flick velocity and deceleration

Plugins/ZShell/Components/carouselview.hpp

@@ -10,6 +10,8 @@
 #include <QVariantAnimation>
 #include <QVariantList>
 #include <QVector>
+#include <qtypes.h>
+#include <qvectornd.h>
 
 namespace ZShell::components {
 
@@ -150,6 +152,11 @@ class CarouselView : public QQuickItem {
 		bool active = false;
 	};
 
+	struct VelocitySample {
+		qint64 t;
+		qreal x;
+	};
+
 	void rebuildArrangement();
 	void relayout();
 
@@ -190,6 +197,9 @@ class CarouselView : public QQuickItem {
 	QQuickItem* acquireItem();
 	void releaseAllItems();
 
+	void addVelocitySample(qint64 t, qreal x);
+	qreal sampledVelocity() const;
+
 	QQmlComponent* m_delegate = nullptr;
 	QVariantList m_model;
 	QVariantMap m_delegateProperties;
@@ -226,9 +236,9 @@ class CarouselView : public QQuickItem {
 	qreal m_pressContentX = 0;
 
 	QElapsedTimer m_dragTimer;
-	qreal m_lastMoveX = 0;
-	qint64 m_lastMoveT = 0;
-	qreal m_velocity = 0;
+
+	QVector<VelocitySample> m_velocitySamples;
+	static constexpr qint64 kVelocitySampleWindowMs = 80;
 
 	QVariantAnimation* m_flickAnim = nullptr;