar::valueChanged, this, &ChatView::updateScrollDownBtn);
+    connect(verticalScrollBar(), &QScrollBar::rangeChanged, this, &ChatView::updateScrollDownBtn);
+
+    m_scrollDownBtn->raise();
 }
 
 void ChatView::setBackgroundImage(const QString &path) {
@@ -24,6 +51,7 @@ void ChatView::setBackgroundImage(const QString &path) {
 void ChatView::resizeEvent(QResizeEvent *event) {
     QListView::resizeEvent(event);
     scheduleDelayedItemsLayout();
+    updateScrollDownBtn();
 }
 
 void ChatView::scrollContentsBy(int dx, int dy) {
@@ -150,3 +178,14 @@ void ChatView::copySelection() {
         QApplication::clipboard()->setText(r);
     }
 }
+
+void ChatView::updateScrollDownBtn() {
+    QScrollBar* sb = verticalScrollBar();
+    bool atBottom = sb && (sb->value() >= sb->maximum());
+    m_scrollDownBtn->setVisible(!atBottom);
+    if (!atBottom) {
+        QRect vr = viewport()->geometry();
+        m_scrollDownBtn->move(vr.right() - 44, vr.bottom() - 44);
+        m_scrollDownBtn->raise();
+    }
+}