From a21b6d7416c0899a5622a1c3f6087cbdf0064538 Mon Sep 17 00:00:00 2001
From: John Preston <johnprestonmail@gmail.com>
Date: Mon, 2 Nov 2020 11:44:05 +0300
Subject: [PATCH] Fix restoring scroll state with a pinned bar.

---
 Telegram/SourceFiles/history/history_widget.cpp | 6 +++++-
 Telegram/SourceFiles/history/history_widget.h   | 1 +
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/Telegram/SourceFiles/history/history_widget.cpp b/Telegram/SourceFiles/history/history_widget.cpp
index db142d165..11aa0bd02 100644
--- a/Telegram/SourceFiles/history/history_widget.cpp
+++ b/Telegram/SourceFiles/history/history_widget.cpp
@@ -3230,6 +3230,9 @@ void HistoryWidget::doneShow() {
 	} else {
 		handlePendingHistoryUpdate();
 	}
+	// If we show pinned bar here, we don't want it to change the
+	// calculated and prepared scrollTop of the messages history.
+	_preserveScrollTop = true;
 	preloadHistoryIfNeeded();
 	updatePinnedViewer();
 	if (_pinnedBar) {
@@ -3237,6 +3240,7 @@ void HistoryWidget::doneShow() {
 	}
 	checkHistoryActivation();
 	App::wnd()->setInnerFocus();
+	_preserveScrollTop = false;
 }
 
 void HistoryWidget::finishAnimating() {
@@ -5330,7 +5334,7 @@ void HistoryWidget::checkPinnedBarState() {
 	_pinnedBarHeight = 0;
 	_pinnedBar->heightValue(
 	) | rpl::start_with_next([=](int height) {
-		_topDelta = (height - _pinnedBarHeight);
+		_topDelta = _preserveScrollTop ? 0 : (height - _pinnedBarHeight);
 		_pinnedBarHeight = height;
 		updateHistoryGeometry();
 		updateControlsGeometry();
diff --git a/Telegram/SourceFiles/history/history_widget.h b/Telegram/SourceFiles/history/history_widget.h
index 7242417fc..b2b1220b4 100644
--- a/Telegram/SourceFiles/history/history_widget.h
+++ b/Telegram/SourceFiles/history/history_widget.h
@@ -599,6 +599,7 @@ private:
 	std::unique_ptr<HistoryView::PinnedTracker> _pinnedTracker;
 	std::unique_ptr<Ui::PinnedBar> _pinnedBar;
 	int _pinnedBarHeight = 0;
+	bool _preserveScrollTop = false;
 	FullMsgId _pinnedClickedId;
 	std::optional<FullMsgId> _minPinnedId;