Scroll to active tab in subsection tabs.

Telegram/SourceFiles/history/view/history_view_subsection_tabs.cpp

@@ -234,6 +234,28 @@ void SubsectionTabs::setupSlider(
 		}
 	}, slider->lifetime());
 
+	slider->requestShown(
+	) | rpl::start_with_next([=](Ui::ScrollToRequest request) {
+		const auto full = vertical ? scroll->height() : scroll->width();
+		const auto scrollValue = vertical
+			? scroll->scrollTop()
+			: scroll->scrollLeft();
+		if (request.ymin < scrollValue) {
+			if (vertical) {
+				scroll->scrollToY(request.ymin);
+			} else {
+				scroll->scrollToX(request.ymin);
+			}
+		} else if (request.ymax > scrollValue + full) {
+			const auto value = std::min(request.ymin, request.ymax - full);
+			if (vertical) {
+				scroll->scrollToY(value);
+			} else {
+				scroll->scrollToX(value);
+			}
+		}
+	}, slider->lifetime());
+
 	rpl::merge(
 		scroll->scrolls(),
 		_scrollCheckRequests.events(),

Telegram/SourceFiles/ui/controls/subsection_tabs_slider.cpp

@@ -9,6 +9,7 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 
 #include "dialogs/dialogs_three_state_icon.h"
 #include "ui/effects/ripple_animation.h"
+#include "ui/widgets/scroll_area.h"
 #include "ui/dynamic_image.h"
 #include "ui/unread_badge_paint.h"
 #include "styles/style_chat.h"
@@ -383,24 +384,34 @@ void SubsectionSlider::activate(int index) {
 			}
 		}
 	};
-	const auto weak = Ui::MakeWeak(_bar);
+	const auto weak = MakeWeak(_bar);
 	_sectionActivated.fire_copy(index);
 	if (weak) {
 		const auto duration = st::chatTabsSlider.duration;
 		_activeFrom.start(callback, was.from, now.from, duration);
 		_activeSize.start(callback, was.size, now.size, duration);
+		_requestShown.fire_copy({ now.from, now.from + now.size });
 	}
 }
 
 void SubsectionSlider::setActiveSectionFast(int active) {
 	Expects(active < int(_tabs.size()));
 
+	if (_active == active) {
+		return;
+	}
 	_active = active;
 	_activeFrom.stop();
 	_activeSize.stop();
+	const auto now = getFinalActiveRange();
+	_requestShown.fire({ now.from, now.from + now.size });
 	_bar->update();
 }
 
+rpl::producer<ScrollToRequest> SubsectionSlider::requestShown() const {
+	return _requestShown.events();
+}
+
 int SubsectionSlider::sectionsCount() const {
 	return int(_tabs.size());
 }

Telegram/SourceFiles/ui/controls/subsection_tabs_slider.h

@@ -22,6 +22,7 @@ namespace Ui {
 class DynamicImage;
 class RippleAnimation;
 class SubsectionButton;
+struct ScrollToRequest;
 
 struct SubsectionTab {
 	TextWithEntities text;
@@ -95,6 +96,8 @@ public:
 	Text::MarkedContext buttonContext() override;
 	[[nodiscard]] not_null<SubsectionButton*> buttonAt(int index);
 
+	[[nodiscard]] rpl::producer<ScrollToRequest> requestShown() const;
+
 protected:
 	struct Range {
 		int from = 0;
@@ -137,6 +140,8 @@ protected:
 	rpl::event_stream<int> _sectionContextMenu;
 	Fn<bool()> _paused;
 
+	rpl::event_stream<ScrollToRequest> _requestShown;
+
 };
 
 class VerticalSlider final : public SubsectionSlider {