feat: better notification storage and image caching + blobs

Plugins/ZShell/Components/CMakeLists.txt

@@ -14,6 +14,7 @@ qml_module(ZShell-components
 		roundedmask.hpp roundedmask.cpp
 		roundedclip.hpp roundedclip.cpp
 		snaplayout.hpp snaplayout.cpp
+		snapview.hpp snapview.cpp
 		wheelinverter.hpp
 	LIBRARIES
 		Qt::Quick

Plugins/ZShell/Components/snaplayout.cpp

@@ -17,6 +17,20 @@ qint64 originResidual(qreal logical, qreal dpr) {
 	return std::llround((device - std::floor(device)) * 1024.0) % 1024;
 }
 
+// Snap one size hint to the device grid. `mode` is >0 to round up, <0 to round
+// down, 0 to round to nearest. Infinities and NaN are left alone: they mean
+// "unbounded".
+qreal snapSizeHint(qreal value, qreal dpr, int mode) {
+	if (qIsNaN(value) || std::isinf(value)) return value;
+
+	const double exact = value * dpr;
+	const double snapped = mode > 0 ? std::ceil(exact - 1e-9)
+						   : mode < 0
+							   ? std::floor(exact + 1e-9)
+							   : static_cast<double>(std::llround(exact));
+	return snapped / dpr;
+}
+
 QPointF absoluteOrigin(const QQuickItem* item) {
 	qreal x = 0.0;
 	qreal y = 0.0;
@@ -102,9 +116,174 @@ void SnapLayout::itemChange(ItemChange change, const ItemChangeData& value) {
 	}
 }
 
+void SnapLayout::geometryChange(
+	const QRectF& newGeometry, const QRectF& oldGeometry) {
+	Q_D(SnapLayout);
+	QQuickLayout::geometryChange(newGeometry, oldGeometry);
+
+	if (!isReady()) return;
+
+	const QQuickWindow* win = window();
+	const qreal dpr = win ? win->effectiveDevicePixelRatio() : 0.0;
+	if (dpr <= 0.0) return;
+
+	// Any change of our own geometry can move us: our size changed and an anchor
+	// on a bottom or right edge moved us with it, or an ancestor resized and the
+	// same anchors moved us. Children were placed relative to the origin the
+	// arrangement saw: their local positions carry the compensation for that
+	// origin's fraction of a device pixel, so after a move they land on a
+	// fraction - which is why a centered child is blurred by a different amount
+	// every time the panel opens. Re-arrange whenever the origin's residual
+	// changes; it is remembered on every rearrange, so this fires only when a
+	// re-arrange is really needed, and it converges as soon as the animation
+	// stops moving the layout.
+	const QPointF origin = absoluteOrigin(this);
+	if (originResidual(origin.x(), dpr) == d->originResidualX &&
+		originResidual(origin.y(), dpr) == d->originResidualY)
+		return;
+
+	rearrangeForOriginMove();
+}
+
+// Children are placed against the origin the arrangement saw, so a move that
+// changes the origin's fraction of a device pixel needs a new arrangement.
+// polish() defers that to the next frame, and a polish request does nothing
+// while one is already pending - if no frame follows, or the pending polish is
+// never delivered, the children stay placed against the old origin forever.
+// Rearrange immediately instead; polish() is only the fallback for the cases
+// where rearranging now is not possible.
+void SnapLayout::rearrangeForOriginMove() {
+	Q_D(SnapLayout);
+	const QSizeF size(width(), height());
+	if (d->rearranging || size.width() <= 0.0 || size.height() <= 0.0) {
+		polish();
+		return;
+	}
+	rearrange(size);
+}
+
 QSizeF SnapLayout::sizeHint(Qt::SizeHint whichSizeHint) const {
 	Q_D(const SnapLayout);
-	return d->engine.sizeHint(whichSizeHint, QSizeF(), d->styleInfo);
+	const QSizeF engineHint =
+		d->engine.sizeHint(whichSizeHint, QSizeF(), d->styleInfo);
+
+	const QQuickWindow* win = window();
+	const qreal dpr = win ? win->effectiveDevicePixelRatio() : 1.0;
+	if (dpr <= 0.0) return engineHint;
+
+	const bool horiz = d->orientation == Qt::Horizontal;
+
+	// Qt builds implicit sizes out of whole logical pixels:
+	// QQuickLayout::effectiveSizeHints_helper takes `qCeil(item->implicitHeight())`
+	// for every child, so the sum can be an odd number of logical pixels, which is
+	// a half device pixel at a fractional ratio - 37 logical pixels at 1.5x is 55.5
+	// device pixels. A layout that sizes itself from its implicit size then has an
+	// edge on a fraction of a device pixel, and anchored to a bottom edge its top
+	// edge - and every child measured down from that top - lands off the grid.
+	//
+	// The preferred size is therefore summed here in device pixels: each child's
+	// own hint rounded up to the device grid, plus its Layout margins and the
+	// device-normalized spacing. That is exactly what the arrangement writes, so
+	// the layout is neither larger than its children (dead space, and a Flickable
+	// that reports more content height than the content occupies) nor smaller
+	// (the last child cut off).
+	qint64 mainExtentDev = 0;
+	qint64 crossDev = 0;
+	qint64 maxMainDev = 0;
+	int count = 0;
+
+	for (int i = 0; i < d->engine.itemCount(); ++i) {
+		const SnapGridLayoutItem* gridItem =
+			static_cast<const SnapGridLayoutItem*>(d->engine.itemAt(i));
+		QQuickItem* child = gridItem->layoutItem();
+		if (!child || shouldIgnoreItem(child)) continue;
+
+		QQuickLayoutAttached* info = attachedLayoutObject(child, false);
+		const QMarginsF margins = info ? info->effectiveQMargins()
+									   : QMarginsF(0, 0, 0, 0);
+
+		// The engine's per-child hints are authoritative: they follow
+		// Layout.preferredWidth/Height when those are set, otherwise the child's
+		// implicit size, otherwise the first width and height it had, and they
+		// include the child's Layout margins. They are also cached, so a nested
+		// layout contributes its own preferred size even before it is polished.
+		const QSizeF* hints = gridItem->effectiveSizeHints();
+
+		const qreal mainMargin = horiz ? margins.left() + margins.right()
+									   : margins.top() + margins.bottom();
+		const qreal crossMargin = horiz ? margins.top() + margins.bottom()
+										: margins.left() + margins.right();
+
+		qreal mainHint = (horiz ? hints[Qt::PreferredSize].width()
+								: hints[Qt::PreferredSize].height()) -
+						 mainMargin;
+		qreal crossHint = (horiz ? hints[Qt::PreferredSize].height()
+								 : hints[Qt::PreferredSize].width()) -
+						  crossMargin;
+
+		// The engine hint is `qCeil` of the implicit size, so it can sit up to a
+		// whole logical pixel above it - a device pixel per child at 1.5x, which
+		// adds up to dead space in a long column. When the child's own implicit
+		// size is known and the hint is just that ceiling, measure the implicit
+		// size and let the device rounding be the only rounding.
+		const qreal ownMain = horiz ? child->implicitWidth()
+									: child->implicitHeight();
+		if (ownMain > 0.0 && mainHint <= ownMain + 1.0) mainHint = ownMain;
+
+		const qreal ownCross = horiz ? child->implicitHeight()
+									 : child->implicitWidth();
+		if (ownCross > 0.0 && crossHint <= ownCross + 1.0) crossHint = ownCross;
+
+		if (!std::isfinite(mainHint) || mainHint < 0.0) mainHint = 0.0;
+		if (!std::isfinite(crossHint) || crossHint < 0.0) crossHint = 0.0;
+
+		// Rounding up keeps the hint from ever under-sizing its contents.
+		const qint64 mainDev = qint64(std::ceil(mainHint * dpr - 1e-9));
+		const qint64 mainMarginDev = qint64(std::ceil(mainMargin * dpr - 1e-9));
+		const qint64 crossDevForChild =
+			qint64(std::ceil(crossHint * dpr - 1e-9)) +
+			qint64(std::ceil(crossMargin * dpr - 1e-9));
+
+		mainExtentDev += mainDev + mainMarginDev;
+		maxMainDev = (std::max)(maxMainDev, mainDev + mainMarginDev);
+		crossDev = (std::max)(crossDev, crossDevForChild);
+		++count;
+	}
+
+	qreal space = d->spacingRequest;
+	if (qIsNaN(space)) space = d->styleInfo->spacing(d->orientation);
+	const qint64 gapDev = dpr > 0.0 ? qint64(std::llround(space * dpr))
+									: qint64(space);
+
+	if (uniformCellSizes() && count > 0)
+		mainExtentDev = maxMainDev * qint64(count);
+	if (count > 1) mainExtentDev += gapDev * qint64(count - 1);
+
+	const QSizeF preferred(
+		horiz ? qreal(mainExtentDev) / dpr : qreal(crossDev) / dpr,
+		horiz ? qreal(crossDev) / dpr : qreal(mainExtentDev) / dpr);
+
+	if (whichSizeHint == Qt::PreferredSize) return preferred;
+
+	if (whichSizeHint == Qt::MinimumSize) {
+		// Minimums round up, but never past the preferred size, or cells would
+		// grow past what the arrangement writes.
+		const QSizeF minimum(
+			snapSizeHint(engineHint.width(), dpr, 1),
+			snapSizeHint(engineHint.height(), dpr, 1));
+		return QSizeF(
+			(std::min)(minimum.width(), preferred.width()),
+			(std::min)(minimum.height(), preferred.height()));
+	}
+
+	// Maximums round down, but never below the preferred size: a layout is always
+	// allowed to be as large as its contents need.
+	const QSizeF maximum(
+		snapSizeHint(engineHint.width(), dpr, -1),
+		snapSizeHint(engineHint.height(), dpr, -1));
+	return QSizeF(
+		(std::max)(maximum.width(), preferred.width()),
+		(std::max)(maximum.height(), preferred.height()));
 }
 
 Qt::Orientation SnapLayout::orientation() const {
@@ -325,24 +504,33 @@ void SnapLayout::itemVisibilityChanged(QQuickItem* item) {
 
 void SnapLayout::itemGeometryChanged(
 	QQuickItem* item, QQuickGeometryChange change, const QRectF& oldGeometry) {
-	Q_UNUSED(item);
-	Q_UNUSED(oldGeometry);
-	if (!isReady() || !change.positionChange()) return;
+	Q_UNUSED(item)
+	Q_UNUSED(change)
+	Q_UNUSED(oldGeometry)
+	if (!isReady()) return;
 
-	Q_D(SnapLayout);
 	const QQuickWindow* win = window();
 	const qreal dpr = win ? win->effectiveDevicePixelRatio() : 0.0;
 	if (dpr <= 0.0) return;
 
+	// An ancestor changing size can move us too - a layout anchored to a bottom
+	// edge slides when its parent grows - so only the origin's fraction of a
+	// device pixel matters, not which kind of change reached us.
+	Q_D(SnapLayout);
 	const QPointF origin = absoluteOrigin(this);
 	if (originResidual(origin.x(), dpr) == d->originResidualX &&
 		originResidual(origin.y(), dpr) == d->originResidualY)
 		return;
-	polish();
+
+	rearrangeForOriginMove();
 }
 
 void SnapLayout::updateAncestorListeners() {
 	Q_D(SnapLayout);
+
+	const QFlags<QQuickItemPrivate::ChangeType> mask =
+		QQuickItemPrivate::Geometry;
+
 	QVector<QQuickItem*> current;
 	for (QQuickItem* it = parentItem(); it; it = it->parentItem()) {
 		if (qobject_cast<SnapLayout*>(it)) break;
@@ -351,15 +539,34 @@ void SnapLayout::updateAncestorListeners() {
 
 	for (const QPointer<QQuickItem>& ancestor :
 		 std::as_const(d->ancestorListeners)) {
-		if (ancestor && !current.contains(ancestor.data()))
+		if (ancestor && !current.contains(ancestor.data())) {
 			QQuickItemPrivate::get(ancestor.data())
-				->removeItemChangeListener(this, QQuickItemPrivate::Geometry);
+				->removeItemChangeListener(
+					this, d->ancestorMasks.value(ancestor.data()));
+			d->ancestorMasks.remove(ancestor.data());
+		}
 	}
+
+	// Qt appends one registration per addItemChangeListener call, so only the
+	// bits that are not registered yet may be added; re-adding the same mask on
+	// every rearrange would duplicate listeners without bound.
 	for (QQuickItem* ancestor : std::as_const(current)) {
-		if (!d->ancestorListeners.contains(ancestor))
+		const auto have = d->ancestorMasks.value(ancestor);
+		const auto missing = mask & ~have;
+		const auto extra = have & ~mask;
+
+		if (extra != 0) {
+			QQuickItemPrivate::get(ancestor)->removeItemChangeListener(
+				this, extra);
+		}
+		if (missing != 0) {
 			QQuickItemPrivate::get(ancestor)->addItemChangeListener(
-				this, QQuickItemPrivate::Geometry);
+				this, missing);
+		}
+
+		d->ancestorMasks[ancestor] = mask;
 	}
+
 	d->ancestorListeners.clear();
 	d->ancestorListeners.reserve(current.size());
 	for (QQuickItem* ancestor : std::as_const(current))
@@ -370,10 +577,13 @@ void SnapLayout::clearAncestorListeners() {
 	Q_D(SnapLayout);
 	for (const QPointer<QQuickItem>& ancestor :
 		 std::as_const(d->ancestorListeners)) {
-		if (ancestor)
+		if (ancestor) {
 			QQuickItemPrivate::get(ancestor.data())
-				->removeItemChangeListener(this, QQuickItemPrivate::Geometry);
+				->removeItemChangeListener(
+					this, d->ancestorMasks.value(ancestor.data()));
+		}
 	}
+	d->ancestorMasks.clear();
 	d->ancestorListeners.clear();
 }
 
@@ -393,6 +603,13 @@ void SnapLayout::arrangeChildren() {
 	qint64 prevSizeDev = 0;
 	bool started = false;
 
+	// The layout's own main extent, rounded down: no child is placed past it, so
+	// a Flickable that takes this layout's height as its content height can still
+	// reach the last child.
+	const QSizeF self = size();
+	const qint64 layoutMainExtentDev =
+		qint64(std::floor((horiz ? self.width() : self.height()) * dpr + 1e-6));
+
 	for (int i = 0; i < d->engine.itemCount(); ++i) {
 		SnapGridLayoutItem* gridItem =
 			static_cast<SnapGridLayoutItem*>(d->engine.itemAt(i));
@@ -419,16 +636,83 @@ void SnapLayout::arrangeChildren() {
 					   std::llround(mainExact - prevEndExact);
 		}
 
-		const qint64 mainFarDev = std::llround(mainExact + mainSizeExact);
+		const qint64 mainFarExact = std::llround(mainExact + mainSizeExact);
+
+		// An aligned child whose cell is its own implicit size is sized from that
+		// implicit size. The engine recomputes cells from animated geometry, so a
+		// cell that is mathematically 41 can arrive as 40.9999999999; when the
+		// device pixel ratio puts 41 exactly on half a device pixel, that epsilon
+		// flips the rounding from pass to pass and the child visibly resizes while
+		// it only moves. Children that fill their axis, or whose cell has grown
+		// past their implicit size, keep the engine-derived size so that animated
+		// fills still step through device pixels.
+		QQuickLayoutAttached* info = attachedLayoutObject(child, false);
+		const qreal mainOwn = horiz ? child->implicitWidth()
+									: child->implicitHeight();
+		const qreal crossOwn = horiz ? child->implicitHeight()
+									 : child->implicitWidth();
+		const bool fillsMain = info &&
+							   (horiz ? info->fillWidth() : info->fillHeight());
+		const bool fillsCross =
+			info && (horiz ? info->fillHeight() : info->fillWidth());
+
+		const auto snappedOwn = [&](bool fills, qreal cellSize, qreal ownSize) {
+			if (fills || ownSize <= 0.0 || qAbs(cellSize - ownSize) >= 1.0)
+				return qint64(-1);
+			// Round up, like Qt's `qCeil` of implicit sizes: a child is never
+			// smaller than the content it holds, and this is the same rounding
+			// sizeHint() sums to compute the layout's own preferred size, so the
+			// children fill the layout without slack and without overflow.
+			return (std::max)(qint64(std::ceil(ownSize * dpr - 1e-9)),
+							  qint64(0));
+		};
+
+		const qint64 mainOwnDev =
+			snappedOwn(fillsMain, horiz ? cell.width() : cell.height(), mainOwn);
+		const qint64 crossOwnDev = snappedOwn(
+			fillsCross, horiz ? cell.height() : cell.width(), crossOwn);
+
+		// The size along the main axis. An implicit-sized child keeps its own
+		// implicit size, which carries the device-pixel parity ZUtils chose for
+		// it. Rounding is not neutral: an odd logical size at 1.5x is exactly half
+		// a device pixel and always rounds up, so left unchecked every child adds
+		// half a pixel and a long list ends outside the layout - a Flickable reads
+		// the layout's height as the end of the content and the last rows become
+		// unreachable. Corrections are made in steps of two device pixels: an item
+		// that centers its own content (Layout.HCenter / Layout.VCenter,
+		// anchors.centerIn) lands on whole device pixels only while its device
+		// size keeps that parity, so a one-pixel correction moves its centered
+		// children onto half a pixel and they antialias. Drift from the engine's
+		// edge is bounded at two device pixels, and no child is placed past the
+		// layout's own edge - a layout with less room than its children needs
+		// overflows in Qt too, so the engine's own edge is never pulled back.
+		const qint64 mainFarCeil =
+			(std::max)(mainFarExact, layoutMainExtentDev);
+		const qint64 mainLimit =
+			(std::min)(mainFarExact + 2, mainFarCeil) - mainNear;
 
-		const auto stored = d->childSizes.constFind(child);
 		qint64 width = engineWidth;
 		qint64 height = engineHeight;
+		const qint64 mainSizeWritten =
+			mainOwnDev >= 0 ? mainOwnDev
+							: (std::max)(mainFarExact - mainNear, qint64(0));
 		if (horiz)
-			width = std::max(mainFarDev - mainNear, qint64(0));
+			width = mainSizeWritten;
 		else
-			height = std::max(mainFarDev - mainNear, qint64(0));
+			height = mainSizeWritten;
 
+		if (crossOwnDev >= 0) {
+			if (horiz)
+				height = crossOwnDev;
+			else
+				width = crossOwnDev;
+		}
+
+		// Keep the size already written unless the engine asks for a different
+		// one, or something else resized the child. An aligned size stays
+		// aligned wherever the layout moves, and resizing again costs the child
+		// a relayout: an Image reloads its texture, a nested layout rearranges.
+		const auto stored = d->childSizes.constFind(child);
 		if (stored != d->childSizes.constEnd() &&
 			stored.value().engineWidth == engineWidth &&
 			stored.value().engineHeight == engineHeight &&
@@ -436,11 +720,22 @@ void SnapLayout::arrangeChildren() {
 			std::llround(child->height() * dpr) == stored.value().height) {
 			width = stored.value().width;
 			height = stored.value().height;
-		} else {
-			d->childSizes[child] = SnapLayoutPrivate::ChildSize{
-				engineWidth, engineHeight, width, height};
 		}
 
+		// A remembered size can predate the layout being sized, so the limit is
+		// applied to whatever ends up being written, keeping the parity of the
+		// size this child is asking for.
+		qint64& mainAxisSize = horiz ? width : height;
+		const int mainParity = int(mainAxisSize % 2);
+		if (mainAxisSize > mainLimit) {
+			mainAxisSize = mainLimit;
+			if (int(mainAxisSize % 2) != mainParity) --mainAxisSize;
+		}
+		mainAxisSize = (std::max)(mainAxisSize, qint64(0));
+
+		d->childSizes[child] = SnapLayoutPrivate::ChildSize{
+			engineWidth, engineHeight, width, height};
+
 		prevEndExact = mainExact + mainSizeExact;
 		prevNearDev = mainNear;
 		prevSizeDev = horiz ? width : height;

Plugins/ZShell/Components/snaplayout.hpp

@@ -84,6 +84,9 @@ class SnapLayout : public QQuickLayout {
 
 	void itemChange(ItemChange change, const ItemChangeData& value) override;
 
+	void geometryChange(
+		const QRectF& newGeometry, const QRectF& oldGeometry) override;
+
 	void itemDestroyed(QQuickItem* item) override;
 	void itemVisibilityChanged(QQuickItem* item) override;
 	void itemGeometryChanged(
@@ -118,6 +121,9 @@ class SnapLayout : public QQuickLayout {
 
 	void arrangeChildren();
 
+	// Re-arranges when the origin moved by a fraction of a device pixel.
+	void rearrangeForOriginMove();
+
 	void applySpacing();
 
 	void updateAncestorListeners();
@@ -142,6 +148,7 @@ class SnapLayoutPrivate : public QQuickLayoutPrivate {
 	QList<QQuickItem*> invalidateAfterRearrange;
 
 	QVector<QPointer<QQuickItem>> ancestorListeners;
+	QHash<QQuickItem*, QFlags<QQuickItemPrivate::ChangeType>> ancestorMasks;
 	qint64 originResidualX = -1;
 	qint64 originResidualY = -1;
 

Plugins/ZShell/Components/snapview.cpp

@@ -0,0 +1,806 @@
+#include "snapview.hpp"
+
+#include <QQuickWindow>
+#include <QTimer>
+#include <private/qquickflickable_p.h>
+#include <private/qquickflickable_p_p.h>
+#include <algorithm>
+#include <cmath>
+#include <limits>
+
+namespace ZShell::components {
+namespace {
+
+// The same device-pixel helpers SnapLayout uses: the residual is the fractional
+// part of an absolute device-pixel position, which is how a sub-pixel move of
+// the view or its ancestors is noticed without reacting to whole-pixel moves.
+qint64 originResidual(qreal logical, qreal dpr) {
+	const qreal device = logical * dpr;
+	return std::llround((device - std::floor(device)) * 1024.0) % 1024;
+}
+
+QPointF absoluteOrigin(const QQuickItem* item) {
+	qreal x = 0.0;
+	qreal y = 0.0;
+	for (const QQuickItem* it = item; it; it = it->parentItem()) {
+		x += it->x();
+		y += it->y();
+	}
+	return QPointF(x, y);
+}
+
+constexpr int AsyncBatchSize = 4;
+
+// Sizes are compared with a tolerance rather than ==, because the snapped
+// logical values are quotients of device pixels and never exact.
+bool differs(qreal a, qreal b) {
+	return qAbs(a - b) > 0.001;
+}
+
+// Geometry is watched to notice sub-pixel moves; Destroyed is watched so a
+// listener can be dropped while the item is still valid instead of at teardown.
+constexpr QFlags<QQuickItemPrivate::ChangeType> WatchedChanges =
+	QQuickItemPrivate::Geometry | QQuickItemPrivate::Destroyed;
+
+void addGeometryListener(QQuickItem* item, QQuickItemChangeListener* listener) {
+	if (item)
+		QQuickItemPrivate::get(item)->addItemChangeListener(
+			listener, WatchedChanges);
+}
+
+void removeGeometryListener(
+	QQuickItem* item, QQuickItemChangeListener* listener) {
+	if (item)
+		QQuickItemPrivate::get(item)->removeItemChangeListener(
+			listener, WatchedChanges);
+}
+
+} // namespace
+
+SnapView::SnapView(QQuickItem* parent) : QQuickFlickable(parent) {
+	setClip(true);
+
+	// Asynchronous batches are spread over event loop turns, so the frames
+	// between them can render; polish() from updatePolish would run them all
+	// inside one polish flush.
+	m_asyncTimer = new QTimer(this);
+	m_asyncTimer->setSingleShot(true);
+	m_asyncTimer->setInterval(0);
+	connect(m_asyncTimer, &QTimer::timeout, this, &SnapView::polish);
+}
+
+SnapView::~SnapView() {
+	clearListeners();
+	disconnectModel();
+}
+
+QAbstractItemModel* SnapView::model() const {
+	return m_model.data();
+}
+
+void SnapView::setModel(QAbstractItemModel* model) {
+	if (m_model == model) return;
+
+	disconnectModel();
+	for (int index : m_items.keys())
+		destroyDelegate(index);
+	m_sizeDevCache.clear();
+	m_rowSizes.clear();
+
+	m_model = model;
+	invalidateRoleNames();
+	connectModel();
+	rebuildRows();
+
+	if (m_componentComplete) polish();
+	emit modelChanged();
+}
+
+QQmlComponent* SnapView::delegate() const {
+	return m_delegate.data();
+}
+
+void SnapView::setDelegate(QQmlComponent* delegate) {
+	if (m_delegate == delegate) return;
+
+	m_delegate = delegate;
+	for (int index : m_items.keys())
+		destroyDelegate(index);
+	m_pendingCreate.clear();
+	m_sizeDevCache.clear();
+
+	if (m_componentComplete) polish();
+	emit delegateChanged();
+}
+
+Qt::Orientation SnapView::orientation() const {
+	return m_orientation;
+}
+
+void SnapView::setOrientation(Qt::Orientation orientation) {
+	if (m_orientation == orientation) return;
+	m_orientation = orientation;
+	invalidateMainAxisCaches();
+	if (m_componentComplete) polish();
+	emit orientationChanged();
+}
+
+qreal SnapView::spacing() const {
+	return m_spacing;
+}
+
+void SnapView::setSpacing(qreal spacing) {
+	if (qFuzzyCompare(m_spacing, spacing)) return;
+	m_spacing = spacing;
+	if (m_componentComplete) polish();
+	emit spacingChanged();
+}
+
+qreal SnapView::cacheBuffer() const {
+	return m_cacheBuffer;
+}
+
+void SnapView::setCacheBuffer(qreal buffer) {
+	if (qFuzzyCompare(m_cacheBuffer, buffer)) return;
+	m_cacheBuffer = buffer;
+	if (m_componentComplete) polish();
+	emit cacheBufferChanged();
+}
+
+qreal SnapView::estimatedSize() const {
+	return m_estimatedSize;
+}
+
+void SnapView::setEstimatedSize(qreal size) {
+	if (qFuzzyCompare(m_estimatedSize, size)) return;
+	m_estimatedSize = size;
+	if (m_componentComplete) polish();
+	emit estimatedSizeChanged();
+}
+
+bool SnapView::snapSizes() const {
+	return m_snapSizes;
+}
+
+void SnapView::setSnapSizes(bool snapSizes) {
+	if (m_snapSizes == snapSizes) return;
+	m_snapSizes = snapSizes;
+	if (m_componentComplete) polish();
+	emit snapSizesChanged();
+}
+
+bool SnapView::asynchronous() const {
+	return m_asynchronous;
+}
+
+void SnapView::setAsynchronous(bool asynchronous) {
+	if (m_asynchronous == asynchronous) return;
+	m_asynchronous = asynchronous;
+	if (m_componentComplete) polish();
+	emit asynchronousChanged();
+}
+
+int SnapView::count() const {
+	return m_model ? m_model->rowCount() : 0;
+}
+
+int SnapView::currentIndex() const {
+	return m_currentIndex;
+}
+
+void SnapView::setCurrentIndex(int index) {
+	if (m_currentIndex == index) return;
+	m_currentIndex = index;
+	emit currentIndexChanged();
+	emit currentItemChanged();
+}
+
+QQuickItem* SnapView::currentItem() const {
+	return m_items.value(m_currentIndex, nullptr);
+}
+
+void SnapView::positionViewAtBeginning() {
+	positionViewAtIndex(0);
+}
+
+void SnapView::positionViewAtEnd() {
+	positionViewAtIndex(count() - 1);
+}
+
+void SnapView::positionViewAtIndex(int index) {
+	if (!m_componentComplete || index < 0 || index >= m_rows.size()) return;
+
+	// Summed here rather than read from m_rows, whose offsets only refresh on
+	// polish: positioning must be right even when called between passes.
+	const bool horiz = m_orientation == Qt::Horizontal;
+	const qreal extent = horiz ? width() : height();
+	const qreal spacing = effectiveSpacing();
+
+	qreal offset = 0.0;
+	qreal target = 0.0;
+	qreal total = 0.0;
+	for (int i = 0; i < m_rows.size(); ++i) {
+		if (i == index) target = offset;
+		const qreal size = rowSize(i);
+		total = offset + size;
+		offset += size + spacing;
+	}
+
+	const qreal position =
+		std::clamp(target, 0.0, (std::max)(0.0, total - extent));
+	const qint64 positionDev = std::llround(position * devicePixelRatio());
+	const qreal snapped = qreal(positionDev) / devicePixelRatio();
+	if (horiz)
+		setContentX(snapped);
+	else
+		setContentY(snapped);
+}
+
+qreal SnapView::devicePixelRatio() const {
+	const QQuickWindow* win = window();
+	const qreal dpr = win ? win->effectiveDevicePixelRatio() : 1.0;
+	return dpr > 0.0 ? dpr : 1.0;
+}
+
+void SnapView::componentComplete() {
+	QQuickFlickable::componentComplete();
+	m_componentComplete = true;
+	rebuildRows();
+	updateAncestorListeners();
+	polish();
+}
+
+void SnapView::geometryChange(
+	const QRectF& newGeometry, const QRectF& oldGeometry) {
+	QQuickFlickable::geometryChange(newGeometry, oldGeometry);
+	if (m_componentComplete && !m_placing &&
+		newGeometry.size() != oldGeometry.size()) {
+		polish();
+	}
+}
+
+void SnapView::itemChange(ItemChange change, const ItemChangeData& value) {
+	QQuickFlickable::itemChange(change, value);
+	if (change == ItemSceneChange) {
+		// Leaving the scene means the ancestors are going away: drop the
+		// listeners now, while both sides are still whole.
+		if (value.window) {
+			updateAncestorListeners();
+			polish();
+		} else {
+			clearListeners();
+		}
+		return;
+	}
+	if (change == ItemDevicePixelRatioHasChanged) {
+		updateAncestorListeners();
+		polish();
+	}
+}
+
+void SnapView::updatePolish() {
+	if (!m_componentComplete) return;
+	layoutAndPlace();
+	if (!m_pendingCreate.isEmpty() && m_asynchronous) m_asyncTimer->start();
+}
+
+void SnapView::itemGeometryChanged(
+	QQuickItem* item, QQuickGeometryChange change, const QRectF& oldGeometry) {
+	Q_UNUSED(oldGeometry)
+	if (!m_componentComplete || m_placing) return;
+
+	const qreal dpr = devicePixelRatio();
+
+	QQuickItem* content = QQuickFlickablePrivate::get(this)->contentItem;
+	const bool watched = std::any_of(
+		m_ancestorListeners.constBegin(),
+		m_ancestorListeners.constEnd(),
+		[item](const QPointer<QQuickItem>& p) { return p == item; });
+	if (item == content || watched) {
+		const QPointF origin = contentOrigin();
+		if (originResidual(origin.x(), dpr) != m_originResidualX ||
+			originResidual(origin.y(), dpr) != m_originResidualY) {
+			polish();
+		}
+		return;
+	}
+
+	if (change.sizeChange() && m_items.key(item, -1) >= 0) polish();
+}
+
+void SnapView::itemDestroyed(QQuickItem* item) {
+	m_sizeDevCache.remove(item);
+	const auto isItem = [item](const QPointer<QQuickItem>& p) {
+		return p == item;
+	};
+	m_delegateListeners.erase(
+		std::remove_if(
+			m_delegateListeners.begin(), m_delegateListeners.end(), isItem),
+		m_delegateListeners.end());
+	m_ancestorListeners.erase(
+		std::remove_if(
+			m_ancestorListeners.begin(), m_ancestorListeners.end(), isItem),
+		m_ancestorListeners.end());
+	const int index = m_items.key(item, -1);
+	if (index >= 0) {
+		m_items.remove(index);
+		emit currentItemChanged();
+	}
+}
+
+qreal SnapView::effectiveSpacing() const {
+	return qreal(std::llround(m_spacing * devicePixelRatio())) /
+		   devicePixelRatio();
+}
+
+qreal SnapView::rowSize(int index) const {
+	QQuickItem* item = m_items.value(index, nullptr);
+	if (item) {
+		const qreal measured = m_orientation == Qt::Horizontal ? item->width()
+															   : item->height();
+		if (measured > 0.0) return measured;
+	}
+
+	const qreal cached = m_rowSizes.value(index, 0.0);
+	if (cached > 0.0) return cached;
+	return m_estimatedSize > 0.0 ? m_estimatedSize : 0.0;
+}
+
+qint64 SnapView::snappedDeviceMainSize(QQuickItem* item) {
+	const qreal dpr = devicePixelRatio();
+
+	const qreal own = m_orientation == Qt::Horizontal ? item->width()
+													  : item->height();
+	if (own <= 0.0) return 0;
+
+	// Reuse the cached device size while the item's own size is still within a
+	// device pixel of it, so an item that only moves keeps its size.
+	const qint64 cached = m_sizeDevCache.value(item, -1);
+	if (cached >= 0 && qAbs(own * dpr - qreal(cached)) <= 1.0) return cached;
+
+	const qint64 snapped = std::llround(own * dpr);
+	m_sizeDevCache[item] = snapped;
+	return snapped;
+}
+
+int SnapView::firstVisibleIndex() const {
+	if (m_rows.isEmpty()) return 0;
+
+	// Row ends are non-decreasing (offsets accumulate size plus spacing), so the
+	// visible range can be found by binary search instead of a linear scan.
+	const qreal start = m_orientation == Qt::Horizontal ? contentX()
+														: contentY();
+	const qreal from = (std::max)(0.0, start - m_cacheBuffer);
+
+	const auto it = std::lower_bound(
+		m_rows.constBegin(),
+		m_rows.constEnd(),
+		from,
+		[](const Row& row, qreal value) {
+			return row.exactOffset + row.exactSize < value;
+		});
+	return static_cast<int>(std::distance(m_rows.constBegin(), it));
+}
+
+int SnapView::lastVisibleIndex() const {
+	if (m_rows.isEmpty()) return 0;
+
+	const bool horiz = m_orientation == Qt::Horizontal;
+	const qreal start = horiz ? contentX() : contentY();
+	const qreal extent = horiz ? width() : height();
+	const qreal to = start + extent + m_cacheBuffer;
+
+	const auto it = std::lower_bound(
+		m_rows.constBegin(),
+		m_rows.constEnd(),
+		to,
+		[](const Row& row, qreal value) { return row.exactOffset <= value; });
+	if (it == m_rows.constBegin()) return 0;
+	return static_cast<int>(std::distance(m_rows.constBegin(), it)) - 1;
+}
+
+QPointF SnapView::contentOrigin() const {
+	// QQuickFlickablePrivate::get has no const overload; the item private is the
+	// base of the flickable private, so casting is the const path to it.
+	const auto* priv = static_cast<const QQuickFlickablePrivate*>(
+		QQuickItemPrivate::get(this));
+	return absoluteOrigin(priv->contentItem);
+}
+
+void SnapView::layoutAndPlace() {
+	const qreal dpr = devicePixelRatio();
+
+	const bool horiz = m_orientation == Qt::Horizontal;
+	const qreal spacing = effectiveSpacing();
+
+	// Cumulative exact offsets, so the rounding below has the same exact
+	// reference SnapLayout's arrangeChildren works from. Running this before
+	// updateDelegates gives the viewport range to recycle against, and running
+	// it again afterwards picks up sizes that changed when a re-keyed delegate
+	// got a new index.
+	const auto accumulate = [&]() {
+		qreal offset = 0.0;
+		for (int i = 0; i < m_rows.size(); ++i) {
+			qreal size = rowSize(i);
+			QQuickItem* item = m_items.value(i, nullptr);
+			if (item) {
+				const qreal measured = horiz ? item->width() : item->height();
+				if (measured > 0.0) m_rowSizes[i] = measured;
+			}
+
+			m_rows[i].exactOffset = offset;
+			m_rows[i].exactSize = size;
+			offset += size + spacing;
+		}
+		return m_rows.isEmpty() ? 0.0 : offset - spacing;
+	};
+
+	accumulate();
+	updateDelegates();
+	const qreal total = accumulate();
+
+	if (horiz)
+		setContentWidth(qreal(std::llround(total * dpr)) / dpr);
+	else
+		setContentHeight(qreal(std::llround(total * dpr)) / dpr);
+
+	QQuickItem* content = QQuickFlickablePrivate::get(this)->contentItem;
+	if (!content) return;
+
+	const QPointF origin = absoluteOrigin(content);
+	const qint64 originXDev = std::llround(origin.x() * dpr);
+	const qint64 originYDev = std::llround(origin.y() * dpr);
+	const qint64 crossDev = std::llround((horiz ? height() : width()) * dpr);
+
+	qint64 prevNear = 0;
+	qint64 prevSizeDev = 0;
+	qreal prevEndExact = 0.0;
+	bool started = false;
+
+	m_placing = true;
+	for (int i = 0; i < m_rows.size(); ++i) {
+		const Row& row = m_rows.at(i);
+		const qreal mainExact = row.exactOffset * dpr;
+
+		qint64 mainNear = 0;
+		if (!started) {
+			mainNear = std::llround(mainExact);
+			started = true;
+		} else {
+			mainNear =
+				prevNear + prevSizeDev + std::llround(mainExact - prevEndExact);
+		}
+
+		QQuickItem* item = m_items.value(i, nullptr);
+		qint64 mainDev = std::llround(row.exactSize * dpr);
+		if (item) {
+			const qint64 ownDev = snappedDeviceMainSize(item);
+			if (ownDev > 0) mainDev = ownDev;
+		}
+
+		prevEndExact = mainExact + row.exactSize * dpr;
+		prevSizeDev = mainDev;
+		prevNear = mainNear;
+
+		if (!item) continue;
+
+		const qreal mainSize = qreal(mainDev) / dpr;
+		const qreal crossSize = qreal(crossDev) / dpr;
+
+		const qreal posX = horiz
+							   ? qreal(originXDev + mainNear) / dpr - origin.x()
+							   : qreal(originXDev) / dpr - origin.x();
+		const qreal posY =
+			horiz ? qreal(originYDev) / dpr - origin.y()
+				  : qreal(originYDev + mainNear) / dpr - origin.y();
+		item->setPosition(QPointF(posX, posY));
+
+		// Only the cross axis is written unconditionally. Writing the main axis
+		// would replace the delegate's implicit-size fallback with an explicit
+		// value, so a delegate whose content changes size could never grow
+		// again. It is resized only when snapSizes asks for exactly that.
+		if (horiz) {
+			if (m_snapSizes && mainDev > 0 && differs(item->width(), mainSize))
+				item->setWidth(mainSize);
+			if (differs(item->height(), crossSize)) item->setHeight(crossSize);
+		} else {
+			if (differs(item->width(), crossSize)) item->setWidth(crossSize);
+			if (m_snapSizes && mainDev > 0 && differs(item->height(), mainSize))
+				item->setHeight(mainSize);
+		}
+	}
+	m_placing = false;
+
+	trackOriginResidual();
+}
+
+void SnapView::updateDelegates() {
+	const int first = firstVisibleIndex();
+	const int last = lastVisibleIndex();
+
+	for (int index : m_items.keys()) {
+		if (index < first || index > last) destroyDelegate(index);
+	}
+
+	QVector<int> missing;
+	for (int index = first; index <= last; ++index) {
+		if (m_items.contains(index))
+			updateDelegateData(index);
+		else
+			missing.append(index);
+	}
+
+	int budget = m_asynchronous ? AsyncBatchSize
+								: (std::numeric_limits<int>::max)();
+	m_pendingCreate.clear();
+	for (int index : std::as_const(missing)) {
+		if (budget <= 0) {
+			m_pendingCreate.append(index);
+			continue;
+		}
+		(void)createDelegate(index);
+		--budget;
+	}
+}
+
+QQuickItem* SnapView::createDelegate(int index) {
+	if (!m_delegate || !m_model || index < 0 || index >= m_model->rowCount())
+		return nullptr;
+	if (m_items.contains(index)) return m_items.value(index);
+
+	// Same as LazyListView: beginCreate + setInitialProperties + completeCreate,
+	// so delegates with pragma ComponentBehavior: Bound are accepted.
+	auto* compContext = m_delegate->creationContext();
+	if (!compContext) compContext = qmlContext(this);
+	if (!compContext) return nullptr;
+
+	QObject* obj = m_delegate->beginCreate(compContext);
+	QQuickItem* item = qobject_cast<QQuickItem*>(obj);
+	if (!item) {
+		qWarning(
+			"SnapView: delegate creation failed for row %d: %s",
+			index,
+			qPrintable(m_delegate->errorString()));
+		if (obj) m_delegate->completeCreate();
+		delete obj;
+		return nullptr;
+	}
+
+	m_delegate->setInitialProperties(item, delegateProperties(index));
+
+	QQuickItem* content = QQuickFlickablePrivate::get(this)->contentItem;
+	item->setParentItem(content ? content : this);
+	addGeometryListener(item, this);
+	m_delegateListeners.append(item);
+	m_items.insert(index, item);
+
+	m_delegate->completeCreate();
+
+	emit currentItemChanged();
+	return item;
+}
+
+void SnapView::destroyDelegate(int index) {
+	QQuickItem* item = m_items.take(index);
+	if (!item) return;
+
+	removeGeometryListener(item, this);
+	m_delegateListeners.removeAll(item);
+	m_sizeDevCache.remove(item);
+	item->deleteLater();
+	emit currentItemChanged();
+}
+
+void SnapView::updateDelegateData(int index) {
+	QQuickItem* item = m_items.value(index, nullptr);
+	if (!item) return;
+
+	const QVariantMap props = delegateProperties(index);
+	for (auto it = props.constBegin(); it != props.constEnd(); ++it) {
+		const QByteArray name = it.key().toUtf8();
+		// Scrolls refresh every visible delegate each pass; writing only the
+		// values that actually changed keeps that cheap.
+		if (item->property(name.constData()) == it.value()) continue;
+		item->setProperty(name.constData(), it.value());
+	}
+}
+
+QVariantMap SnapView::delegateProperties(int index) {
+	QVariantMap props;
+	if (!m_model || index < 0 || index >= m_model->rowCount()) return props;
+
+	const QModelIndex srcIndex = m_model->index(index, 0);
+	const auto& names = roleNames();
+	bool hasModelData = false;
+
+	for (auto it = names.constBegin(); it != names.constEnd(); ++it) {
+		const auto name = QString::fromUtf8(it.value());
+		props.insert(name, m_model->data(srcIndex, it.key()));
+		if (name == QStringLiteral("modelData")) hasModelData = true;
+	}
+
+	props.insert(QStringLiteral("index"), index);
+
+	if (!hasModelData) {
+		const auto role = names.isEmpty() ? Qt::DisplayRole
+										  : names.constBegin().key();
+		props.insert(QStringLiteral("modelData"), m_model->data(srcIndex, role));
+	}
+
+	return props;
+}
+
+const QHash<int, QByteArray>& SnapView::roleNames() {
+	if (!m_roleNamesValid) {
+		m_roleNames = m_model ? m_model->roleNames() : QHash<int, QByteArray>();
+		m_roleNamesValid = true;
+	}
+	return m_roleNames;
+}
+
+void SnapView::invalidateRoleNames() {
+	m_roleNamesValid = false;
+}
+
+void SnapView::invalidateMainAxisCaches() {
+	// Cached sizes belong to the axis that is no longer the main one.
+	m_rowSizes.fill(0.0);
+	m_sizeDevCache.clear();
+}
+
+void SnapView::rebuildRows() {
+	m_rows.resize(count());
+	m_rowSizes.resize(count());
+	if (m_currentIndex >= count()) m_currentIndex = -1;
+	emit countChanged();
+	emit currentItemChanged();
+}
+
+void SnapView::trackOriginResidual() {
+	const qreal dpr = devicePixelRatio();
+	const QPointF origin = contentOrigin();
+	m_originResidualX = originResidual(origin.x(), dpr);
+	m_originResidualY = originResidual(origin.y(), dpr);
+}
+
+void SnapView::shiftDelegateIndices(int from, int delta) {
+	if (delta == 0) return;
+
+	QHash<int, QQuickItem*> shifted;
+	for (auto it = m_items.constBegin(); it != m_items.constEnd(); ++it) {
+		shifted.insert(
+			it.key() >= from ? it.key() + delta : it.key(), it.value());
+	}
+	m_items = shifted;
+
+	for (int& index : m_pendingCreate) {
+		if (index >= from) index += delta;
+	}
+}
+
+void SnapView::updateAncestorListeners() {
+	QQuickItem* content = QQuickFlickablePrivate::get(this)->contentItem;
+	QVector<QPointer<QQuickItem>> want;
+	if (content) want.append(content);
+	for (QQuickItem* it = parentItem(); it; it = it->parentItem())
+		want.append(it);
+
+	for (const QPointer<QQuickItem>& item :
+		 std::as_const(m_ancestorListeners)) {
+		if (item && !want.contains(item))
+			removeGeometryListener(item.data(), this);
+	}
+	for (const QPointer<QQuickItem>& item : std::as_const(want)) {
+		const bool known = std::any_of(
+			m_ancestorListeners.constBegin(),
+			m_ancestorListeners.constEnd(),
+			[&item](const QPointer<QQuickItem>& p) { return p == item; });
+		if (!known) addGeometryListener(item.data(), this);
+	}
+	m_ancestorListeners = want;
+
+	trackOriginResidual();
+}
+
+void SnapView::clearListeners() {
+	for (const QPointer<QQuickItem>& item : std::as_const(m_ancestorListeners))
+		removeGeometryListener(item.data(), this);
+	m_ancestorListeners.clear();
+	m_delegateListeners.clear();
+}
+
+void SnapView::connectModel() {
+	if (!m_model) return;
+	m_modelConnections.append(
+		QObject::connect(
+			m_model,
+			&QAbstractItemModel::rowsInserted,
+			this,
+			&SnapView::onRowsInserted));
+	m_modelConnections.append(
+		QObject::connect(
+			m_model,
+			&QAbstractItemModel::rowsAboutToBeRemoved,
+			this,
+			&SnapView::onRowsAboutToBeRemoved));
+	m_modelConnections.append(
+		QObject::connect(
+			m_model,
+			&QAbstractItemModel::rowsRemoved,
+			this,
+			&SnapView::onRowsRemoved));
+	m_modelConnections.append(
+		QObject::connect(
+			m_model,
+			&QAbstractItemModel::dataChanged,
+			this,
+			&SnapView::onDataChanged));
+	m_modelConnections.append(
+		QObject::connect(
+			m_model,
+			&QAbstractItemModel::modelReset,
+			this,
+			&SnapView::onModelReset));
+	m_modelConnections.append(
+		QObject::connect(
+			m_model, &QAbstractItemModel::layoutChanged, this, [this]() {
+				rebuildRows();
+				polish();
+			}));
+}
+
+void SnapView::disconnectModel() {
+	for (const auto& conn : std::as_const(m_modelConnections))
+		disconnect(conn);
+	m_modelConnections.clear();
+}
+
+void SnapView::onRowsInserted(const QModelIndex& parent, int first, int last) {
+	if (parent.isValid()) return;
+
+	// Delegates at or after the inserted range now address a different row, and
+	// the inserted rows have no measured size yet.
+	shiftDelegateIndices(first, last - first + 1);
+	m_rowSizes.resize(count());
+	for (int index = first; index <= last; ++index)
+		m_rowSizes[index] = 0.0;
+	rebuildRows();
+	polish();
+}
+
+void SnapView::onRowsAboutToBeRemoved(
+	const QModelIndex& parent, int first, int last) {
+	if (parent.isValid()) return;
+	for (int index = first; index <= last; ++index)
+		destroyDelegate(index);
+	m_rowSizes.remove(first, last - first + 1);
+	shiftDelegateIndices(last + 1, -(last - first + 1));
+}
+
+void SnapView::onRowsRemoved(const QModelIndex& parent, int first, int last) {
+	if (parent.isValid()) return;
+	Q_UNUSED(first)
+	Q_UNUSED(last)
+	rebuildRows();
+	polish();
+}
+
+void SnapView::onDataChanged(
+	const QModelIndex& topLeft, const QModelIndex& bottomRight) {
+	if (topLeft.parent().isValid() || bottomRight.parent().isValid()) return;
+	for (int index = topLeft.row(); index <= bottomRight.row(); ++index)
+		updateDelegateData(index);
+	// A row's content can change its size, so re-place as well.
+	polish();
+}
+
+void SnapView::onModelReset() {
+	for (int index : m_items.keys())
+		destroyDelegate(index);
+	m_sizeDevCache.clear();
+	m_rowSizes.clear();
+	rebuildRows();
+	polish();
+}
+
+} // namespace ZShell::components

Plugins/ZShell/Components/snapview.hpp

@@ -0,0 +1,237 @@
+#pragma once
+
+#include <QAbstractItemModel>
+#include <QHash>
+#include <QPointer>
+#include <QQmlComponent>
+#include <private/qquickflickable_p.h>
+#include <private/qquickitem_p.h>
+#include <qqmlintegration.h>
+
+class QTimer;
+
+namespace ZShell::components {
+
+// A ListView replacement that lays delegates out the way SnapLayout lays out
+// children: delegates are placed on device-pixel boundaries, the gaps between
+// them are whole device pixels, siblings that move together keep their relative
+// offsets, and a delegate that only moves is not resized. Like SnapLayout is to
+// RowLayout/ColumnLayout, this is to ListView: a Flickable with its own
+// placement, so there is no base-view positioner to fight with.
+//
+// Delegates receive `index` and `modelData` initial properties, so a delegate
+// declares `required property int index` and `required property var modelData`.
+// The cross-axis size (height in a horizontal view, width in a vertical one) is
+// set by the view, as ListView does; the main-axis size comes from the delegate
+// unless snapSizes is true.
+class SnapView : public QQuickFlickable, public QQuickItemChangeListener {
+	Q_OBJECT
+	QML_ELEMENT
+
+	Q_PROPERTY(
+		QAbstractItemModel* model READ model WRITE setModel NOTIFY modelChanged
+			FINAL)
+	Q_PROPERTY(
+		QQmlComponent* delegate READ delegate WRITE setDelegate NOTIFY
+			delegateChanged FINAL)
+
+	// Layout
+	Q_PROPERTY(
+		Qt::Orientation orientation READ orientation WRITE setOrientation NOTIFY
+			orientationChanged FINAL)
+	Q_PROPERTY(
+		qreal spacing READ spacing WRITE setSpacing NOTIFY spacingChanged FINAL)
+	Q_PROPERTY(
+		qreal cacheBuffer READ cacheBuffer WRITE setCacheBuffer NOTIFY
+			cacheBufferChanged FINAL)
+	Q_PROPERTY(
+		qreal estimatedSize READ estimatedSize WRITE setEstimatedSize NOTIFY
+			estimatedSizeChanged FINAL)
+
+	// Resize delegates to device pixels along the main axis too. Off by
+	// default, because delegates usually derive that size from their content
+	// and resizing them would break the binding. Placement is always
+	// device-pixel snapped.
+	Q_PROPERTY(
+		bool snapSizes READ snapSizes WRITE setSnapSizes NOTIFY snapSizesChanged
+			FINAL)
+
+	// Spread delegate creation over frames instead of creating everything in
+	// the first polish pass.
+	Q_PROPERTY(
+		bool asynchronous READ asynchronous WRITE setAsynchronous NOTIFY
+			asynchronousChanged FINAL)
+
+	// State
+	Q_PROPERTY(int count READ count NOTIFY countChanged FINAL)
+	Q_PROPERTY(
+		int currentIndex READ currentIndex WRITE setCurrentIndex NOTIFY
+			currentIndexChanged FINAL)
+	Q_PROPERTY(
+		QQuickItem* currentItem READ currentItem NOTIFY currentItemChanged FINAL)
+
+	signals:
+	void modelChanged();
+	void delegateChanged();
+	void orientationChanged();
+	void spacingChanged();
+	void cacheBufferChanged();
+	void estimatedSizeChanged();
+	void snapSizesChanged();
+	void asynchronousChanged();
+	void countChanged();
+	void currentIndexChanged();
+	void currentItemChanged();
+
+	public:
+	explicit SnapView(QQuickItem* parent = nullptr);
+	~SnapView() override;
+
+	[[nodiscard]] QAbstractItemModel* model() const;
+	void setModel(QAbstractItemModel* model);
+
+	[[nodiscard]] QQmlComponent* delegate() const;
+	void setDelegate(QQmlComponent* delegate);
+
+	[[nodiscard]] Qt::Orientation orientation() const;
+	void setOrientation(Qt::Orientation orientation);
+
+	[[nodiscard]] qreal spacing() const;
+	void setSpacing(qreal spacing);
+
+	[[nodiscard]] qreal cacheBuffer() const;
+	void setCacheBuffer(qreal buffer);
+
+	[[nodiscard]] qreal estimatedSize() const;
+	void setEstimatedSize(qreal size);
+
+	[[nodiscard]] bool snapSizes() const;
+	void setSnapSizes(bool snapSizes);
+
+	[[nodiscard]] bool asynchronous() const;
+	void setAsynchronous(bool asynchronous);
+
+	[[nodiscard]] int count() const;
+
+	[[nodiscard]] int currentIndex() const;
+	void setCurrentIndex(int index);
+
+	[[nodiscard]] QQuickItem* currentItem() const;
+
+	Q_INVOKABLE void positionViewAtBeginning();
+	Q_INVOKABLE void positionViewAtEnd();
+	Q_INVOKABLE void positionViewAtIndex(int index);
+
+	protected:
+	void componentComplete() override;
+	void geometryChange(
+		const QRectF& newGeometry, const QRectF& oldGeometry) override;
+	void updatePolish() override;
+	void itemChange(ItemChange change, const ItemChangeData& value) override;
+
+	// QQuickItemChangeListener
+	void itemGeometryChanged(
+		QQuickItem* item,
+		QQuickGeometryChange change,
+		const QRectF& oldGeometry) override;
+	void itemDestroyed(QQuickItem* item) override;
+
+	private:
+	struct Row {
+		qreal exactOffset = 0.0;
+		qreal exactSize = 0.0;
+	};
+
+	// Main-axis size last measured from a delegate, kept per model row so the
+	// content extent stays right while delegates outside the viewport are
+	// destroyed, the way ListView keeps contentHeight.
+	QVector<qreal> m_rowSizes;
+
+	// Placement, mirroring SnapLayout::arrangeChildren: exact positions come
+	// from cumulative row sizes, each near edge is rounded on its own so gaps
+	// stay whole device pixels, and siblings keep their relative offsets.
+	void layoutAndPlace();
+	void updateDelegates();
+	[[nodiscard]] QQuickItem* createDelegate(int index);
+	void destroyDelegate(int index);
+	void updateDelegateData(int index);
+
+	[[nodiscard]] qreal effectiveSpacing() const;
+	[[nodiscard]] qreal devicePixelRatio() const;
+	// Main-axis size of a row: the delegate's own size if it exists, otherwise
+	// the size cached when it was last visible, otherwise the estimate.
+	[[nodiscard]] qreal rowSize(int index) const;
+	[[nodiscard]] qint64 snappedDeviceMainSize(QQuickItem* item);
+	[[nodiscard]] int firstVisibleIndex() const;
+	[[nodiscard]] int lastVisibleIndex() const;
+	[[nodiscard]] QPointF contentOrigin() const;
+	void trackOriginResidual();
+
+	[[nodiscard]] QVariantMap delegateProperties(int index);
+	// The model's role names, cached because some models rebuild the hash on
+	// every call and this runs once per delegate per refresh.
+	[[nodiscard]] const QHash<int, QByteArray>& roleNames();
+	void invalidateRoleNames();
+
+	void rebuildRows();
+	// Sizes are measured along the main axis, so switching axis invalidates
+	// every cached size.
+	void invalidateMainAxisCaches();
+	// Re-keys the delegate map when rows shift, so an existing item keeps its
+	// place in the model instead of pointing at the wrong row.
+	void shiftDelegateIndices(int from, int delta);
+	void updateAncestorListeners();
+	void clearListeners();
+	void connectModel();
+	void disconnectModel();
+
+	void onRowsInserted(const QModelIndex& parent, int first, int last);
+	void onRowsAboutToBeRemoved(const QModelIndex& parent, int first, int last);
+	void onRowsRemoved(const QModelIndex& parent, int first, int last);
+	void onDataChanged(
+		const QModelIndex& topLeft, const QModelIndex& bottomRight);
+	void onModelReset();
+
+	QPointer<QAbstractItemModel> m_model;
+	QPointer<QQmlComponent> m_delegate;
+
+	Qt::Orientation m_orientation = Qt::Vertical;
+	qreal m_spacing = 0.0;
+	qreal m_cacheBuffer = 0.0;
+	qreal m_estimatedSize = -1.0;
+	bool m_snapSizes = false;
+	bool m_asynchronous = false;
+
+	int m_currentIndex = -1;
+
+	QVector<Row> m_rows;
+	QHash<int, QQuickItem*> m_items;
+	QVector<int> m_pendingCreate;
+
+	// Device-pixel main size of a delegate, so an item that only moves keeps
+	// the size it already has rather than re-rounding a drifting exact size.
+	QHash<QQuickItem*, qint64> m_sizeDevCache;
+
+	// Cached model role names; valid until the model or its roles change.
+	QHash<int, QByteArray> m_roleNames;
+	bool m_roleNamesValid = false;
+
+	// Fires the next asynchronous creation batch on the next event loop turn,
+	// so batches land on different frames instead of one polish flush.
+	QTimer* m_asyncTimer = nullptr;
+
+	// Items watched for sub-pixel moves. QPointer, as SnapLayout does, so a
+	// teardown order that destroys an item before the view cannot leave a
+	// dangling pointer to remove a listener from.
+	QVector<QPointer<QQuickItem>> m_delegateListeners;
+	QVector<QPointer<QQuickItem>> m_ancestorListeners;
+	qint64 m_originResidualX = -1;
+	qint64 m_originResidualY = -1;
+
+	bool m_placing = false;
+	bool m_componentComplete = false;
+
+	QList<QMetaObject::Connection> m_modelConnections;
+};
+
+} // namespace ZShell::components

Plugins/ZShell/Components/sparklinecontent.cpp

@@ -3,23 +3,120 @@
 #include <qmath.h>
 #include <qpainter.h>
 #include <qpen.h>
+#include <qquickwindow.h>
+
+#include <algorithm>
+#include <cmath>
 
 namespace ZShell::components {
 
+namespace {
+qint64 toDev(qreal logical, qreal dpr) {
+	return std::llround(logical * dpr);
+}
+
+qreal fromDev(qint64 device, qreal dpr) {
+	return qreal(device) / dpr;
+}
+
+// A line center whose device position leaves a whole-pixel-wide stroke: an even
+// width sits on pixel boundaries, an odd width on pixel centers. Same rule as
+// snapLine() in Components/LineGraph.qml.
+qreal snapLine(qreal logical, qint64 widthDev, qreal dpr) {
+	const qreal half = qreal(widthDev) / 2.0;
+	return (static_cast<qreal>(std::llround(logical * dpr - half)) + half) /
+		   dpr;
+}
+
+// y of a cubic bezier at targetX, found by bisection on the parameter. Used to
+// place one vertex per device pixel column, so a segment never interpolates its
+// edge across several columns.
+qreal cubicY(
+	const QPointF& p1,
+	const QPointF& c1,
+	const QPointF& c2,
+	const QPointF& p2,
+	qreal targetX) {
+	qreal lo = 0.0;
+	qreal hi = 1.0;
+	for (int it = 0; it < 16; ++it) {
+		const qreal t = (lo + hi) / 2.0;
+		const qreal u = 1.0 - t;
+		const qreal x = u * u * u * p1.x() + 3 * u * u * t * c1.x() +
+						3 * u * t * t * c2.x() + t * t * t * p2.x();
+		if (x < targetX)
+			lo = t;
+		else
+			hi = t;
+	}
+
+	const qreal t = (lo + hi) / 2.0;
+	const qreal u = 1.0 - t;
+	return u * u * u * p1.y() + 3 * u * u * t * c1.y() +
+		   3 * u * t * t * c2.y() + t * t * t * p2.y();
+}
+
+// Catmull-Rom controls with the control y clamped to the segment's own y span,
+// so a curve never overshoots past its endpoints.
+void segmentControls(
+	const QVector<QPointF>& points,
+	int i,
+	bool curveSmoothing,
+	QPointF& c1,
+	QPointF& c2) {
+	const QPointF& p0 = points[qMax(i - 1, 0)];
+	const QPointF& p1 = points[i];
+	const QPointF& p2 = points[i + 1];
+	const QPointF& p3 = points[qMin(i + 2, points.size() - 1)];
+
+	if (curveSmoothing && points.size() > 2) {
+		const qreal k = 1.0 / 6.0;
+		c1 = p1 + (p2 - p0) * k;
+		c2 = p2 - (p3 - p1) * k;
+
+		const qreal minY = qMin(p1.y(), p2.y());
+		const qreal maxY = qMax(p1.y(), p2.y());
+		c1.setY(qBound(minY, c1.y(), maxY));
+		c2.setY(qBound(minY, c2.y(), maxY));
+		return;
+	}
+
+	const qreal cx = (p1.x() + p2.x()) * 0.5;
+	c1 = QPointF(cx, p1.y());
+	c2 = QPointF(cx, p2.y());
+}
+} // namespace
+
 SparklineContent::SparklineContent(QQuickItem* parent)
 	: QQuickPaintedItem(parent) {
 	setAntialiasing(true);
 }
 
+void SparklineContent::itemChange(
+	ItemChange change, const ItemChangeData& value) {
+	QQuickPaintedItem::itemChange(change, value);
+	if (change == ItemSceneChange && value.window)
+		m_dpr = value.window->effectiveDevicePixelRatio();
+	else if (change == ItemDevicePixelRatioHasChanged && window())
+		m_dpr = window()->effectiveDevicePixelRatio();
+	else
+		return;
+
+	invalidate();
+}
+
 qreal SparklineContent::stepX() const {
 	if (m_historyLength < 2 || m_viewportW <= 0.0) return 0.0;
-	if (m_sliding) return m_viewportW / static_cast<qreal>(m_historyLength - 1);
-
 	const int len = qMax(
 		2,
 		(m_line1 && m_line1->count() >= 2) ? m_line1->count()
 										   : (m_line2 ? m_line2->count() : 2));
-	return m_viewportW / static_cast<qreal>(len - 1);
+	const qreal logical =
+		m_sliding ? m_viewportW / static_cast<qreal>(m_historyLength - 1)
+				  : m_viewportW / static_cast<qreal>(len - 1);
+	// A whole device pixel per step: every sample lands on a pixel column, and
+	// one slide step moves the content by an exact pixel count.
+	return fromDev((std::max)(qint64(1), toDev(logical, m_dpr)), m_dpr);
 }
 
 void SparklineContent::setViewportSize(
@@ -130,79 +227,97 @@ void SparklineContent::applyGeometry() {
 SparklineContent::LineGeometry SparklineContent::buildGeometry(
 	internal::CircularBuffer* buffer) const {
 	LineGeometry geom;
-	if (!buffer || buffer->count() < 2 || m_maxValue <= 0.0 ||
-		m_viewportW <= 0.0)
+	// Every input has to be a usable number: a NaN from QML (an animated maxValue
+	// fed by an empty buffer, for instance) would otherwise reach llround and the
+	// path stroker as garbage, which draws a shape that ignores the curve.
+	if (!buffer || buffer->count() < 2 || !std::isfinite(m_maxValue) ||
+		m_maxValue <= 0.0 || !std::isfinite(m_viewportW) ||
+		m_viewportW <= 0.0 || !std::isfinite(m_viewportH) || m_viewportH <= 0.0)
 		return geom;
 	if (m_historyLength < 2) return geom;
 
+	const qreal dpr = m_dpr > 0.0 ? m_dpr : 1.0;
 	const int len = buffer->count();
 	const qreal step = stepX();
-	if (step <= 0.0) return geom;
+	if (!std::isfinite(step) || step <= 0.0) return geom;
+
+	const qint64 stepDev = toDev(step, dpr);
+	const qint64 lineDev = std::isfinite(m_lineWidth)
+							   ? (std::max)(qint64(1), toDev(m_lineWidth, dpr))
+							   : qint64(1);
+	const qint64 heightDev = toDev(m_viewportH, dpr);
 
 	qreal startX = 0.0;
 	if (m_sliding)
 		startX = m_viewportW - (len - 1) * step + step;
 	else
 		startX = 0.0;
+	const qint64 startDev = toDev(startX, dpr);
 
-	const qreal h = m_viewportH;
-	const qreal strokePad = qCeil(m_lineWidth / 2);
-	const qreal curvePad = 3.0;
-	const qreal plotTop = strokePad + curvePad;
-	const qreal plotBottom = h - strokePad;
-	const qreal fillBottom = h;
-	const qreal plotH = qMax<qreal>(1.0, plotBottom - plotTop);
+	// Plot bounds in device pixels: half a stroke plus the curve overshoot at
+	// the top, a half stroke and one pixel of antialiasing feather at the
+	// bottom, so neither edge of the stroke is cut by the item's own rect.
+	const qint64 curvePadDev = toDev(m_curveSmoothing ? 3.0 : 0.0, dpr);
+	const qint64 plotTopDev = lineDev / 2 + curvePadDev;
+	const qint64 plotBottomDev =
+		(std::max)(plotTopDev + 1, heightDev - (lineDev + 1) / 2 - 1);
+	const qint64 plotHDev = plotBottomDev - plotTopDev;
+	const qreal fillBottom = fromDev(heightDev, dpr);
 
 	QVector<QPointF> points;
 	points.reserve(len);
 
 	for (int i = 0; i < len; ++i) {
-		const qreal value =
-			qBound<qreal>(0.0, buffer->smoothedAt(i), m_maxValue);
+		const qreal raw = buffer->smoothedAt(i);
 
-		const qreal x = startX + i * step;
-		const qreal y = plotTop + (1.0 - (value / m_maxValue)) * plotH;
-		points.append(QPointF(x, y));
+		// A non-finite sample poisons the whole path: llround of it is undefined,
+		// and the stroke and fill then ignore everything after that vertex. Treat
+		// it as no traffic instead.
+		const qreal value =
+			std::isfinite(raw) ? qBound<qreal>(0.0, raw, m_maxValue) : 0.0;
+
+		// Vertices on a pixel column, and on the y grid the stroke width needs.
+		// Item-local, so the parent's placement cannot move the shape. A flat run
+		// then lands on whole rows; slopes are interpolated, not snapped.
+		const qreal y = fromDev(
+			plotTopDev + static_cast<qint64>(std::llround(
+							 (1.0 - value / m_maxValue) *
+							 static_cast<double>(plotHDev))),
+			dpr);
+		points.append(QPointF(
+			fromDev(startDev + qint64(i) * stepDev, dpr),
+			snapLine(y, lineDev, dpr)));
 	}
 
 	QPainterPath linePath;
-	linePath.moveTo(points[0]);
+	linePath.moveTo(points.first());
 
-	if (m_curveSmoothing && points.size() > 2) {
-		const qreal tension = 1.0;
-		const qreal k = tension / 6.0;
-		const int n = static_cast<int>(points.size());
+	for (int i = 0; i < points.size() - 1; ++i) {
+		const QPointF& p1 = points[i];
+		const QPointF& p2 = points[i + 1];
+		QPointF c1;
+		QPointF c2;
+		segmentControls(points, i, m_curveSmoothing, c1, c2);
 
-		for (int i = 0; i < n - 1; ++i) {
-			const QPointF& p0 = points[qMax(i - 1, 0)];
-			const QPointF& p1 = points[i];
-			const QPointF& p2 = points[i + 1];
-			const QPointF& p3 = points[qMin(i + 2, n - 1)];
-
-			QPointF c1 = p1 + (p2 - p0) * k;
-			QPointF c2 = p2 - (p3 - p1) * k;
-
-			const qreal segMinY = qMin(p1.y(), p2.y());
-			const qreal segMaxY = qMax(p1.y(), p2.y());
-			c1.setY(qBound(segMinY, c1.y(), segMaxY));
-			c2.setY(qBound(segMinY, c2.y(), segMaxY));
-
-			linePath.cubicTo(c1, c2, p2);
-		}
-	} else {
-		for (int i = 0; i < points.size() - 1; ++i) {
-			const QPointF& p0 = points[i];
-			const QPointF& p1 = points[i + 1];
-			const qreal ctrlX = (p0.x() + p1.x()) * 0.5;
-			linePath.cubicTo(QPointF(ctrlX, p0.y()), QPointF(ctrlX, p1.y()), p1);
+		// One vertex per device pixel column, as Components/LineGraph.qml does: a
+		// segment spanning several columns would otherwise interpolate its edge
+		// across all of them. y stays continuous here - snapping it per column
+		// would step the slope one pixel at a time and read as a staircase.
+		const qint64 firstCol = std::llround(p1.x() * dpr) + 1;
+		const qint64 lastCol = std::llround(p2.x() * dpr) - 1;
+		for (qint64 col = firstCol; col <= lastCol; ++col) {
+			const qreal x = fromDev(col, dpr);
+			linePath.lineTo(x, cubicY(p1, c1, c2, p2, x));
 		}
+
+		linePath.lineTo(p2);
 	}
 
 	geom.stroke = linePath;
 
 	QPainterPath fillPath = linePath;
-	fillPath.lineTo(startX + (len - 1) * step, fillBottom);
-	fillPath.lineTo(startX, fillBottom);
+	fillPath.lineTo(points.last().x(), fillBottom);
+	fillPath.lineTo(points.first().x(), fillBottom);
 	fillPath.closeSubpath();
 	geom.fill = fillPath;
 	geom.hasData = true;
@@ -223,6 +338,12 @@ void SparklineContent::paint(QPainter* painter) {
 
 	painter->setRenderHint(QPainter::Antialiasing, true);
 
+	const qreal dpr = m_dpr > 0.0 ? m_dpr : 1.0;
+	const qreal lineWidth =
+		std::isfinite(m_lineWidth)
+			? fromDev((std::max)(qint64(1), toDev(m_lineWidth, dpr)), dpr)
+			: 1.0;
+
 	auto drawOne =
 		[&](const LineGeometry& geom, const QColor& color, qreal fillAlpha) {
 			if (!geom.hasData) return;
@@ -233,7 +354,7 @@ void SparklineContent::paint(QPainter* painter) {
 			painter->setBrush(fillColor);
 			painter->drawPath(geom.fill);
 
-			QPen pen(color, m_lineWidth);
+			QPen pen(color, lineWidth);
 			pen.setCapStyle(Qt::RoundCap);
 			pen.setJoinStyle(Qt::RoundJoin);
 			painter->setPen(pen);

Plugins/ZShell/Components/sparklinecontent.hpp

@@ -32,6 +32,11 @@ class SparklineContent : public QQuickPaintedItem {
 
 	[[nodiscard]] qreal stepX() const;
 
+	protected:
+	// The stroke width, sample spacing and plot bounds are quantized in device
+	// pixels, so they have to be built with the ratio the window actually has.
+	void itemChange(ItemChange change, const ItemChangeData& value) override;
+
 	private:
 	struct LineGeometry {
 		QPainterPath stroke;
@@ -60,6 +65,7 @@ class SparklineContent : public QQuickPaintedItem {
 
 	qreal m_viewportW = 0.0;
 	qreal m_viewportH = 0.0;
+	qreal m_dpr = 1.0;
 
 	LineGeometry m_geom1;
 	LineGeometry m_geom2;

Plugins/ZShell/Components/wavyline.cpp

@@ -1,5 +1,6 @@
 #include "wavyline.hpp"
 #include "wavylinerenderer.hpp"
+#include <QQuickWindow>
 
 namespace ZShell::controls {
 
@@ -25,6 +26,14 @@ QCanvasPainterItemRenderer* WavyLine::createItemRenderer() const {
 	return new WavyLineRenderer;
 }
 
+void WavyLine::itemChange(ItemChange change, const ItemChangeData& value) {
+	QCanvasPainterItem::itemChange(change, value);
+	if (change == ItemSceneChange && value.window)
+		m_dpr = value.window->effectiveDevicePixelRatio();
+	else if (change == ItemDevicePixelRatioHasChanged && window())
+		m_dpr = window()->effectiveDevicePixelRatio();
+}
+
 int WavyLine::lineWidth() const {
 	return m_lineWidth;
 }

Plugins/ZShell/Components/wavyline.hpp

@@ -103,6 +103,11 @@ class WavyLine : public QCanvasPainterItem {
 	[[nodiscard]] QCanvasPainterItemRenderer* createItemRenderer()
 		const override;
 
+	// Keeps the renderer's device pixel ratio current: strokes and sample
+	// spacing are quantized in device pixels, so they must be built with the
+	// ratio the window actually has.
+	void itemChange(ItemChange change, const ItemChangeData& value) override;
+
 	private:
 	friend class WavyLineRenderer;
 
@@ -118,6 +123,7 @@ class WavyLine : public QCanvasPainterItem {
 	qreal m_fullAngle;
 	qreal m_radius;
 	qreal m_value;
+	qreal m_dpr = 1.0;
 };
 
 } // namespace ZShell::controls

Plugins/ZShell/Components/wavylinerenderer.cpp

@@ -1,6 +1,8 @@
 #include "wavylinerenderer.hpp"
 #include "wavyline.hpp"
 #include <qcanvaspainter.h>
+#include <algorithm>
+#include <cmath>
 
 namespace ZShell::controls {
 
@@ -19,13 +21,48 @@ void WavyLineRenderer::synchronizeData(QCanvasPainterItem* item) {
 	m_fullAngle = wavyLine->m_fullAngle;
 	m_radius = wavyLine->m_radius;
 	m_value = wavyLine->m_value;
+	m_dpr = wavyLine->m_dpr > 0.0 ? wavyLine->m_dpr : 1.0;
 }
 
+namespace {
+qint64 toDev(qreal logical, qreal dpr) {
+	return std::llround(logical * dpr);
+}
+
+qreal fromDev(qint64 device, qreal dpr) {
+	return qreal(device) / dpr;
+}
+
+// A center coordinate whose device position shares the parity of the stroke's
+// device width: an even width centered on a pixel boundary and an odd width
+// centered on a pixel center are the two cases where both edges of the stroke
+// land on whole device pixels. Floored, so the caller gets the same value from
+// the same device size every time; a rounded half could flip between two grid
+// points depending on floating point noise.
+qreal snapCenterDev(qint64 sizeDev, qint64 widthDev) {
+	const double halfParity = (widthDev % 2) == 0 ? 0.0 : 0.5;
+	return std::floor(static_cast<double>(sizeDev) / 2.0 - halfParity)
+		+ halfParity;
+}
+
+qint64 snapAmplitude(qint64 widthDev, qreal multiplier) {
+	return std::llround(static_cast<double>(widthDev) * multiplier);
+}
+} // namespace
+
 void WavyLineRenderer::paint(QCanvasPainter* painter) {
 	painter->clearRect(0, 0, width(), height());
 
+	// The stroke is quantized in the item's own device pixel space, never
+	// against its position: the parent layout already places the item on the
+	// device grid, so a local whole-device value stays whole-device wherever
+	// the item moves, and a move cannot change the painted path.
+	const qreal dpr = m_dpr;
+	m_lineWidthDev = (std::max)(qint64(1), toDev(m_lineWidth, dpr));
+	m_amplitudeDev = snapAmplitude(m_lineWidthDev, m_amplitudeMultiplier);
+
 	painter->setStrokeStyle(m_color);
-	painter->setLineWidth(m_lineWidth);
+	painter->setLineWidth(fromDev(m_lineWidthDev, dpr));
 	painter->setLineCap(QCanvasPainter::LineCap::Round);
 
 	if (m_pathType == WavyLine::Arc) {
@@ -36,18 +73,36 @@ void WavyLineRenderer::paint(QCanvasPainter* painter) {
 }
 
 void WavyLineRenderer::paintLinear(QCanvasPainter* painter) {
-	const auto amplitude = m_lineWidth * m_amplitudeMultiplier;
+	const qreal dpr = m_dpr;
+	const auto lineWidth = fromDev(m_lineWidthDev, dpr);
 	const auto phase = m_waveProgress * 2 * M_PI;
-	const auto centerY = height() / 2;
+	const qint64 heightDev = toDev(height(), dpr);
+	const qreal cyDev = snapCenterDev(heightDev, m_lineWidthDev);
+	const auto centerY = cyDev / dpr;
 	const auto len = m_fullLength > 0 ? m_fullLength : 1;
-	const auto start = m_lineWidth / 2.0;
-	const auto fullEnd = width() - m_lineWidth / 2.0;
+	const auto start = lineWidth / 2.0;
+	const auto fullEnd = width() - lineWidth / 2.0;
 	const auto drawEnd = start + (fullEnd - start) * m_value;
 
+	// Keep the crest inside the item's own texture, with one device pixel for
+	// the antialiasing feather, so a tight item cannot cut it flat.
+	const qint64 halfDev = (m_lineWidthDev + 1) / 2;
+	const qint64 roomDev = static_cast<qint64>(
+		std::floor((std::min)(cyDev, qreal(heightDev) - cyDev)));
+	const qint64 amplitudeDev = (std::max)(qint64(0), roomDev - halfDev - 1);
+	const auto amplitude =
+		fromDev((std::min)(m_amplitudeDev, amplitudeDev), dpr);
+
 	painter->beginPath();
 
 	bool first = true;
-	for (int x = m_lineWidth / 2; x <= drawEnd; ++x) {
+	// One vertex per device pixel column. A segment spanning several columns
+	// interpolates its edge across all of them, which is what makes a sloped
+	// stroke look soft rather than crisply anti-aliased.
+	const qint64 firstCol = toDev(start, dpr);
+	const qint64 lastCol = toDev(drawEnd, dpr);
+	for (qint64 col = firstCol; col <= lastCol; ++col) {
+		const auto x = fromDev(col, dpr);
 		const auto theta =
 			m_frequency * 2 * M_PI * (x + m_startX) / len + phase;
 		const auto waveY = centerY + amplitude * qSin(theta);
@@ -67,16 +122,44 @@ void WavyLineRenderer::paintArc(QCanvasPainter* painter) {
 		return;
 	}
 
+	const qreal dpr = m_dpr;
+	const auto amplitude = fromDev(m_amplitudeDev, dpr);
 	const auto startAngleRad = m_startAngle * M_PI / 180.0;
 	const auto fullAngleRad = m_fullAngle * M_PI / 180.0;
 
-	const auto amplitude = m_lineWidth * m_amplitudeMultiplier;
-	const auto cx = width() / 2.0;
-	const auto cy = height() / 2.0;
-	const auto radius =
-		m_radius > 0
-			? m_radius
-			: (qMin(width(), height()) - m_lineWidth - 2 * amplitude) / 2.0;
+	// The center comes from the item's own device size and the stroke parity,
+	// the same rule Components/CircularProgress.qml applies to its background
+	// Shape arc, so the two rings share one center.
+	const qint64 widthDev = toDev(width(), dpr);
+	const qint64 heightDev = toDev(height(), dpr);
+	const qreal cxDev = snapCenterDev(widthDev, m_lineWidthDev);
+	const qreal cyDev = snapCenterDev(heightDev, m_lineWidthDev);
+	const auto cx = cxDev / dpr;
+	const auto cy = cyDev / dpr;
+
+	// The path is painted into a texture exactly the item's size, so anything
+	// past its edge is cut flat. Keep the outer stroke edge, plus the wave
+	// crest, inside that rect and leave one device pixel for the antialiasing
+	// feather. Derived from the item's own size and its local center, so it
+	// does not depend on where the item is placed.
+	const qint64 halfDev = (m_lineWidthDev + 1) / 2;
+	const qint64 roomDev = static_cast<qint64>(
+		std::floor((std::min)((std::min)(cxDev, qreal(widthDev) - cxDev),
+							  (std::min)(cyDev, qreal(heightDev) - cyDev))));
+	const qint64 maxRadiusDev = roomDev - m_amplitudeDev - halfDev - 1;
+
+	// The radius is a whole device pixel count. Derived from the item's own
+	// device size, so it does not depend on where the item is.
+	qint64 radiusDev;
+	if (m_radius > 0) {
+		radiusDev = toDev(m_radius, dpr);
+	} else {
+		const qint64 inner = (std::min)(widthDev, heightDev) - m_lineWidthDev -
+							 2 * m_amplitudeDev;
+		radiusDev = (std::max)(qint64(1), inner / 2);
+	}
+	radiusDev = (std::max)(qint64(1), (std::min)(radiusDev, maxRadiusDev));
+	const auto radius = fromDev(radiusDev, dpr);
 
 	if (radius <= 0) {
 		return;
@@ -91,7 +174,11 @@ void WavyLineRenderer::paintArc(QCanvasPainter* painter) {
 		return;
 	}
 
-	const auto N = qMax(64, qCeil(radius * drawAngleRad));
+	// Sample every device pixel of arc length, not every logical one: at a
+	// fractional ratio a logical step is more than one device pixel wide, and
+	// the edge would then be interpolated across the pixels it crosses.
+	const auto N =
+		qMax(64, qCeil(static_cast<double>(toDev(radius, dpr)) * drawAngleRad));
 	const auto dTheta = drawAngleRad / N;
 
 	painter->beginPath();

Plugins/ZShell/Components/wavylinerenderer.hpp

@@ -27,6 +27,9 @@ class WavyLineRenderer final : public QCanvasPainterItemRenderer {
 	qreal m_fullAngle;
 	qreal m_radius;
 	qreal m_value;
+	qreal m_dpr = 1.0;
+	qint64 m_lineWidthDev = 4;
+	qint64 m_amplitudeDev = 0;
 };
 
 } // namespace ZShell::controls