Added utils for fade animated showing/hiding of widgets.

CMakeLists.txt

@@ -58,6 +58,8 @@ PRIVATE
     ui/effects/radial_animation.h
     ui/effects/ripple_animation.cpp
     ui/effects/ripple_animation.h
+    ui/effects/show_animation.cpp
+    ui/effects/show_animation.h
     ui/effects/slide_animation.cpp
     ui/effects/slide_animation.h
     ui/gl/gl_detection.cpp

ui/effects/show_animation.cpp

@@ -0,0 +1,110 @@
+// This file is part of Desktop App Toolkit,
+// a set of libraries for developing nice desktop applications.
+//
+// For license and copyright information please follow this link:
+// https://github.com/desktop-app/legal/blob/master/LEGAL
+//
+#include "ui/effects/show_animation.h"
+
+#include "ui/effects/animations.h"
+#include "ui/rp_widget.h"
+#include "styles/style_widgets.h"
+
+namespace Ui::Animations {
+namespace {
+
+void AnimateWidgets(const Widgets &targets, bool show) {
+	enum class Finish {
+		Bad,
+		Good,
+	};
+	struct Object {
+		base::unique_qptr<Ui::RpWidget> container;
+		QPointer<Ui::RpWidget> weakTarget;
+	};
+	struct State {
+		rpl::event_stream<Finish> destroy;
+		Ui::Animations::Simple animation;
+		std::vector<Object> objects;
+	};
+	auto lifetime = std::make_shared<rpl::lifetime>();
+	const auto state = lifetime->make_state<State>();
+
+	const auto from = show ? 0. : 1.;
+	const auto to = show ? 1. : 0.;
+
+	for (const auto &target : targets) {
+		state->objects.push_back({
+			base::make_unique_q<Ui::RpWidget>(target->parentWidget()),
+			Ui::MakeWeak(target),
+		});
+
+		const auto pixmap = Ui::GrabWidget(target);
+		const auto raw = state->objects.back().container.get();
+
+		raw->paintRequest(
+		) | rpl::start_with_next([=] {
+			QPainter p(raw);
+
+			p.setOpacity(state->animation.value(to));
+			p.drawPixmap(QPoint(), pixmap);
+		}, raw->lifetime());
+
+		target->geometryValue(
+		) | rpl::start_with_next([=](const QRect &r) {
+			raw->setGeometry(r);
+		}, raw->lifetime());
+
+		raw->show();
+
+		if (!show) {
+			target->hide();
+		}
+	}
+
+	state->destroy.events(
+	) | rpl::take(
+		1
+	) | rpl::start_with_next([=](Finish type) mutable {
+		if (type == Finish::Good && show) {
+			for (const auto &object : state->objects) {
+				if (object.weakTarget) {
+					object.weakTarget->show();
+				}
+			}
+		}
+		if (lifetime) {
+			base::take(lifetime)->destroy();
+		}
+	}, *lifetime);
+
+	state->animation.start(
+		[=](auto value) {
+			for (const auto &object : state->objects) {
+				object.container->update();
+
+				if (!object.weakTarget && show) {
+					state->destroy.fire(Finish::Bad);
+					return;
+				}
+			}
+			if (value == to) {
+				state->destroy.fire(Finish::Good);
+			}
+		},
+		from,
+		to,
+		st::defaultToggle.duration);
+}
+
+} // namespace
+
+void ShowWidgets(const Widgets &targets) {
+	AnimateWidgets(targets, true);
+}
+
+void HideWidgets(const Widgets &targets) {
+	AnimateWidgets(targets, false);
+}
+
+} // namespace Ui::Animations

ui/effects/show_animation.h

@@ -0,0 +1,20 @@
+// This file is part of Desktop App Toolkit,
+// a set of libraries for developing nice desktop applications.
+//
+// For license and copyright information please follow this link:
+// https://github.com/desktop-app/legal/blob/master/LEGAL
+//
+#pragma once
+
+namespace Ui {
+class RpWidget;
+} // namespace Ui
+
+namespace Ui::Animations {
+
+using Widgets = std::vector<not_null<Ui::RpWidget*>>;
+
+void ShowWidgets(const Widgets &targets);
+void HideWidgets(const Widgets &targets);
+
+} // namespace Ui::Animations