From 3d8b303ab71dcacb2e42e8dc13cfa5b2c7590561 Mon Sep 17 00:00:00 2001
From: John Preston <johnprestonmail@gmail.com>
Date: Wed, 12 Jan 2022 14:41:33 +0300
Subject: [PATCH] Implement parabolic reaction drop.

---
 .../view/history_view_react_animation.cpp     | 47 +++++++++++++++++--
 .../view/history_view_react_animation.h       |  5 ++
 Telegram/SourceFiles/ui/chat/chat.style       |  1 +
 3 files changed, 50 insertions(+), 3 deletions(-)

diff --git a/Telegram/SourceFiles/history/view/history_view_react_animation.cpp b/Telegram/SourceFiles/history/view/history_view_react_animation.cpp
index c715d5ddf8..58857bb121 100644
--- a/Telegram/SourceFiles/history/view/history_view_react_animation.cpp
+++ b/Telegram/SourceFiles/history/view/history_view_react_animation.cpp
@@ -12,11 +12,12 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 #include "data/data_message_reactions.h"
 #include "data/data_document.h"
 #include "data/data_document_media.h"
+#include "styles/style_chat.h"
 
 namespace HistoryView::Reactions {
 namespace {
 
-constexpr auto kFlyDuration = crl::time(200);
+constexpr auto kFlyDuration = crl::time(300);
 
 } // namespace
 
@@ -67,7 +68,10 @@ SendAnimation::SendAnimation(
 
 SendAnimation::~SendAnimation() = default;
 
-QRect SendAnimation::paintGetArea(QPainter &p, QPoint origin, QRect target) const {
+QRect SendAnimation::paintGetArea(
+		QPainter &p,
+		QPoint origin,
+		QRect target) const {
 	if (!_flyIcon) {
 		p.drawImage(target, _center->frame());
 		const auto wide = QRect(
@@ -84,7 +88,7 @@ QRect SendAnimation::paintGetArea(QPainter &p, QPoint origin, QRect target) cons
 	const auto progress = _fly.value(1.);
 	const auto rect = QRect(
 		anim::interpolate(from.x(), target.x(), progress),
-		anim::interpolate(from.y(), target.y(), progress),
+		computeParabolicTop(from.y(), target.y(), progress),
 		anim::interpolate(from.width(), target.width(), progress),
 		anim::interpolate(from.height(), target.height(), progress));
 	const auto wide = rect.marginsAdded(margins);
@@ -101,6 +105,43 @@ QRect SendAnimation::paintGetArea(QPainter &p, QPoint origin, QRect target) cons
 	return wide;
 }
 
+int SendAnimation::computeParabolicTop(
+		int from,
+		int to,
+		float64 progress) const {
+	const auto t = progress;
+	const auto c = from;
+
+	// result = a * t * t + b * t + c
+
+	// y = a * t * t + b * t
+	// shift = y_1 = y(1) = a + b
+	// y_0 = y(t_0) = a * t_0 * t_0 + b * t_0
+	// 0 = 2 * a * t_0 + b
+	// b = y_1 - a
+	// a = y_1 / (1 - 2 * t_0)
+	// b = 2 * t_0 * y_1 / (2 * t_0 - 1)
+	// t_0 = (y_0 / y_1) +- sqrt((y_0 / y_1) * (y_0 / y_1 - 1))
+	const auto y_1 = to - from;
+	if (_cachedKey != y_1) {
+		const auto y_0 = std::min(0, y_1) - st::reactionFlyUp;
+		const auto ratio = y_1 ? (float64(y_0) / y_1) : 0.;
+		const auto root = y_1 ? sqrt(ratio * (ratio - 1)) : 0.;
+		const auto t_0 = !y_1
+			? 0.5
+			: (y_1 > 0)
+			? (ratio + root)
+			: (ratio - root);
+		const auto a = y_1 ? (y_1 / (1 - 2 * t_0)) : (-4 * y_0);
+		const auto b = y_1 - a;
+		_cachedKey = y_1;
+		_cachedA = a;
+		_cachedB = b;
+	}
+
+	return int(base::SafeRound(_cachedA * t * t + _cachedB * t + from));
+}
+
 void SendAnimation::startAnimations() {
 	_center->animate([=] { callback(); }, 0, _center->framesCount() - 1);
 	_effect->animate([=] { callback(); }, 0, _effect->framesCount() - 1);
diff --git a/Telegram/SourceFiles/history/view/history_view_react_animation.h b/Telegram/SourceFiles/history/view/history_view_react_animation.h
index c11864121e..0daca4982c 100644
--- a/Telegram/SourceFiles/history/view/history_view_react_animation.h
+++ b/Telegram/SourceFiles/history/view/history_view_react_animation.h
@@ -42,6 +42,7 @@ private:
 	void flyCallback();
 	void startAnimations();
 	void callback();
+	int computeParabolicTop(int from, int to, float64 progress) const;
 
 	const not_null<::Data::Reactions*> _owner;
 	const QString _emoji;
@@ -53,6 +54,10 @@ private:
 	QRect _flyFrom;
 	bool _valid = false;
 
+	mutable std::optional<int> _cachedKey;
+	mutable float64 _cachedA = 0.;
+	mutable float64 _cachedB = 0.;
+
 };
 
 } // namespace HistoryView::Reactions
diff --git a/Telegram/SourceFiles/ui/chat/chat.style b/Telegram/SourceFiles/ui/chat/chat.style
index 7a1af4f124..c25ce1ab5e 100644
--- a/Telegram/SourceFiles/ui/chat/chat.style
+++ b/Telegram/SourceFiles/ui/chat/chat.style
@@ -991,3 +991,4 @@ reactionGradientFadeSize: 24px;
 reactionAppearStartSkip: 2px;
 reactionMainAppearShift: 20px;
 reactionCollapseFadeThreshold: 40px;
+reactionFlyUp: 50px;