Refactor layoutAttributesForElements to fix rare rendering glitches

Blueprints.podspec

@@ -1,7 +1,7 @@
 Pod::Spec.new do |s|
   s.name             = "Blueprints"
   s.summary          = "A collection of flow layouts that is meant to make your life easier."
-  s.version          = "0.11.5"
+  s.version          = "0.12.0"
   s.homepage         = "https://github.com/zenangst/Blueprints"
   s.license          = 'MIT'
   s.author           = { "Christoffer Winterkvist" => "[email protected]" }

Sources/Shared/Core/BlueprintLayout.swift

@@ -338,12 +338,33 @@
     let closure: (LayoutAttributes) -> Bool = scrollDirection == .horizontal
       ? { rect.maxX >= $0.frame.minX }
       : { rect.maxY >= $0.frame.minY }
+    var rect = rect
+    let offset: CGFloat
+
+    // Add offset to the visible rectangle to avoid rare rendering issues when using binary search.
+    // It simply makes the visible rectangle slightly larger to ensure that all items on screen
+    // get rendered correctly. It will use the item size to determine how much offset should be
+    // added as padding to the visible rectangle.
+    switch scrollDirection {
+    case .horizontal:
+      offset = itemSize.width
+      rect.origin.x -= offset
+      rect.size.width += offset * 2
+    case .vertical:
+      offset = itemSize.height
+      rect.origin.y -= offset
+      rect.size.height += offset * 2
+    @unknown default:
+      fatalError("Case not implemented in current implementation")
+    }
+
+    let padding = Int(itemsPerRow ?? 1)
     var items = binarySearch.findElements(in: cachedItemAttributes,
-                                          padding: Int(itemsPerRow ?? 0),
+                                          padding: padding,
                                           less: { closure($0) },
                                           match: { $0.frame.intersects(rect) }) ?? []
     let supplementary = binarySearch.findElements(in: cachedSupplementaryAttributes,
-                                                  padding: Int(itemsPerRow ?? 0),
+                                                  padding: padding,
                                                   less: { closure($0) },
                                                   match: { $0.frame.intersects(rect) }) ?? []
     items.append(contentsOf: supplementary)

Tests/iOS+tvOS/HorizontalBlueprintLayoutTests+iOS+tvOS.swift

@@ -20,9 +20,9 @@ class HorizontalBlueprintLayoutTests_iOS_tvOS: XCTestCase {
     horizontalLayout.prepare()
 
     let size: CGSize = .init(width: 50, height: 50)
-    XCTAssertEqual(horizontalLayout.layoutAttributesForElements(in: CGRect(origin: .init(x: 0, y: 0), size: size))?.count, 1)
-    XCTAssertEqual(horizontalLayout.layoutAttributesForElements(in: CGRect(origin: .init(x: 75, y: 0), size: size))?.count, 2)
-    XCTAssertEqual(horizontalLayout.layoutAttributesForElements(in: CGRect(origin: .init(x: 100, y: 0), size: size))?.count, 1)
+    XCTAssertEqual(horizontalLayout.layoutAttributesForElements(in: CGRect(origin: .init(x: 0, y: 0), size: size))?.count, 2)
+    XCTAssertEqual(horizontalLayout.layoutAttributesForElements(in: CGRect(origin: .init(x: 75, y: 0), size: size))?.count, 4)
+    XCTAssertEqual(horizontalLayout.layoutAttributesForElements(in: CGRect(origin: .init(x: 100, y: 0), size: size))?.count, 3)
     XCTAssertEqual(horizontalLayout.layoutAttributesForElements(in: CGRect(origin: .init(x: 0, y: 0), size: .init(width: 500, height: 500)))?.count, 10)
   }
 }

Tests/iOS+tvOS/VerticalBlueprintLayoutTests+iOS+tvOS.swift

@@ -22,8 +22,8 @@ class VerticalBlueprintLayoutTests_iOS_tvOS: XCTestCase {
     XCTAssertEqual(verticalLayout.layoutAttributesForElements(in: .zero)?.count, 1)
 
     let size = CGSize(width: 50, height: 50)
-    XCTAssertEqual(verticalLayout.layoutAttributesForElements(in: CGRect(origin: .init(x: 0, y: 0), size: size))?.count, 1)
-    XCTAssertEqual(verticalLayout.layoutAttributesForElements(in: CGRect(origin: .init(x: 0, y: 25), size: size))?.count, 2)
+    XCTAssertEqual(verticalLayout.layoutAttributesForElements(in: CGRect(origin: .init(x: 0, y: 0), size: size))?.count, 2)
+    XCTAssertEqual(verticalLayout.layoutAttributesForElements(in: CGRect(origin: .init(x: 0, y: 25), size: size))?.count, 1)
     XCTAssertEqual(verticalLayout.layoutAttributesForElements(in: CGRect(origin: .init(x: 0, y: 50), size: size))?.count, 1)
     XCTAssertEqual(verticalLayout.layoutAttributesForElements(in: CGRect(origin: .init(x: 0, y: 0), size: CGSize(width: 500, height: 500)))?.count, 10)
   }

Tests/macOS/HorizontalBlueprintLayoutTests+macOS.swift

@@ -24,10 +24,10 @@ class HorizontalBlueprintLayoutTests_macOS: XCTestCase {
     XCTAssertEqual(horizontalLayout.layoutAttributesForElements(in: .zero).count, 1)
 
     collectionView.contentOffset = .init(x: 75, y: 0)
-    XCTAssertEqual(horizontalLayout.layoutAttributesForElements(in: collectionView.enclosingScrollView!.documentVisibleRect).count, 2)
+    XCTAssertEqual(horizontalLayout.layoutAttributesForElements(in: collectionView.enclosingScrollView!.documentVisibleRect).count, 4)
 
     collectionView.contentOffset = .init(x: 100, y: 0)
-    XCTAssertEqual(horizontalLayout.layoutAttributesForElements(in: collectionView.enclosingScrollView!.documentVisibleRect).count, 1)
+    XCTAssertEqual(horizontalLayout.layoutAttributesForElements(in: collectionView.enclosingScrollView!.documentVisibleRect).count, 3)
 
     collectionView.enclosingScrollView?.frame.size = CGSize(width: 500, height: 500)
     collectionView.contentOffset = .init(x: 0, y: 0)

Tests/macOS/VerticalBlueprintLayoutTests+macOS.swift

@@ -21,10 +21,10 @@ class VerticalBlueprintLayoutTests_macOS: XCTestCase {
 
     collectionView.enclosingScrollView?.frame.size = .init(width: 50, height: 50)
     collectionView.contentOffset = .init(x: 0, y: 0)
-    XCTAssertEqual(verticalLayout.layoutAttributesForElements(in: collectionView.enclosingScrollView!.documentVisibleRect).count, 1)
+    XCTAssertEqual(verticalLayout.layoutAttributesForElements(in: collectionView.enclosingScrollView!.documentVisibleRect).count, 2)
 
     collectionView.contentOffset = .init(x: 0, y: 25)
-    XCTAssertEqual(verticalLayout.layoutAttributesForElements(in: collectionView.enclosingScrollView!.documentVisibleRect).count, 2)
+    XCTAssertEqual(verticalLayout.layoutAttributesForElements(in: collectionView.enclosingScrollView!.documentVisibleRect).count, 1)
 
     collectionView.contentOffset = .init(x: 0, y: 50)
     XCTAssertEqual(verticalLayout.layoutAttributesForElements(in: collectionView.enclosingScrollView!.documentVisibleRect).count, 1)