Improve initial visible scroll handling.

Telegram/SourceFiles/history/history_inner_widget.cpp

@@ -458,6 +458,14 @@ HistoryInner::HistoryInner(
 	) | rpl::on_next(
 		[this](auto item) { itemRemoved(item); },
 		lifetime());
+	session().data().newItemAdded(
+	) | rpl::filter([=](not_null<HistoryItem*> item) {
+		const auto history = item->history();
+		return (history == _history)
+			|| (_migrated && history == _migrated);
+	}) | rpl::on_next([=] {
+		checkAnnounceFirstMessages();
+	}, lifetime());
 	setupThanosEffect();
 	session().data().viewRemoved(
 	) | rpl::on_next(
@@ -840,13 +848,7 @@ void HistoryInner::messagesReceived(
 			_migrated->addNewerSlice(QVector<MTPMessage>());
 		}
 	}
-	if (_announceFirstMessages && hasFocus()) {
-		InvokeQueued(this, [=] {
-			if (_announceFirstMessages && hasFocus()) {
-				announceAccessibilityFocusedChild();
-			}
-		});
-	}
+	checkAnnounceFirstMessages();
 }
 
 void HistoryInner::messagesReceivedDown(
@@ -6626,17 +6628,30 @@ auto HistoryInner::computeActiveColumns(int row) const
 	return _activeColumns;
 }
 
+void HistoryInner::checkAnnounceFirstMessages() {
+	if (_announceFirstMessages && hasFocus()) {
+		InvokeQueued(this, [=] {
+			if (_announceFirstMessages && hasFocus()) {
+				announceAccessibilityFocusedChild();
+			}
+		});
+	}
+}
+
 void HistoryInner::announceAccessibilityFocusedChild() {
 	const auto count = accessibilityChildCount();
 	if (count <= 0) {
-		// One-shot for chats focused before their first page arrived:
+		// One-shot for chats focused before their first messages arrived:
 		// while the empty list holds focus, remember that the first
-		// received slice should announce the focused message. Fired
-		// (queued) from messagesReceived and disarmed by any real
-		// announcement below or in a later focus-in.
-		if (Ui::ScreenReaderModeActive()) {
-			_announceFirstMessages = true;
-		}
+		// received slice (or the first live-added message in a genuinely
+		// empty chat) should announce the focused message. Fired (queued)
+		// from checkAnnounceFirstMessages and disarmed by any real
+		// announcement below or in a later focus-in. Deliberately not
+		// gated by the screen-reader-mode detector: it may still be false
+		// during startup or for valid clients that are not on its
+		// allowlist, while the deferred announcement is a no-op without
+		// an accessibility client and never moves ordinary keyboard focus.
+		_announceFirstMessages = true;
 		return;
 	}
 	_announceFirstMessages = false;

Telegram/SourceFiles/history/history_inner_widget.h

@@ -323,6 +323,7 @@ private:
 	void playPauseFocusedMedia();
 	void setAccessibilityFocusedItem(int index, HistoryItem *item);
 	void announceAccessibilityFocus(int index);
+	void checkAnnounceFirstMessages();
 	void announceAccessibilityFocusedChild();
 	void applyAccessibilityFocus(int index, bool announceAlways);
 	[[nodiscard]] auto computeActiveColumns(int row) const

Telegram/SourceFiles/history/history_widget.cpp

@@ -393,7 +393,9 @@ HistoryWidget::HistoryWidget(
 	}), lifetime());
 
 	_scroll->setBottomContentRequest([=] {
-		if (!_history || !_history->loadedAtBottom()) {
+		if (!_history
+			|| _firstLoadRequest
+			|| !_history->loadedAtBottom()) {
 			return false;
 		}
 		using Result = Data::SponsoredMessages::AppendResult;
@@ -4797,6 +4799,8 @@ void HistoryWidget::loadMessages() {
 bool HistoryWidget::historyLoadedAtTop() const {
 	if (!_history) {
 		return true;
+	} else if (_firstLoadRequest) {
+		return false;
 	}
 	const auto loadMigrated = _migrated
 		&& (_history->isEmpty()
@@ -4807,8 +4811,16 @@ bool HistoryWidget::historyLoadedAtTop() const {
 }
 
 bool HistoryWidget::historyLoadedAtBottom() const {
+	// While the first load request is pending the (visible) scroll area
+	// shows a blank list, but getReadyFor() may have already marked the
+	// history as loaded at bottom before any server page arrived. Report
+	// unloaded edges for that interval: it keeps the elastic overscroll
+	// (and the pull-to-next-channel gesture riding on it) away from the
+	// blank list until the requested messages are actually shown.
 	if (!_history) {
 		return true;
+	} else if (_firstLoadRequest) {
+		return false;
 	}
 	const auto loadMigrated = _migrated
 		&& !(_migrated->isEmpty()
@@ -8109,12 +8121,11 @@ void HistoryWidget::updateHistoryGeometry(
 	});
 	if (!_history
 		|| (initial && _historyInited)
-		|| (!initial && !_historyInited)) {
+		|| (!initial && !_historyInited && !_firstLoadRequest)) {
 		return;
 	}
-	if (_firstLoadRequest || _showAnimation) {
+	if (_showAnimation) {
 		_updateHistoryGeometryRequired = true;
-		// scrollTopMax etc are not working after recountHistoryGeometry()
 		return;
 	}
 
@@ -8211,6 +8222,16 @@ void HistoryWidget::updateHistoryGeometry(
 		_subsectionTabs->setBoundingRect(
 			{ 0, subsectionTabsTop, width(), areaHeight });
 	}
+	if (_firstLoadRequest) {
+		// The scroll area stays visible (and possibly focused) while the
+		// first messages are being loaded, so its viewport geometry above
+		// is maintained even now. The list layout and the scroll position
+		// are still deferred until the requested messages arrive:
+		// scrollTopMax etc are not working after recountHistoryGeometry()
+		// and the initial scroll position can not be counted yet.
+		_updateHistoryGeometryRequired = true;
+		return;
+	}
 
 	updateListSize();
 	_updateHistoryGeometryRequired = false;