From d1619b728e89c40c6d66332df50e81f8dabaff97 Mon Sep 17 00:00:00 2001
From: 23rd <23rd@vivaldi.net>
Date: Sat, 28 Mar 2020 17:17:32 +0300
Subject: [PATCH] Added ability to scroll vertical layout during reordering.

---
 ui/wrap/vertical_layout_reorder.cpp | 53 +++++++++++++++++++++++++++--
 ui/wrap/vertical_layout_reorder.h   | 12 ++++++-
 2 files changed, 62 insertions(+), 3 deletions(-)

diff --git a/ui/wrap/vertical_layout_reorder.cpp b/ui/wrap/vertical_layout_reorder.cpp
index e312114..ed97b06 100644
--- a/ui/wrap/vertical_layout_reorder.cpp
+++ b/ui/wrap/vertical_layout_reorder.cpp
@@ -14,9 +14,18 @@
 
 namespace Ui {
 
+namespace {
+
+constexpr auto kScrollFactor = 0.05;
+
+} // namespace
+
 VerticalLayoutReorder::VerticalLayoutReorder(
-	not_null<VerticalLayout*> layout)
-: _layout(layout) {
+	not_null<VerticalLayout*> layout,
+	not_null<ScrollArea*> scroll)
+: _layout(layout)
+, _scroll(scroll)
+, _scrollAnimation([=] { updateScrollCallback(); }) {
 }
 
 void VerticalLayoutReorder::cancel() {
@@ -100,6 +109,8 @@ void VerticalLayoutReorder::updateOrder(int index, QPoint position) {
 	current.shift = current.finalShift = shift;
 	_layout->setVerticalShift(index, shift);
 
+	checkForScrollAnimation();
+
 	const auto count = _entries.size();
 	const auto currentHeight = current.widget->height();
 	const auto currentMiddle = current.widget->y() + currentHeight / 2;
@@ -153,6 +164,7 @@ void VerticalLayoutReorder::mouseRelease(
 	if (button != Qt::LeftButton) {
 		return;
 	}
+	_scrollAnimation.stop();
 	finishCurrent();
 }
 
@@ -267,4 +279,41 @@ auto VerticalLayoutReorder::updates() const -> rpl::producer<Single> {
 	return _updates.events();
 }
 
+void VerticalLayoutReorder::updateScrollCallback() {
+	const auto delta = deltaFromEdge();
+	const auto oldTop = _scroll->scrollTop();
+	_scroll->scrollToY(oldTop + delta);
+	const auto newTop = _scroll->scrollTop();
+
+	_currentStart += oldTop - newTop;
+	if (newTop == 0 || newTop == _scroll->scrollTopMax()) {
+		_scrollAnimation.stop();
+	}
+}
+
+void VerticalLayoutReorder::checkForScrollAnimation() {
+	if (!deltaFromEdge() || _scrollAnimation.animating()) {
+		return;
+	}
+	_scrollAnimation.start();
+}
+
+int VerticalLayoutReorder::deltaFromEdge() {
+	Expects(_currentWidget != nullptr);
+
+	const auto globalPosition = _currentWidget->mapToGlobal(QPoint(0, 0));
+	const auto localTop = _scroll->mapFromGlobal(globalPosition).y();
+	const auto localBottom = localTop
+		+ _currentWidget->height()
+		- _scroll->height();
+
+	const auto isTopEdge = (localTop < 0);
+	const auto isBottomEdge = (localBottom > 0);
+	if (!isTopEdge && !isBottomEdge) {
+		_scrollAnimation.stop();
+		return 0;
+	}
+	return int((isBottomEdge ? localBottom : localTop) * kScrollFactor);
+}
+
 } // namespace Ui
diff --git a/ui/wrap/vertical_layout_reorder.h b/ui/wrap/vertical_layout_reorder.h
index d5e6769..27e62af 100644
--- a/ui/wrap/vertical_layout_reorder.h
+++ b/ui/wrap/vertical_layout_reorder.h
@@ -7,6 +7,7 @@
 #pragma once
 
 #include "ui/effects/animations.h"
+#include "ui/widgets/scroll_area.h"
 
 namespace Ui {
 
@@ -27,7 +28,9 @@ public:
 		State state = State::Started;
 	};
 
-	VerticalLayoutReorder(not_null<VerticalLayout*> layout);
+	VerticalLayoutReorder(
+		not_null<VerticalLayout*> layout,
+		not_null<ScrollArea*> scroll);
 
 	void start();
 	void cancel();
@@ -59,7 +62,14 @@ private:
 	void moveToShift(int index, int shift);
 	void updateShift(not_null<RpWidget*> widget, int indexHint);
 
+	void updateScrollCallback();
+	void checkForScrollAnimation();
+	int deltaFromEdge();
+
 	const not_null<Ui::VerticalLayout*> _layout;
+	const not_null<Ui::ScrollArea*> _scroll;
+
+	Ui::Animations::Basic _scrollAnimation;
 
 	RpWidget *_currentWidget = nullptr;
 	int _currentStart = 0;