Added second implementation of flexible scroll with event filter.

23rd · 23rd · commit 99567d3a5323 · 2025-11-06T23:47:03.000+03:00
diff --git a/Telegram/SourceFiles/info/info_flexible_scroll.cpp b/Telegram/SourceFiles/info/info_flexible_scroll.cpp
@@ -8,6 +8,7 @@ For license and copyright information please follow this link:
 #include "info/info_flexible_scroll.h"
 
 #include "ui/widgets/scroll_area.h"
+#include "base/event_filter.h"
 #include "styles/style_info.h"
 
 #include <QtWidgets/QApplication>
@@ -29,7 +30,8 @@ FlexibleScrollHelper::FlexibleScrollHelper(
 , _setViewport(setViewport)
 , _data(data) {
 	setupScrollAnimation();
-	setupScrollHandling();
+	// setupScrollHandling();
+	setupScrollHandlingWithFilter();
 }
 
 void FlexibleScrollHelper::setupScrollAnimation() {
@@ -195,4 +197,130 @@ void FlexibleScrollHelper::setupScrollHandling() {
 	}));
 }
 
+void FlexibleScrollHelper::setupScrollHandlingWithFilter() {
+	const auto heightDiff = [=] {
+		return _pinnedToTop->maximumHeight()
+			- _pinnedToTop->minimumHeight();
+	};
+
+	rpl::combine(
+		_pinnedToTop->heightValue(),
+		_inner->heightValue()
+	) | rpl::start_with_next([=](int, int h) {
+		_data.contentHeightValue.fire(h + heightDiff());
+	}, _pinnedToTop->lifetime());
+
+	const auto singleStep = _scroll->verticalScrollBar()->singleStep()
+		* QApplication::wheelScrollLines();
+	const auto step1 = (_pinnedToTop->maximumHeight()
+			< st::infoProfileTopBarHeightMax)
+		? (st::infoProfileTopBarStep2 + st::lineWidth)
+		: st::infoProfileTopBarStep1;
+	const auto step2 = st::infoProfileTopBarStep2;
+
+	base::install_event_filter(_scroll->verticalScrollBar(), [=](
+			not_null<QEvent*> e) {
+		if (e->type() != QEvent::Wheel) {
+			return base::EventFilterResult::Continue;
+		}
+		const auto wheel = static_cast<QWheelEvent*>(e.get());
+		const auto delta = wheel->angleDelta().y();
+		if (std::abs(delta) != 120) {
+			return base::EventFilterResult::Continue;
+		}
+		const auto top = _scroll->scrollTop();
+		const auto diff = (delta > 0) ? -singleStep : singleStep;
+		const auto previousValue = top;
+		const auto targetTop = top + diff;
+		const auto nextStep = (diff > 0)
+			? ((previousValue == 0)
+				? step1
+				: (previousValue == step1)
+				? step2
+				: -1)
+			: ((targetTop < step1)
+				? 0
+				: (targetTop < step2)
+				? step1
+				: -1);
+		if (_scrollAnimation.animating()
+			&& ((_scrollTopTo > _scrollTopFrom) != (diff > 0))) {
+			auto overriddenDirection = true;
+			if (_scrollTopTo > _scrollTopFrom) {
+				if (_scrollTopTo == step1) {
+					_scrollTopTo = 0;
+				} else if (_scrollTopTo == step2) {
+					_scrollTopTo = step1;
+				} else {
+					overriddenDirection = false;
+				}
+			} else {
+				if (_scrollTopTo == 0) {
+					_scrollTopTo = step1;
+				} else if (_scrollTopTo == step1) {
+					_scrollTopTo = step2;
+				} else {
+					overriddenDirection = false;
+				}
+			}
+			if (overriddenDirection) {
+				_timeOffset = crl::now() - _scrollAnimation.started();
+				_scrollTopFrom = _lastScrollApplied
+					? _lastScrollApplied
+					: top;
+				return base::EventFilterResult::Cancel;
+			} else {
+				_scrollAnimation.stop();
+				_scrollTopFrom = 0;
+				_scrollTopTo = 0;
+				_timeOffset = 0;
+				_lastScrollApplied = 0;
+			}
+		}
+		_scrollTopFrom = _lastScrollApplied ? _lastScrollApplied : top;
+		if (!_scrollAnimation.animating()) {
+			_scrollTopTo = (nextStep != -1) ? nextStep : targetTop;
+			_scrollAnimation.start();
+		} else {
+			if (_scrollTopTo > _scrollTopFrom) {
+				if (_scrollTopTo == step1) {
+					_scrollTopTo = step2;
+				} else {
+					_scrollTopTo += diff;
+				}
+			} else {
+				if (_scrollTopTo == step2) {
+					_scrollTopTo = step1;
+				} else if (_scrollTopTo == step1) {
+					_scrollTopTo = 0;
+				} else {
+					_scrollTopTo += diff;
+				}
+			}
+			_timeOffset = crl::now() - _scrollAnimation.started();
+		}
+		return base::EventFilterResult::Cancel;
+	}, _filterLifetime);
+
+	_scroll->scrollTopValue(
+	) | rpl::start_with_next([=](int top) {
+		const auto current = heightDiff() - top;
+		_inner->moveToLeft(0, std::min(0, current));
+		_pinnedToTop->resize(
+			_pinnedToTop->width(),
+			std::max(current + _pinnedToTop->minimumHeight(), 0));
+	}, _inner->lifetime());
+
+	_data.fillerWidthValue.events(
+	) | rpl::start_with_next([=](int w) {
+		_inner->resizeToWidth(w);
+	}, _inner->lifetime());
+
+	_setPaintPadding({ 0, _pinnedToTop->minimumHeight(), 0, 0 });
+	_setViewport(_pinnedToTop->events(
+	) | rpl::filter([](not_null<QEvent*> e) {
+		return e->type() == QEvent::Wheel;
+	}));
+}
+
 } // namespace Info
diff --git a/Telegram/SourceFiles/info/info_flexible_scroll.h b/Telegram/SourceFiles/info/info_flexible_scroll.h
@@ -31,6 +31,7 @@ class FlexibleScrollHelper final {
 private:
 	void setupScrollAnimation();
 	void setupScrollHandling();
+	void setupScrollHandlingWithFilter();
 
 	const not_null<Ui::ScrollArea*> _scroll;
 	const not_null<Ui::RpWidget*> _inner;
@@ -46,6 +47,7 @@ class FlexibleScrollHelper final {
 	int _lastScrollApplied = 0;
 	int _scrollTopPrevious = 0;
 	bool _applyingFakeScrollState = false;
+	rpl::lifetime _filterLifetime;
 };
 
 } // namespace Info
