From 792ff844192c8ce43b938af41c79213eb57dac75 Mon Sep 17 00:00:00 2001
From: Vladimir Zolotopupov <zvova7890@gmail.com>
Date: Mon, 21 Aug 2023 23:01:11 +0300
Subject: [PATCH] wayland: Refactor the high-resolution scroll wheel step
 accumulator

---
 src/wayland/pointer_interface.cpp | 41 +++++++++++++------------------
 src/wayland/pointer_interface_p.h | 30 ++++++++++++++++++++--
 2 files changed, 45 insertions(+), 26 deletions(-)

diff --git a/src/wayland/pointer_interface.cpp b/src/wayland/pointer_interface.cpp
index a5549b5148..f9197fadd3 100644
--- a/src/wayland/pointer_interface.cpp
+++ b/src/wayland/pointer_interface.cpp
@@ -133,6 +133,12 @@ void PointerInterfacePrivate::sendFrame()
     }
 }
 
+bool PointerInterfacePrivate::AxisAccumulator::Axis::shouldReset(int newDirection) const
+{
+    // Reset the accumulator if the delta has opposite sign.
+    return direction && ((direction < 0) != (newDirection < 0));
+}
+
 PointerInterface::PointerInterface(SeatInterface *seat)
     : d(new PointerInterfacePrivate(this, seat))
 {
@@ -209,41 +215,28 @@ void PointerInterface::sendButton(quint32 button, PointerButtonState state, quin
     }
 }
 
-static bool shouldResetAccumulator(int accumulator, int delta)
-{
-    // Reset the accumulator if the delta has opposite sign.
-    return accumulator && (accumulator < 0 != delta < 0);
-}
-
 static void updateAccumulators(Qt::Orientation orientation, qreal delta, qint32 deltaV120, PointerInterfacePrivate *d, qint32 &valueAxisLowRes, qint32 &valueDiscrete)
 {
-    qint32 *accumulatorV120;
-    qreal *accumulatorAxis;
+    const int newDirection = deltaV120 > 0 ? 1 : -1;
+    auto &accum = d->axisAccumulator.axis(orientation);
 
-    if (orientation == Qt::Horizontal) {
-        accumulatorV120 = &d->accumulatorV120.rx();
-        accumulatorAxis = &d->accumulatorAxis.rx();
-    } else {
-        accumulatorV120 = &d->accumulatorV120.ry();
-        accumulatorAxis = &d->accumulatorAxis.ry();
+    if (accum.shouldReset(newDirection)) {
+        accum.reset();
     }
 
-    if (shouldResetAccumulator(*accumulatorV120, deltaV120)) {
-        *accumulatorV120 = 0;
-        *accumulatorAxis = 0;
-    }
+    accum.direction = newDirection;
 
-    *accumulatorAxis += delta;
-    *accumulatorV120 += deltaV120;
+    accum.axis += delta;
+    accum.axis120 += deltaV120;
 
     // ±120 is a "wheel click"
-    valueDiscrete = *accumulatorV120 / 120;
-    *accumulatorV120 -= valueDiscrete * 120;
+    valueDiscrete = accum.axis120 / 120;
+    accum.axis120 -= valueDiscrete * 120;
 
     if (valueDiscrete) {
         // Accumulate the axis values to send to low-res clients
-        valueAxisLowRes = *accumulatorAxis;
-        *accumulatorAxis = 0;
+        valueAxisLowRes = accum.axis;
+        accum.axis = 0;
     }
 }
 
diff --git a/src/wayland/pointer_interface_p.h b/src/wayland/pointer_interface_p.h
index c7783d3ce5..6a1d0921a9 100644
--- a/src/wayland/pointer_interface_p.h
+++ b/src/wayland/pointer_interface_p.h
@@ -25,6 +25,33 @@ class RelativePointerV1Interface;
 
 class PointerInterfacePrivate : public QtWaylandServer::wl_pointer
 {
+    struct AxisAccumulator
+    {
+        struct Axis
+        {
+            bool shouldReset(int newDirection) const;
+
+            void reset()
+            {
+                axis120 = 0;
+                axis = 0;
+            }
+
+            qint32 axis120 = 0;
+            qreal axis = 0;
+            int direction = 0;
+        };
+
+        Axis &axis(Qt::Orientation orientation)
+        {
+            const int index = orientation == Qt::Orientation::Horizontal ? 0 : 1;
+            return m_axis[index];
+        }
+
+    private:
+        Axis m_axis[2];
+    };
+
 public:
     static PointerInterfacePrivate *get(PointerInterface *pointer);
 
@@ -44,8 +71,7 @@ public:
     std::unique_ptr<PointerPinchGestureV1Interface> pinchGesturesV1;
     std::unique_ptr<PointerHoldGestureV1Interface> holdGesturesV1;
     QPointF lastPosition;
-    QPointF accumulatorAxis;
-    QPoint accumulatorV120;
+    AxisAccumulator axisAccumulator;
 
     void sendLeave(quint32 serial);
     void sendEnter(const QPointF &parentSurfacePosition, quint32 serial);