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

Optimize data structures and defer layout work #160

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4 changes: 4 additions & 0 deletions MagazineLayout.xcodeproj/project.pbxproj
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -39,6 +39,7 @@
93A1C04E21ACED1100DED67D /* ElementLocationFramePairsTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 93A1C00F21ACED0100DED67D /* ElementLocationFramePairsTests.swift */; };
93A1C04F21ACED1100DED67D /* ModelStateUpdateTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 93A1C01021ACED0100DED67D /* ModelStateUpdateTests.swift */; };
93A868552EE0D7870027691E /* IDGenerator.swift in Sources */ = {isa = PBXBuildFile; fileRef = 93A868542EE0D7870027691E /* IDGenerator.swift */; };
93F8D8B22FD38BBF005325C0 /* Array+SafeSubscript.swift in Sources */ = {isa = PBXBuildFile; fileRef = 93F8D8B12FD38BBF005325C0 /* Array+SafeSubscript.swift */; };
93F8DAE62FD76026005325C0 /* Signposting.swift in Sources */ = {isa = PBXBuildFile; fileRef = 93F8DAE52FD76026005325C0 /* Signposting.swift */; };
FCAC642622085AF100973F4C /* MagazineLayoutHeaderVisibilityMode.swift in Sources */ = {isa = PBXBuildFile; fileRef = FCAC642522085AF100973F4C /* MagazineLayoutHeaderVisibilityMode.swift */; };
FCAC642822085B0E00973F4C /* FooterModel.swift in Sources */ = {isa = PBXBuildFile; fileRef = FCAC642722085B0E00973F4C /* FooterModel.swift */; };
Expand Down Expand Up @@ -97,6 +98,7 @@
93A1C05321ACEDFC00DED67D /* LICENSE */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text; path = LICENSE; sourceTree = SOURCE_ROOT; };
93A1C05421ACEDFC00DED67D /* README.md */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = net.daringfireball.markdown; path = README.md; sourceTree = SOURCE_ROOT; };
93A868542EE0D7870027691E /* IDGenerator.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = IDGenerator.swift; sourceTree = "<group>"; };
93F8D8B12FD38BBF005325C0 /* Array+SafeSubscript.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = "Array+SafeSubscript.swift"; sourceTree = "<group>"; };
93F8DAE52FD76026005325C0 /* Signposting.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Signposting.swift; sourceTree = "<group>"; };
FCAC642522085AF100973F4C /* MagazineLayoutHeaderVisibilityMode.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = MagazineLayoutHeaderVisibilityMode.swift; sourceTree = "<group>"; };
FCAC642722085B0E00973F4C /* FooterModel.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = FooterModel.swift; sourceTree = "<group>"; };
Expand Down Expand Up @@ -234,6 +236,7 @@
FDABC2572B23D0A000C9B8EF /* TargetContentOffsetAnchor.swift */,
FD244FEE28B41F9900046C0D /* UITraitCollection+DisplayScale.swift */,
93A868542EE0D7870027691E /* IDGenerator.swift */,
93F8D8B12FD38BBF005325C0 /* Array+SafeSubscript.swift */,
);
path = Types;
sourceTree = "<group>";
Expand Down Expand Up @@ -362,6 +365,7 @@
FCAC642822085B0E00973F4C /* FooterModel.swift in Sources */,
93A1C03C21ACED0100DED67D /* UICollectionViewDelegateMagazineLayout.swift in Sources */,
93A1C03721ACED0100DED67D /* MagazineLayoutItemSizeMode.swift in Sources */,
93F8D8B22FD38BBF005325C0 /* Array+SafeSubscript.swift in Sources */,
FD4DFF0A21B0D182001F46CE /* MagazineLayoutCollectionReusableView.swift in Sources */,
93A1C04321ACED0100DED67D /* MagazineLayoutItemWidthMode+WidthDivisor.swift in Sources */,
93A1C03D21ACED0100DED67D /* MagazineLayout+Default.swift in Sources */,
Expand Down
213 changes: 169 additions & 44 deletions MagazineLayout/LayoutCore/ModelState.swift
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -134,18 +134,24 @@ final class ModelState {
}

func itemLocationFramePairs(forItemsIn rect: CGRect) -> ElementLocationFramePairs {
prepareElementLocationsForFlattenedIndicesIfNeeded()

return elementLocationFramePairsForElements(
in: rect,
withElementLocationsForFlattenedIndices: itemLocationsForFlattenedIndices,
newElementLocationsForFlattenedIndices: newItemLocationsForFlattenedIndices,
andFramesProvidedBy: { itemLocation -> CGRect in
return frameForItem(at: itemLocation)
})
}

func headerLocationFramePairs(forHeadersIn rect: CGRect) -> ElementLocationFramePairs {
prepareElementLocationsForFlattenedIndicesIfNeeded()

return elementLocationFramePairsForElements(
in: rect,
withElementLocationsForFlattenedIndices: headerLocationsForFlattenedIndices,
newElementLocationsForFlattenedIndices: newHeaderLocationsForFlattenedIndices,
andFramesProvidedBy: { headerLocation -> CGRect in
guard
let headerFrame = frameForHeader(
Expand All @@ -160,9 +166,12 @@ final class ModelState {
}

func footerLocationFramePairs(forFootersIn rect: CGRect) -> ElementLocationFramePairs {
prepareElementLocationsForFlattenedIndicesIfNeeded()

return elementLocationFramePairsForElements(
in: rect,
withElementLocationsForFlattenedIndices: footerLocationsForFlattenedIndices,
newElementLocationsForFlattenedIndices: newFooterLocationsForFlattenedIndices,
andFramesProvidedBy: { footerLocation -> CGRect in
guard
let footerFrame = frameForFooter(
Expand All @@ -177,9 +186,12 @@ final class ModelState {
}

func backgroundLocationFramePairs(forBackgroundsIn rect: CGRect) -> ElementLocationFramePairs {
prepareElementLocationsForFlattenedIndicesIfNeeded()

return elementLocationFramePairsForElements(
in: rect,
withElementLocationsForFlattenedIndices: backgroundLocationsForFlattenedIndices,
newElementLocationsForFlattenedIndices: newBackgroundLocationsForFlattenedIndices,
andFramesProvidedBy: { backgroundLocation -> CGRect in
guard
let backgroundFrame = frameForBackground(
Expand All @@ -194,15 +206,25 @@ final class ModelState {
}

func sectionMaxY(forSectionAtIndex targetSectionIndex: Int) -> CGFloat {
flushSectionMaxYsCacheInvalidationIfNeeded()

var sectionMaxY: CGFloat {
guard targetSectionIndex >= 0 && targetSectionIndex < numberOfSections else {
assertionFailure("`targetSectionIndex` is not within the bounds of the section models array")
return 0
}

var totalHeight: CGFloat = 0
for sectionIndex in 0...targetSectionIndex {
totalHeight += sectionModels[sectionIndex].calculateHeight()
if MagazineLayout._enableExperimentalOptimizations {
sectionModels.withUnsafeMutableBufferPointer { sectionModels in
for sectionIndex in 0...targetSectionIndex {
totalHeight += sectionModels[sectionIndex].calculateHeight()
}
}
} else {
for sectionIndex in 0...targetSectionIndex {
totalHeight += sectionModels[sectionIndex].calculateHeight()
}
}

return totalHeight
Expand Down Expand Up @@ -299,10 +321,19 @@ final class ModelState {
let currentVisibleBounds = currentVisibleBoundsProvider()
let newModelState = ModelState(currentVisibleBoundsProvider: { currentVisibleBounds })
newModelState.sectionModels = sectionModels

prepareElementLocationsForFlattenedIndicesIfNeeded()

newModelState.headerLocationsForFlattenedIndices = headerLocationsForFlattenedIndices
newModelState.footerLocationsForFlattenedIndices = footerLocationsForFlattenedIndices
newModelState.backgroundLocationsForFlattenedIndices = backgroundLocationsForFlattenedIndices
newModelState.itemLocationsForFlattenedIndices = itemLocationsForFlattenedIndices

newModelState.newHeaderLocationsForFlattenedIndices = newHeaderLocationsForFlattenedIndices
newModelState.newFooterLocationsForFlattenedIndices = newFooterLocationsForFlattenedIndices
newModelState.newBackgroundLocationsForFlattenedIndices = newBackgroundLocationsForFlattenedIndices
newModelState.newItemLocationsForFlattenedIndices = newItemLocationsForFlattenedIndices

return newModelState
}

Expand Down Expand Up @@ -596,51 +627,105 @@ final class ModelState {
private var backgroundLocationsForFlattenedIndices = [Int: ElementLocation]()
private var itemLocationsForFlattenedIndices = [Int: ElementLocation]()

private var newHeaderLocationsForFlattenedIndices = [ElementLocation]()
private var newFooterLocationsForFlattenedIndices = [ElementLocation]()
private var newBackgroundLocationsForFlattenedIndices = [ElementLocation]()
private var newItemLocationsForFlattenedIndices = [ElementLocation]()

// When experimental optimizations are enabled, these defer the corresponding bookkeeping work
// until the next read that depends on it, coalescing repeated invalidations during a single
// round of section model mutations.
private var needsPrepareElementLocationsForFlattenedIndices = false
private var firstInvalidatedSectionMaxYIndex: Int?

private func prepareElementLocationsForFlattenedIndices() {
headerLocationsForFlattenedIndices.removeAll()
footerLocationsForFlattenedIndices.removeAll()
backgroundLocationsForFlattenedIndices.removeAll()
itemLocationsForFlattenedIndices.removeAll()

var flattenedHeaderIndex = 0
var flattenedFooterIndex = 0
var flattenedBackgroundIndex = 0
var flattenedItemIndex = 0
for sectionIndex in 0..<sectionModels.count {
if sectionModels[sectionIndex].headerModel != nil {
headerLocationsForFlattenedIndices[flattenedHeaderIndex] = ElementLocation(
elementIndex: 0,
sectionIndex: sectionIndex)
flattenedHeaderIndex += 1
}
if MagazineLayout._enableExperimentalOptimizations {
needsPrepareElementLocationsForFlattenedIndices = true
} else {
rebuildElementLocationsForFlattenedIndices()
}
}

if sectionModels[sectionIndex].footerModel != nil {
footerLocationsForFlattenedIndices[flattenedFooterIndex] = ElementLocation(
elementIndex: 0,
sectionIndex: sectionIndex)
flattenedFooterIndex += 1
}
private func prepareElementLocationsForFlattenedIndicesIfNeeded() {
guard needsPrepareElementLocationsForFlattenedIndices else { return }
rebuildElementLocationsForFlattenedIndices()
needsPrepareElementLocationsForFlattenedIndices = false
}

private func rebuildElementLocationsForFlattenedIndices() {
if MagazineLayout._enableExperimentalOptimizations {
newHeaderLocationsForFlattenedIndices.removeAll(keepingCapacity: true)
newFooterLocationsForFlattenedIndices.removeAll(keepingCapacity: true)
newBackgroundLocationsForFlattenedIndices.removeAll(keepingCapacity: true)
newItemLocationsForFlattenedIndices.removeAll(keepingCapacity: true)

for sectionIndex in 0..<sectionModels.count {
if sectionModels[sectionIndex].headerModel != nil {
let elementLocation = ElementLocation(elementIndex: 0, sectionIndex: sectionIndex)
newHeaderLocationsForFlattenedIndices.append(elementLocation)
}

if sectionModels[sectionIndex].footerModel != nil {
let elementLocation = ElementLocation(elementIndex: 0, sectionIndex: sectionIndex)
newFooterLocationsForFlattenedIndices.append(elementLocation)
}

if sectionModels[sectionIndex].backgroundModel != nil {
backgroundLocationsForFlattenedIndices[flattenedBackgroundIndex] = ElementLocation(
elementIndex: 0,
sectionIndex: sectionIndex)
flattenedBackgroundIndex += 1
if sectionModels[sectionIndex].backgroundModel != nil {
let elementLocation = ElementLocation(elementIndex: 0, sectionIndex: sectionIndex)
newBackgroundLocationsForFlattenedIndices.append(elementLocation)
}

for itemIndex in 0..<sectionModels[sectionIndex].numberOfItems {
let elementLocation = ElementLocation(elementIndex: itemIndex, sectionIndex: sectionIndex)
newItemLocationsForFlattenedIndices.append(elementLocation)
}
Comment on lines +656 to +681

@bryankeller bryankeller Jun 9, 2026

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same logic as the existing else branch, but using the new arrays instead of dictionaries

}
} else {
headerLocationsForFlattenedIndices.removeAll()
footerLocationsForFlattenedIndices.removeAll()
backgroundLocationsForFlattenedIndices.removeAll()
itemLocationsForFlattenedIndices.removeAll()

var flattenedHeaderIndex = 0
var flattenedFooterIndex = 0
var flattenedBackgroundIndex = 0
var flattenedItemIndex = 0
for sectionIndex in 0..<sectionModels.count {
if sectionModels[sectionIndex].headerModel != nil {
headerLocationsForFlattenedIndices[flattenedHeaderIndex] = ElementLocation(
elementIndex: 0,
sectionIndex: sectionIndex)
flattenedHeaderIndex += 1
}

if sectionModels[sectionIndex].footerModel != nil {
footerLocationsForFlattenedIndices[flattenedFooterIndex] = ElementLocation(
elementIndex: 0,
sectionIndex: sectionIndex)
flattenedFooterIndex += 1
}

if sectionModels[sectionIndex].backgroundModel != nil {
backgroundLocationsForFlattenedIndices[flattenedBackgroundIndex] = ElementLocation(
elementIndex: 0,
sectionIndex: sectionIndex)
flattenedBackgroundIndex += 1
}

for itemIndex in 0..<sectionModels[sectionIndex].numberOfItems {
itemLocationsForFlattenedIndices[flattenedItemIndex] = ElementLocation(
elementIndex: itemIndex,
sectionIndex: sectionIndex)
flattenedItemIndex += 1
for itemIndex in 0..<sectionModels[sectionIndex].numberOfItems {
itemLocationsForFlattenedIndices[flattenedItemIndex] = ElementLocation(
elementIndex: itemIndex,
sectionIndex: sectionIndex)
flattenedItemIndex += 1
}
Comment on lines +684 to +720

@bryankeller bryankeller Jun 9, 2026

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existing code, just indented and put in an else branch

}
}
}

private func elementLocationFramePairsForElements(
in rect: CGRect,
withElementLocationsForFlattenedIndices elementLocationsForFlattenedIndices: [Int: ElementLocation],
newElementLocationsForFlattenedIndices: [ElementLocation],
andFramesProvidedBy frameProvider: ((ElementLocation) -> CGRect))
-> ElementLocationFramePairs
{
Expand All @@ -650,6 +735,7 @@ final class ModelState {
let indexOfFirstFoundElement = indexOfFirstFoundElement(
in: rect,
withElementLocationsForFlattenedIndices: elementLocationsForFlattenedIndices,
newElementLocationsForFlattenedIndices: newElementLocationsForFlattenedIndices,
andFramesProvidedBy: frameProvider) else
{
return elementLocationFramePairs
Expand All @@ -663,7 +749,8 @@ final class ModelState {
for elementLocationIndex in (0..<indexOfFirstFoundElement).reversed() {
let elementLocation = self.elementLocation(
forFlattenedIndex: elementLocationIndex,
in: elementLocationsForFlattenedIndices)
in: elementLocationsForFlattenedIndices,
newElementLocationsForFlattenedIndices: newElementLocationsForFlattenedIndices)
let frame = frameProvider(elementLocation)

guard frame.maxY > rect.minY else {
Expand All @@ -684,10 +771,17 @@ final class ModelState {
}

// Look forward to find visible elements
for elementLocationIndex in indexOfFirstFoundElement..<elementLocationsForFlattenedIndices.count {
let numberOfElementLocations =
if MagazineLayout._enableExperimentalOptimizations {
newElementLocationsForFlattenedIndices.count
} else {
elementLocationsForFlattenedIndices.count
}
for elementLocationIndex in indexOfFirstFoundElement..<numberOfElementLocations {
let elementLocation = self.elementLocation(
forFlattenedIndex: elementLocationIndex,
in: elementLocationsForFlattenedIndices)
in: elementLocationsForFlattenedIndices,
newElementLocationsForFlattenedIndices: newElementLocationsForFlattenedIndices)
let frame = frameProvider(elementLocation)
guard frame.minY < rect.maxY else { break }

Expand All @@ -701,17 +795,26 @@ final class ModelState {
private func indexOfFirstFoundElement(
in rect: CGRect,
withElementLocationsForFlattenedIndices elementLocationsForFlattenedIndices: [Int: ElementLocation],
newElementLocationsForFlattenedIndices: [ElementLocation],
andFramesProvidedBy frameProvider: ((ElementLocation) -> CGRect))
-> Int?
{
let numberOfElementLocations =
if MagazineLayout._enableExperimentalOptimizations {
newElementLocationsForFlattenedIndices.count
} else {
elementLocationsForFlattenedIndices.count
}

var lowerBound = 0
var upperBound = elementLocationsForFlattenedIndices.count - 1
var upperBound = numberOfElementLocations - 1

while lowerBound <= upperBound {
let index = (lowerBound + upperBound) / 2
let elementLocation = self.elementLocation(
forFlattenedIndex: index,
in: elementLocationsForFlattenedIndices)
in: elementLocationsForFlattenedIndices,
newElementLocationsForFlattenedIndices: newElementLocationsForFlattenedIndices)
let elementFrame = frameProvider(elementLocation)
if elementFrame.maxY <= rect.minY {
lowerBound = index + 1
Expand All @@ -727,14 +830,19 @@ final class ModelState {

private func elementLocation(
forFlattenedIndex index: Int,
in elementLocationsForFlattenedIndices: [Int: ElementLocation])
in elementLocationsForFlattenedIndices: [Int: ElementLocation],
newElementLocationsForFlattenedIndices: [ElementLocation])
-> ElementLocation
{
guard let elementLocation = elementLocationsForFlattenedIndices[index] else {
preconditionFailure("`elementLocationsForFlattenedIndices` must have a complete mapping of indices in 0..<\(elementLocationsForFlattenedIndices.count) to element locations")
}
if MagazineLayout._enableExperimentalOptimizations {
return newElementLocationsForFlattenedIndices[index]
} else {
guard let elementLocation = elementLocationsForFlattenedIndices[index] else {
preconditionFailure("`elementLocationsForFlattenedIndices` must have a complete mapping of indices in 0..<\(elementLocationsForFlattenedIndices.count) to element locations")
}

return elementLocation
return elementLocation
}
}

private func allocateMemoryForSectionMaxYsCache() {
Expand Down Expand Up @@ -770,6 +878,23 @@ final class ModelState {
}

func invalidateSectionMaxYsCacheForSectionIndices(startingAt sectionIndex: Int) {
if MagazineLayout._enableExperimentalOptimizations {
firstInvalidatedSectionMaxYIndex = min(
firstInvalidatedSectionMaxYIndex ?? sectionIndex,
sectionIndex)
} else {
clearSectionMaxYsCache(startingAt: sectionIndex)
}
}

private func flushSectionMaxYsCacheInvalidationIfNeeded() {
guard let firstInvalidatedSectionMaxYIndex else { return }
clearSectionMaxYsCache(startingAt: firstInvalidatedSectionMaxYIndex)
self.firstInvalidatedSectionMaxYIndex = nil
}

/// Clears cached section max-Y values from `sectionIndex` through the end of the cache.
private func clearSectionMaxYsCache(startingAt sectionIndex: Int) {
guard sectionIndex >= 0, sectionIndex < sectionMaxYsCache.count else {
assertionFailure("Cannot invalidate `sectionMaxYsCache` starting at an invalid (negative or out-of-bounds) `sectionIndex` (\(sectionIndex)).")
return
Expand Down
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