[PATCH] WheelHandler: smooth scroll for a greater variety of movement sizes

Duration is based on the duration and movement for 120 angle delta.
Shorten duration for smaller movements, limit duration for big movements.
We don't want fine deltas to feel extra slow and fast scrolling should still feel fast.
Minimum 3 frames for a 60hz display if delta > 2 physical pixels
(start already rendered -> 1/3 rendered -> 2/3 rendered -> end rendered).
Skip animation if <= 2 real frames for low refresh rate screens.
Otherwise, we don't scale the duration based on refresh rate or
device pixel ratio to avoid making the animation unexpectedly
longer or shorter on different screens.

BUG: 484309

Gbp-Pq: Name upstream_fb21ee82_WheelHandler-smooth-scroll-for-a-greater-variety-of-movement-sizes.patch

diff --git a/src/wheelhandler.cpp b/src/wheelhandler.cpp
index f8734a1211eb4958c885956f20a9ed28764d1da5..dc88b50de2a73e0079bf3ca2852b041e8dec334b 100644 (file)
--- a/src/wheelhandler.cpp
+++ b/src/wheelhandler.cpp
@@ -388,25 +388,12 @@ void WheelHandler::classBegin()
     m_engine = qmlEngine(this);
     m_units = m_engine->singletonInstance<Kirigami::Platform::Units *>("org.kde.kirigami.platform", "Units");
     m_settings = m_engine->singletonInstance<Kirigami::Platform::Settings *>("org.kde.kirigami.platform", "Settings");
-    initSmoothScrollDuration();
-
-    connect(m_units, &Kirigami::Platform::Units::longDurationChanged, this, &WheelHandler::initSmoothScrollDuration);
-    connect(m_settings, &Kirigami::Platform::Settings::smoothScrollChanged, this, &WheelHandler::initSmoothScrollDuration);
 }
 
 void WheelHandler::componentComplete()
 {
 }
 
-void WheelHandler::initSmoothScrollDuration()
-{
-    if (m_settings->smoothScroll()) {
-        m_yScrollAnimation.setDuration(m_units->longDuration());
-    } else {
-        m_yScrollAnimation.setDuration(0);
-    }
-}
-
 void WheelHandler::setScrolling(bool scrolling)
 {
     if (m_wheelScrolling == scrolling) {
@@ -514,11 +501,39 @@ bool WheelHandler::scrollFlickable(QPointF pixelDelta, QPointF angleDelta, Qt::K
         newContentY = std::round(newContentY * devicePixelRatio) / devicePixelRatio;
         if (contentY != newContentY) {
             scrolled = true;
-            if (m_wasTouched || !m_engine) {
-                m_flickable->setProperty("contentY", newContentY);
+            // Can't use wheelEvent->deviceType() to determine device type since
+            // on Wayland mouse is always regarded as touchpad:
+            // https://invent.kde.org/qt/qt/qtwayland/-/blob/e695a39519a7629c1549275a148cfb9ab99a07a9/src/client/qwaylandinputdevice.cpp#L445
+            // Mouse wheel can generate angle delta like 240, 360 and so on when
+            // scrolling very fast on some mice such as the Logitech M150.
+            // Mice with hi-res mouse wheels such as the Logitech MX Master 3 can
+            // generate angle deltas as small as 16.
+            // On X11, trackpads can also generate very fine angle deltas.
+            qreal refreshRate = window && window->screen() ? window->screen()->refreshRate() : 0;
+            if (m_settings->smoothScroll() && m_engine && refreshRate > 0) {
+                // Duration is based on the duration and movement for 120 angle delta.
+                // Shorten duration for smaller movements, limit duration for big movements.
+                // We don't want fine deltas to feel extra slow and fast scrolling should still feel fast.
+                // Minimum 3 frames for a 60hz display if delta > 2 physical pixels
+                // (start already rendered -> 1/3 rendered -> 2/3 rendered -> end rendered).
+                // Skip animation if <= 2 real frames for low refresh rate screens.
+                // Otherwise, we don't scale the duration based on refresh rate or
+                // device pixel ratio to avoid making the animation unexpectedly
+                // longer or shorter on different screens.
+                qreal absPixelDelta = std::abs(newContentY - contentY);
+                int duration = absPixelDelta * devicePixelRatio > 2 //
+                    ? std::clamp(qRound(absPixelDelta * m_units->longDuration() / m_verticalStepSize), qCeil(1000.0 / 60.0 * 3), m_units->longDuration())
+                    : 0;
+                m_yScrollAnimation.setDuration(duration <= qCeil(1000.0 / refreshRate * 2) ? 0 : duration);
+                if (m_yScrollAnimation.duration() > 0) {
+                    m_yScrollAnimation.setEndValue(newContentY);
+                    m_yScrollAnimation.start(QAbstractAnimation::KeepWhenStopped);
+                } else {
+                    m_flickable->setProperty("contentY", newContentY);
+                }
             } else {
-                m_yScrollAnimation.setEndValue(newContentY);
-                m_yScrollAnimation.start(QAbstractAnimation::KeepWhenStopped);
+                m_yScrollAnimation.setDuration(0);
+                m_flickable->setProperty("contentY", newContentY);
             }
         }
     }
@@ -602,13 +617,6 @@ bool WheelHandler::eventFilter(QObject *watched, QEvent *event)
         }
         QWheelEvent *wheelEvent = static_cast<QWheelEvent *>(event);
 
-        // Can't use wheelEvent->deviceType() to determine device type since on Wayland mouse is always regarded as touchpad
-        // https://invent.kde.org/qt/qt/qtwayland/-/blob/e695a39519a7629c1549275a148cfb9ab99a07a9/src/client/qwaylandinputdevice.cpp#L445
-        // and we can only expect a touchpad never generates the same angle delta as a mouse
-
-        // mouse wheel can also generate angle delta like 240, 360 and so on when scrolling very fast
-        // only checking wheelEvent->angleDelta().y() because we only animate for contentY
-        m_wasTouched = (std::abs(wheelEvent->angleDelta().y()) != 0 && std::abs(wheelEvent->angleDelta().y()) % 120 != 0);
         // NOTE: On X11 with libinput, pixelDelta is identical to angleDelta when using a mouse that shouldn't use pixelDelta.
         // If faulty pixelDelta, reset pixelDelta to (0,0).
         if (wheelEvent->pixelDelta() == wheelEvent->angleDelta()) {

diff --git a/src/wheelhandler.h b/src/wheelhandler.h
index 70ff9d9c782b9df4b6b71251e109f8051b9a738b..b1a4d269faae5c3061956fade0c557244ce7d2dd 100644 (file)
--- a/src/wheelhandler.h
+++ b/src/wheelhandler.h
@@ -361,7 +361,6 @@ private Q_SLOTS:
 private:
     void classBegin() override;
     void componentComplete() override;
-    void initSmoothScrollDuration();
 
     void setScrolling(bool scrolling);
     bool scrollFlickable(QPointF pixelDelta, QPointF angleDelta = {}, Qt::KeyboardModifiers modifiers = Qt::NoModifier);