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Merged
bryankeller merged 1 commit into from
Jun 9, 2026
Merged

Bk/performance optimizations 2 #159

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243 changes: 188 additions & 55 deletions MagazineLayout/LayoutCore/ModelState.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -223,11 +223,10 @@ final class ModelState {
}

var itemFrame: CGRect!
mutateSectionModels(
withUnsafeMutableBufferPointer: { directlyMutableSectionModels in
itemFrame = directlyMutableSectionModels[itemLocation.sectionIndex].calculateFrameForItem(
atIndex: itemLocation.elementIndex)
})
sectionModels.withUnsafeMutableBufferPointer { sectionModels in
itemFrame = sectionModels[itemLocation.sectionIndex].calculateFrameForItem(
atIndex: itemLocation.elementIndex)
}

itemFrame.origin.y += sectionMinY
return itemFrame
Expand All @@ -243,15 +242,14 @@ final class ModelState {

let currentVisibleBounds = currentVisibleBoundsProvider()
var headerFrame: CGRect?
mutateSectionModels(
withUnsafeMutableBufferPointer: { directlyMutableSectionModels in
headerFrame = directlyMutableSectionModels[sectionIndex].calculateFrameForHeader(
inSectionVisibleBounds: CGRect(
x: currentVisibleBounds.minX,
y: currentVisibleBounds.minY - sectionMinY,
width: currentVisibleBounds.width,
height: currentVisibleBounds.height))
})
sectionModels.withUnsafeMutableBufferPointer { sectionModels in
headerFrame = sectionModels[sectionIndex].calculateFrameForHeader(
inSectionVisibleBounds: CGRect(
x: currentVisibleBounds.minX,
y: currentVisibleBounds.minY - sectionMinY,
width: currentVisibleBounds.width,
height: currentVisibleBounds.height))
}

headerFrame?.origin.y += sectionMinY
return headerFrame
Expand All @@ -267,15 +265,14 @@ final class ModelState {

let currentVisibleBounds = currentVisibleBoundsProvider()
var footerFrame: CGRect?
mutateSectionModels(
withUnsafeMutableBufferPointer: { directlyMutableSectionModels in
footerFrame = directlyMutableSectionModels[sectionIndex].calculateFrameForFooter(
sectionModels.withUnsafeMutableBufferPointer { sectionModels in
footerFrame = sectionModels[sectionIndex].calculateFrameForFooter(
inSectionVisibleBounds: CGRect(
x: currentVisibleBounds.minX,
y: currentVisibleBounds.minY - sectionMinY,
width: currentVisibleBounds.width,
height: currentVisibleBounds.height))
})
}

footerFrame?.origin.y += sectionMinY
return footerFrame
Expand All @@ -290,10 +287,9 @@ final class ModelState {
}

var backgroundFrame: CGRect?
mutateSectionModels(
withUnsafeMutableBufferPointer: { directlyMutableSectionModels in
backgroundFrame = directlyMutableSectionModels[sectionIndex].calculateFrameForBackground()
})
sectionModels.withUnsafeMutableBufferPointer { sectionModels in
backgroundFrame = sectionModels[sectionIndex].calculateFrameForBackground()
}

backgroundFrame?.origin.y += sectionMinY
return backgroundFrame
Expand Down Expand Up @@ -357,11 +353,34 @@ final class ModelState {
invalidateSectionMaxYsCacheForSectionIndices(startingAt: sectionIndex)
}

func updateMetrics(
to sectionMetrics: MagazineLayoutSectionMetrics,
forSectionAtIndex sectionIndex: Int,
sectionModel: inout SectionModel)
{
let didUpdate = sectionModel.updateMetrics(to: sectionMetrics)
if didUpdate {
invalidateSectionMaxYsCacheForSectionIndices(startingAt: sectionIndex)
}
}

func updateMetrics(
to sectionMetrics: MagazineLayoutSectionMetrics,
forSectionAtIndex sectionIndex: Int)
{
sectionModels[sectionIndex].updateMetrics(to: sectionMetrics)

invalidateSectionMaxYsCacheForSectionIndices(startingAt: sectionIndex)
}

func updateItemSizeModes(
forSectionAtIndex sectionIndex: Int,
sectionModel: inout SectionModel,
sizeModeProvider: (_ itemIndex: Int) -> MagazineLayoutItemSizeMode)
{
sectionModel.updateItemSizeModes(sizeModeProvider)

// TODO: Only invalidate if something changes
invalidateSectionMaxYsCacheForSectionIndices(startingAt: sectionIndex)
}

Expand All @@ -371,6 +390,19 @@ final class ModelState {
invalidateSectionMaxYsCacheForSectionIndices(startingAt: indexPath.section)
}

func setHeader(
_ headerModel: HeaderModel,
forSectionAtIndex sectionIndex: Int,
sectionModel: inout SectionModel)
{
sectionModel.setHeader(headerModel)

// TODO: Only invalidate if something changes
invalidateSectionMaxYsCacheForSectionIndices(startingAt: sectionIndex)

prepareElementLocationsForFlattenedIndices()
}

func setHeader(_ headerModel: HeaderModel, forSectionAtIndex sectionIndex: Int) {
sectionModels[sectionIndex].setHeader(headerModel)

Expand All @@ -379,13 +411,33 @@ final class ModelState {
prepareElementLocationsForFlattenedIndices()
}

func removeHeader(forSectionAtIndex sectionIndex: Int, sectionModel: inout SectionModel) {
if sectionModel.removeHeader() {
invalidateSectionMaxYsCacheForSectionIndices(startingAt: sectionIndex)
prepareElementLocationsForFlattenedIndices()
}
}

func removeHeader(forSectionAtIndex sectionIndex: Int) {
if sectionModels[sectionIndex].removeHeader() {
invalidateSectionMaxYsCacheForSectionIndices(startingAt: sectionIndex)
prepareElementLocationsForFlattenedIndices()
}
}

func setFooter(
_ footerModel: FooterModel,
forSectionAtIndex sectionIndex: Int,
sectionModel: inout SectionModel)
{
sectionModel.setFooter(footerModel)

// TODO: Only invalidate if something changes
invalidateSectionMaxYsCacheForSectionIndices(startingAt: sectionIndex)

prepareElementLocationsForFlattenedIndices()
}

func setFooter(_ footerModel: FooterModel, forSectionAtIndex sectionIndex: Int) {
sectionModels[sectionIndex].setFooter(footerModel)

Expand All @@ -394,19 +446,43 @@ final class ModelState {
prepareElementLocationsForFlattenedIndices()
}

func removeFooter(forSectionAtIndex sectionIndex: Int, sectionModel: inout SectionModel) {
if sectionModel.removeFooter() {
invalidateSectionMaxYsCacheForSectionIndices(startingAt: sectionIndex)
prepareElementLocationsForFlattenedIndices()
}
}

func removeFooter(forSectionAtIndex sectionIndex: Int) {
if sectionModels[sectionIndex].removeFooter() {
invalidateSectionMaxYsCacheForSectionIndices(startingAt: sectionIndex)
prepareElementLocationsForFlattenedIndices()
}
}

func setBackground(
_ backgroundModel: BackgroundModel,
forSectionAtIndex sectionIndex: Int,
sectionModel: inout SectionModel)
{
sectionModel.setBackground(backgroundModel)

// TODO: Only invalidate if something changes
prepareElementLocationsForFlattenedIndices()
}

func setBackground(_ backgroundModel: BackgroundModel, forSectionAtIndex sectionIndex: Int) {
sectionModels[sectionIndex].setBackground(backgroundModel)

prepareElementLocationsForFlattenedIndices()
}

func removeBackground(forSectionAtIndex sectionIndex: Int, sectionModel: inout SectionModel) {
if sectionModel.removeBackground() {
prepareElementLocationsForFlattenedIndices()
}
}

func removeBackground(forSectionAtIndex sectionIndex: Int) {
if sectionModels[sectionIndex].removeBackground() {
prepareElementLocationsForFlattenedIndices()
Expand Down Expand Up @@ -497,6 +573,16 @@ final class ModelState {
itemIndexPathsToDelete.removeAll()
}

func forEachSectionModel(
_ mutator: (_ sectionIndex: Int, _ sectionModel: inout SectionModel) -> Void)
{
sectionModels.withUnsafeMutableBufferPointer { sectionModels in
for sectionIndex in 0..<sectionModels.count {
mutator(sectionIndex, &sectionModels[sectionIndex])
}
}
}

// MARK: Private

private let currentVisibleBoundsProvider: () -> CGRect
Expand All @@ -510,13 +596,6 @@ final class ModelState {
private var backgroundLocationsForFlattenedIndices = [Int: ElementLocation]()
private var itemLocationsForFlattenedIndices = [Int: ElementLocation]()

private func mutateSectionModels(
withUnsafeMutableBufferPointer body: (inout UnsafeMutableBufferPointer<SectionModel>) -> Void)
{
// Accessing these arrays using unsafe, untyped (raw) pointers
// avoids expensive copy-on-writes and Swift retain / release calls.
sectionModels.withUnsafeMutableBufferPointer(body)
}
Comment on lines -513 to -519

@bryankeller bryankeller Jun 9, 2026

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no reason for this helper


private func prepareElementLocationsForFlattenedIndices() {
headerLocationsForFlattenedIndices.removeAll()
Expand Down Expand Up @@ -696,29 +775,55 @@ final class ModelState {
return
}

for sectionIndex in sectionIndex..<sectionMaxYsCache.count {
sectionMaxYsCache[sectionIndex] = nil
if MagazineLayout._enableExperimentalOptimizations {
sectionMaxYsCache.withUnsafeMutableBufferPointer { sectionMaxYsCache in
for sectionIndex in sectionIndex..<sectionMaxYsCache.count {
sectionMaxYsCache[sectionIndex] = nil
}
}
} else {
for sectionIndex in sectionIndex..<sectionMaxYsCache.count {
sectionMaxYsCache[sectionIndex] = nil
}
}
}

private func reloadSectionModels(
sectionModelReloadIndexPairs: [(sectionModel: SectionModel, reloadIndex: Int)])
{
for (sectionModel, reloadIndex) in sectionModelReloadIndexPairs {
sectionModels.remove(at: reloadIndex)
sectionModels.insert(sectionModel, at: reloadIndex)
if MagazineLayout._enableExperimentalOptimizations {
sectionModels.withUnsafeMutableBufferPointer { sectionModels in
for (sectionModel, reloadIndex) in sectionModelReloadIndexPairs {
sectionModels[reloadIndex] = sectionModel
}
}
} else {
for (sectionModel, reloadIndex) in sectionModelReloadIndexPairs {
sectionModels.remove(at: reloadIndex)
sectionModels.insert(sectionModel, at: reloadIndex)
}
}
}

private func reloadItemModels(
itemModelReloadIndexPathPairs: [(itemModel: ItemModel, reloadIndexPath: IndexPath)])
{
for (itemModel, reloadIndexPath) in itemModelReloadIndexPathPairs {
sectionModels[reloadIndexPath.section].deleteItemModel(
atIndex: reloadIndexPath.item)
sectionModels[reloadIndexPath.section].insert(
itemModel, atIndex:
reloadIndexPath.item)
if MagazineLayout._enableExperimentalOptimizations {
sectionModels.withUnsafeMutableBufferPointer { sectionModels in
for (itemModel, reloadIndexPath) in itemModelReloadIndexPathPairs {
sectionModels[reloadIndexPath.section].updateItemModel(
atIndex: reloadIndexPath.item,
to: itemModel)
}
}
} else {
for (itemModel, reloadIndexPath) in itemModelReloadIndexPathPairs {
sectionModels[reloadIndexPath.section].deleteItemModel(
atIndex: reloadIndexPath.item)
sectionModels[reloadIndexPath.section].insert(
itemModel,
atIndex: reloadIndexPath.item)
}
}
}

Expand All @@ -731,9 +836,18 @@ final class ModelState {

private func deleteItemModels(atIndexPaths indexPathsOfItemModelsToDelete: [IndexPath]) {
// Always delete in descending order
for indexPathOfItemModelToDelete in (indexPathsOfItemModelsToDelete.sorted { $0 > $1 }) {
sectionModels[indexPathOfItemModelToDelete.section].deleteItemModel(
atIndex: indexPathOfItemModelToDelete.item)
if MagazineLayout._enableExperimentalOptimizations {
sectionModels.withUnsafeMutableBufferPointer { sectionModels in
for indexPathOfItemModelToDelete in (indexPathsOfItemModelsToDelete.sorted { $0 > $1 }) {
sectionModels[indexPathOfItemModelToDelete.section].deleteItemModel(
atIndex: indexPathOfItemModelToDelete.item)
}
}
} else {
for indexPathOfItemModelToDelete in (indexPathsOfItemModelsToDelete.sorted { $0 > $1 }) {
sectionModels[indexPathOfItemModelToDelete.section].deleteItemModel(
atIndex: indexPathOfItemModelToDelete.item)
}
}
}

Expand All @@ -750,18 +864,37 @@ final class ModelState {
itemModelInsertIndexPathPairs: [(itemModel: ItemModel, insertIndexPath: IndexPath)])
{
// Always insert in ascending order
for (itemModel, insertIndexPath) in (itemModelInsertIndexPathPairs.sorted { $0.insertIndexPath < $1.insertIndexPath }) {
let sectionIndex = insertIndexPath.section
let itemIndex = insertIndexPath.item
let section = sectionModels[sectionIndex]
if itemIndex < section.numberOfItems, itemModel.id == section.idForItemModel(atIndex: itemIndex) {
// If the `itemModel` to insert already exists at the destination index, then there's no need to insert it again. This
// happens if item move updates are generated in addition to section move updates, which appears to be the case when using
// `UICollectionViewDiffableDataSource`. Other diffing approaches, like Paul Heckel's, do not produce item moves when
// their containing sections move.
continue
} else {
sectionModels[insertIndexPath.section].insert(itemModel, atIndex: itemIndex)
if MagazineLayout._enableExperimentalOptimizations {
sectionModels.withUnsafeMutableBufferPointer { sectionModels in
for (itemModel, insertIndexPath) in (itemModelInsertIndexPathPairs.sorted { $0.insertIndexPath < $1.insertIndexPath }) {
let sectionIndex = insertIndexPath.section
let itemIndex = insertIndexPath.item
let section = sectionModels[sectionIndex]
if itemIndex < section.numberOfItems, itemModel.id == section.idForItemModel(atIndex: itemIndex) {
// If the `itemModel` to insert already exists at the destination index, then there's no need to insert it again. This
// happens if item move updates are generated in addition to section move updates, which appears to be the case when using
// `UICollectionViewDiffableDataSource`. Other diffing approaches, like Paul Heckel's, do not produce item moves when
// their containing sections move.
continue
} else {
sectionModels[insertIndexPath.section].insert(itemModel, atIndex: itemIndex)
}
}
}
} else {
for (itemModel, insertIndexPath) in (itemModelInsertIndexPathPairs.sorted { $0.insertIndexPath < $1.insertIndexPath }) {
let sectionIndex = insertIndexPath.section
let itemIndex = insertIndexPath.item
let section = sectionModels[sectionIndex]
if itemIndex < section.numberOfItems, itemModel.id == section.idForItemModel(atIndex: itemIndex) {
// If the `itemModel` to insert already exists at the destination index, then there's no need to insert it again. This
// happens if item move updates are generated in addition to section move updates, which appears to be the case when using
// `UICollectionViewDiffableDataSource`. Other diffing approaches, like Paul Heckel's, do not produce item moves when
// their containing sections move.
continue
} else {
sectionModels[insertIndexPath.section].insert(itemModel, atIndex: itemIndex)
}
Comment on lines +867 to +897

@bryankeller bryankeller Jun 9, 2026

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nothing new here, just copy and pasted into two branches so we can safely test

}
}
}
Expand Down
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