Cached peer list rows into opaque images while scrolling.

Telegram/SourceFiles/boxes/peer_list_scroll_cache.cpp

@@ -0,0 +1,33 @@
+/*
+This file is part of Telegram Desktop,
+the official desktop application for the Telegram messaging service.
+
+For license and copyright information please follow this link:
+https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
+*/
+#include "boxes/peer_list_scroll_cache.h"
+
+namespace {
+
+constexpr auto kStopTimeout = crl::time(120);
+
+} // namespace
+
+PeerListRowsScrollCache::PeerListRowsScrollCache(Fn<void()> stopped) {
+	_stopTimer.setCallback([=] {
+		_scrolling = false;
+		_images.clear();
+		stopped();
+	});
+}
+
+void PeerListRowsScrollCache::markScrolling() {
+	_scrolling = true;
+	_stopTimer.callOnce(kStopTimeout);
+}
+
+void PeerListRowsScrollCache::invalidate(uint64 rowId) {
+	if (const auto i = _images.find(rowId); i != end(_images)) {
+		_images.erase(i);
+	}
+}