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Refine top and bottom item anchor calculation #129

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merged 2 commits into from
May 2, 2024
Merged

Refine top and bottom item anchor calculation #129

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901afc8
Refine top and bottom item anchor calculation
bryankeller May 2, 2024
6e2f69f
Fix build
bryankeller May 2, 2024
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68 changes: 14 additions & 54 deletions MagazineLayout/LayoutCore/Types/TargetContentOffsetAnchor.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -22,8 +22,8 @@ import UIKit
enum TargetContentOffsetAnchor: Equatable {
case top
case bottom
case topItem(id: String, itemEdge: ItemEdge, distanceFromTop: CGFloat)
case bottomItem(id: String, itemEdge: ItemEdge, distanceFromBottom: CGFloat)
case topItem(id: String, distanceFromTop: CGFloat)
case bottomItem(id: String, distanceFromBottom: CGFloat)

static func targetContentOffsetAnchor(
verticalLayoutDirection: MagazineLayoutVerticalLayoutDirection,
Expand Down Expand Up @@ -65,37 +65,19 @@ enum TargetContentOffsetAnchor: Equatable {
return .top
case .inMiddle, .atBottom:
let top = bounds.minY + topInset
let topDistanceFromTop = firstVisibleItemFrame.value(for: .top) - top
let bottomDistanceFromTop = firstVisibleItemFrame.value(for: .bottom) - top
if abs(topDistanceFromTop) < abs(bottomDistanceFromTop) {
return .topItem(
id: firstVisibleItemID,
itemEdge: .top,
distanceFromTop: topDistanceFromTop.alignedToPixel(forScreenWithScale: scale))
} else {
return .topItem(
id: firstVisibleItemID,
itemEdge: .bottom,
distanceFromTop: bottomDistanceFromTop.alignedToPixel(forScreenWithScale: scale))
}
let distanceFromTop = firstVisibleItemFrame.minY - top
return .topItem(
id: firstVisibleItemID,
distanceFromTop: distanceFromTop.alignedToPixel(forScreenWithScale: scale))
}
case .bottomToTop:
switch position {
case .atTop, .inMiddle:
let bottom = bounds.maxY - bottomInset
let topDistanceFromBottom = lastVisibleItemFrame.value(for: .top) - bottom
let bottomDistanceFromBottom = lastVisibleItemFrame.value(for: .bottom) - bottom
if abs(topDistanceFromBottom) < abs(bottomDistanceFromBottom) {
return .bottomItem(
id: lastVisibleItemID,
itemEdge: .top,
distanceFromBottom: topDistanceFromBottom.alignedToPixel(forScreenWithScale: scale))
} else {
return .bottomItem(
id: lastVisibleItemID,
itemEdge: .bottom,
distanceFromBottom: bottomDistanceFromBottom.alignedToPixel(forScreenWithScale: scale))
}
let distanceFromBottom = lastVisibleItemFrame.maxY - bottom
return .bottomItem(
id: lastVisibleItemID,
distanceFromBottom: distanceFromBottom.alignedToPixel(forScreenWithScale: scale))
case .atBottom:
return .bottom
}
Expand All @@ -121,44 +103,22 @@ enum TargetContentOffsetAnchor: Equatable {
case .bottom:
return maxYOffset

case .topItem(let id, let itemEdge, let distanceFromTop):
case .topItem(let id, let distanceFromTop):
guard let indexPath = indexPathForItemID(id) else { return bounds.minY }
let itemFrame = frameForItemAtIndexPath(indexPath)
let proposedYOffset = itemFrame.value(for: itemEdge) - topInset - distanceFromTop
let proposedYOffset = itemFrame.minY - topInset - distanceFromTop
return min(max(proposedYOffset, minYOffset), maxYOffset) // Clamp between minYOffset...maxYOffset

case .bottomItem(let id, let itemEdge, let distanceFromBottom):
case .bottomItem(let id, let distanceFromBottom):
guard let indexPath = indexPathForItemID(id) else { return bounds.minY }
let itemFrame = frameForItemAtIndexPath(indexPath)
let proposedYOffset = itemFrame.value(for: itemEdge) - bounds.height + bottomInset - distanceFromBottom
let proposedYOffset = itemFrame.maxY - bounds.height + bottomInset - distanceFromBottom
return min(max(proposedYOffset, minYOffset), maxYOffset) // Clamp between minYOffset...maxYOffset
}
}

}

// MARK: ItemEdge

enum ItemEdge {
case top
case bottom
}

// MARK: CGRect + Item Edge Value

private extension CGRect {

func value(for itemEdge: ItemEdge) -> CGFloat {
switch itemEdge {
case .top:
return minY
case .bottom:
return maxY
}
}

}

// MARK: - Position

private enum Position {
Expand Down
3 changes: 1 addition & 2 deletions MagazineLayout/Public/MagazineLayout.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -1261,9 +1261,8 @@ public final class MagazineLayout: UICollectionViewLayout {
bottomInset: CGFloat)
-> TargetContentOffsetAnchor?
{
let insetBounds = bounds.inset(by: .init(top: topInset, left: 0, bottom: bottomInset, right: 0))
var visibleItemLocationFramePairs = [ElementLocationFramePair]()
for itemLocationFramePair in modelState.itemLocationFramePairs(forItemsIn: insetBounds) {
for itemLocationFramePair in modelState.itemLocationFramePairs(forItemsIn: bounds) {
visibleItemLocationFramePairs.append(itemLocationFramePair)
}
visibleItemLocationFramePairs.sort { $0.elementLocation < $1.elementLocation }
Expand Down
16 changes: 8 additions & 8 deletions Tests/TargetContentOffsetAnchorTests.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -48,7 +48,7 @@ final class TargetContentOffsetAnchorTests: XCTestCase {
lastVisibleItemID: "6",
firstVisibleItemFrame: CGRect(x: 0, y: 560, width: 300, height: 20),
lastVisibleItemFrame: CGRect(x: 0, y: 800, width: 300, height: 20))
XCTAssert(anchor == .topItem(id: "2", itemEdge: .top, distanceFromTop: 10))
XCTAssert(anchor == .topItem(id: "2", distanceFromTop: 10))
}

func testAnchor_TopToBottom_ScrolledToBottom() throws {
Expand All @@ -63,7 +63,7 @@ final class TargetContentOffsetAnchorTests: XCTestCase {
lastVisibleItemID: "10",
firstVisibleItemFrame: CGRect(x: 0, y: 1700, width: 300, height: 20),
lastVisibleItemFrame: CGRect(x: 0, y: 1950, width: 300, height: 20))
XCTAssert(anchor == .topItem(id: "6", itemEdge: .top, distanceFromTop: 20))
XCTAssert(anchor == .topItem(id: "6", distanceFromTop: 20))
}

func testAnchor_TopToBottom_SmallContentHeight() throws {
Expand Down Expand Up @@ -95,7 +95,7 @@ final class TargetContentOffsetAnchorTests: XCTestCase {
lastVisibleItemID: "4",
firstVisibleItemFrame: CGRect(x: 0, y: 0, width: 300, height: 20),
lastVisibleItemFrame: CGRect(x: 0, y: 290, width: 300, height: 20))
XCTAssert(anchor == .bottomItem(id: "4", itemEdge: .bottom, distanceFromBottom: -10))
XCTAssert(anchor == .bottomItem(id: "4", distanceFromBottom: -10))
}

func testAnchor_BottomToTop_ScrolledToMiddle() throws {
Expand All @@ -110,7 +110,7 @@ final class TargetContentOffsetAnchorTests: XCTestCase {
lastVisibleItemID: "6",
firstVisibleItemFrame: CGRect(x: 0, y: 560, width: 300, height: 20),
lastVisibleItemFrame: CGRect(x: 0, y: 800, width: 300, height: 20))
XCTAssert(anchor == .bottomItem(id: "6", itemEdge: .bottom, distanceFromBottom: -50))
XCTAssert(anchor == .bottomItem(id: "6", distanceFromBottom: -50))
}

func testAnchor_BottomToTop_ScrolledToBottom() throws {
Expand Down Expand Up @@ -158,7 +158,7 @@ final class TargetContentOffsetAnchorTests: XCTestCase {
}

func testOffset_TopToBottom_ScrolledToMiddle() {
let anchor = TargetContentOffsetAnchor.topItem(id: "2", itemEdge: .top, distanceFromTop: 10)
let anchor = TargetContentOffsetAnchor.topItem(id: "2", distanceFromTop: 10)
let offset = anchor.yOffset(
topInset: 50,
bottomInset: 30,
Expand All @@ -170,7 +170,7 @@ final class TargetContentOffsetAnchorTests: XCTestCase {
}

func testOffset_TopToBottom_ScrolledToBottom() {
let anchor = TargetContentOffsetAnchor.topItem(id: "2", itemEdge: .top, distanceFromTop: 10)
let anchor = TargetContentOffsetAnchor.topItem(id: "2", distanceFromTop: 10)
let offset = anchor.yOffset(
topInset: 50,
bottomInset: 30,
Expand All @@ -184,7 +184,7 @@ final class TargetContentOffsetAnchorTests: XCTestCase {
// MARK: Bottom-to-Top Target Content Offset Tests

func testOffset_BottomToTop_ScrolledToTop() {
let anchor = TargetContentOffsetAnchor.bottomItem(id: "4", itemEdge: .bottom, distanceFromBottom: -10)
let anchor = TargetContentOffsetAnchor.bottomItem(id: "4", distanceFromBottom: -10)
let offset = anchor.yOffset(
topInset: 50,
bottomInset: 30,
Expand All @@ -196,7 +196,7 @@ final class TargetContentOffsetAnchorTests: XCTestCase {
}

func testOffset_BottomToTop_ScrolledToMiddle() {
let anchor = TargetContentOffsetAnchor.bottomItem(id: "6", itemEdge: .bottom, distanceFromBottom: -50)
let anchor = TargetContentOffsetAnchor.bottomItem(id: "6", distanceFromBottom: -50)
let offset = anchor.yOffset(
topInset: 50,
bottomInset: 30,
Expand Down
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