From 119a22bc8b5b263356dfefd1a41c17d57337c8e5 Mon Sep 17 00:00:00 2001
From: "J.D. Purcell" <jdpurcell@gmail.com>
Date: Sun, 18 Feb 2024 15:57:33 -0500
Subject: [PATCH] Use Qt's built-in animation for constrained positioning

Works mostly the same, but since the movement is absolute instead of relative it handles interruptions (user panning during animation) differently. I prefer the relative behavior so won't end up using this, but saving it for reference.
---
 src/scrollhelper.cpp | 55 +++++++++++++++-----------------------------
 src/scrollhelper.h   | 16 ++++---------
 2 files changed, 23 insertions(+), 48 deletions(-)

diff --git a/src/scrollhelper.cpp b/src/scrollhelper.cpp
index 661a927d..70ea7071 100644
--- a/src/scrollhelper.cpp
+++ b/src/scrollhelper.cpp
@@ -8,11 +8,12 @@ ScrollHelper::ScrollHelper(QAbstractScrollArea *parent, GetParametersCallback ge
     vScrollBar = parent->verticalScrollBar();
     this->getParametersCallback = getParametersCallback;
 
-    animatedScrollTimer = new QTimer(this);
-    animatedScrollTimer->setSingleShot(true);
-    animatedScrollTimer->setTimerType(Qt::PreciseTimer);
-    animatedScrollTimer->setInterval(10);
-    connect(animatedScrollTimer, &QTimer::timeout, this, [this]{ handleAnimatedScroll(); });
+    scrollAnimation = new QVariantAnimation(this);
+    scrollAnimation->setDuration(animatedScrollDuration);
+    scrollAnimation->setEasingCurve(QEasingCurve::OutCirc);
+    connect(scrollAnimation, &QVariantAnimation::valueChanged, this, [this](const QVariant &value) {
+        setScrollPosition(value.toPoint());
+    });
 }
 
 void ScrollHelper::move(QPointF delta)
@@ -44,7 +45,7 @@ void ScrollHelper::move(QPointF delta)
         vMin,
         vMax
     );
-    QPointF scrollLocation = QPointF(hScrollBar->value(), vScrollBar->value()) + lastMoveRoundingError;
+    QPointF scrollLocation = getScrollPosition() + lastMoveRoundingError;
     qreal scrollDeltaX = delta.x();
     qreal scrollDeltaY = delta.y();
     if (p.shouldConstrain)
@@ -75,48 +76,35 @@ void ScrollHelper::constrain(bool skipAnimation)
     move(QPointF());
 
     if (skipAnimation)
-        applyScrollDelta(-overscrollDistance);
+        setScrollPosition(getScrollPosition() - overscrollDistance);
     else
         beginAnimatedScroll(-overscrollDistance);
 }
 
 void ScrollHelper::cancelAnimation()
 {
-    animatedScrollTimer->stop();
+    scrollAnimation->stop();
 }
 
 void ScrollHelper::beginAnimatedScroll(QPoint delta)
 {
     if (delta.isNull())
         return;
-    animatedScrollTotalDelta = delta;
-    animatedScrollAppliedDelta = {};
-    animatedScrollElapsed.start();
-    animatedScrollTimer->start();
+    QPoint startPos = getScrollPosition();
+    scrollAnimation->setStartValue(startPos);
+    scrollAnimation->setEndValue(startPos + delta);
+    scrollAnimation->start();
 }
 
-void ScrollHelper::handleAnimatedScroll()
+QPoint ScrollHelper::getScrollPosition()
 {
-    qreal elapsed = animatedScrollElapsed.elapsed();
-    if (elapsed >= animatedScrollDuration)
-    {
-        applyScrollDelta(animatedScrollTotalDelta - animatedScrollAppliedDelta);
-    }
-    else
-    {
-        QPoint intermediateDelta = animatedScrollTotalDelta * smoothAnimation(elapsed / animatedScrollDuration);
-        applyScrollDelta(intermediateDelta - animatedScrollAppliedDelta);
-        animatedScrollAppliedDelta = intermediateDelta;
-        animatedScrollTimer->start();
-    }
+    return QPoint(hScrollBar->value(), vScrollBar->value());
 }
 
-void ScrollHelper::applyScrollDelta(QPoint delta)
+void ScrollHelper::setScrollPosition(QPoint pos)
 {
-    if (delta.x() != 0)
-        hScrollBar->setValue(hScrollBar->value() + delta.x());
-    if (delta.y() != 0)
-        vScrollBar->setValue(vScrollBar->value() + delta.y());
+    hScrollBar->setValue(pos.x());
+    vScrollBar->setValue(pos.y());
 }
 
 void ScrollHelper::calculateScrollRange(int contentDimension, int viewportDimension, int offset, bool shouldCenter, int &minValue, int &maxValue)
@@ -154,10 +142,3 @@ qreal ScrollHelper::calculateScrollDelta(qreal currentValue, int minValue, int m
     }
     return proposedDelta;
 }
-
-// Converts linear motion from [0,1] into something that looks more natural. Derived from the
-// formula for a circle, i.e. the graph of this is literally the top-left quarter of a circle.
-qreal ScrollHelper::smoothAnimation(qreal x)
-{
-    return qPow(1.0 - qPow(x - 1.0, 2.0), 0.5);
-}
diff --git a/src/scrollhelper.h b/src/scrollhelper.h
index 6e3193cd..dc78464b 100644
--- a/src/scrollhelper.h
+++ b/src/scrollhelper.h
@@ -2,9 +2,8 @@
 #define SCROLLHELPER_H
 
 #include <QAbstractScrollArea>
-#include <QElapsedTimer>
 #include <QScrollBar>
-#include <QTimer>
+#include <QVariantAnimation>
 
 class ScrollHelper : public QObject
 {
@@ -31,27 +30,22 @@ class ScrollHelper : public QObject
 private:
     void beginAnimatedScroll(QPoint delta);
 
-    void handleAnimatedScroll();
+    QPoint getScrollPosition();
 
-    void applyScrollDelta(QPoint delta);
+    void setScrollPosition(QPoint pos);
 
     static void calculateScrollRange(int contentDimension, int viewportDimension, int offset, bool shouldCenter, int &minValue, int &maxValue);
 
     static qreal calculateScrollDelta(qreal currentValue, int minValue, int maxValue, qreal proposedDelta);
 
-    static qreal smoothAnimation(qreal x);
-
     QScrollBar *hScrollBar;
     QScrollBar *vScrollBar;
     GetParametersCallback getParametersCallback;
     QPointF lastMoveRoundingError;
     QPoint overscrollDistance;
 
-    QTimer *animatedScrollTimer;
-    QPoint animatedScrollTotalDelta;
-    QPoint animatedScrollAppliedDelta;
-    QElapsedTimer animatedScrollElapsed;
-    const qreal animatedScrollDuration {250.0};
+    QVariantAnimation *scrollAnimation;
+    const int animatedScrollDuration {250};
 };
 
 #endif // SCROLLHELPER_H