Return attributes for items that intersect

Headers/AppKit/NSCollectionView.h

@@ -438,9 +438,9 @@ APPKIT_EXPORT_CLASS
 
   // Managing items
   NSMutableArray *_visibleItems;
-  NSSet *_indexPathsForVisibleItems;
+  NSMutableSet *_indexPathsForVisibleItems;
   NSDictionary *_visibleSupplementaryViews;
-  NSSet *_indexPathsForSupplementaryElementsOfKind;
+  NSMutableSet *_indexPathsForSupplementaryElementsOfKind;
 
   // Registered class/nib for item identifier
   NSMapTable *_registeredNibs;

Source/NSCollectionView.m

@@ -1391,6 +1391,7 @@ static NSString *placeholderItem = nil;
       NSView *v = [item view];
 
       [_visibleItems addObject: item];
+      [_indexPathsForVisibleItems addObject: path];
       if (_collectionViewLayout)
         {
           NSCollectionViewLayoutAttributes *attrs =
@@ -1449,6 +1450,7 @@ static NSString *placeholderItem = nil;
 
   [self setFrame: newRect];
   [_visibleItems removeAllObjects];
+  [_indexPathsForVisibleItems removeAllObjects];
   [self setSubviews: [NSArray array]];
   [_collectionViewLayout prepareLayout];
   for (cs = 0; cs < ns; cs++)

Source/NSCollectionViewFlowLayout.m

@@ -372,11 +372,6 @@
   _dr = 0;
 }
 
-- (NSArray *) layoutAttributesForElementsInRect: (NSRect)rect
-{
-  return nil;
-}
-
 - (NSCollectionViewLayoutAttributes *) layoutAttributesForItemAtIndexPath: (NSIndexPath *)indexPath
 {
   NSCollectionViewLayoutAttributes *attrs = AUTORELEASE([[NSCollectionViewLayoutAttributes alloc] init]);

Source/NSCollectionViewLayout.m

@@ -23,6 +23,27 @@
 */
 
 #import "AppKit/NSCollectionViewLayout.h"
+#import "AppKit/NSCollectionViewItem.h"
+
+#import "GSFastEnumeration.h"
+
+@interface NSCollectionViewItem (__NSCollectionViewLayout__)
+- (NSCollectionViewLayoutAttributes *) attrs;
+@end
+
+@implementation NSCollectionViewItem (__NSCollectionViewLayout__)  
+- (NSCollectionViewLayoutAttributes *) attrs
+{
+  NSCollectionViewLayoutAttributes *attrs = AUTORELEASE([[NSCollectionViewLayoutAttributes alloc] init]);
+
+  [attrs setFrame: [[self view] frame]];
+  [attrs setSize: [[self view] frame].size];
+  [attrs setAlpha: [[self view] alphaValue]];
+  [attrs setHidden: [[self view] isHidden]];
+
+  return attrs;
+}
+@end
 
 @implementation NSCollectionViewLayoutAttributes
 
@@ -287,7 +308,24 @@
 
 - (NSArray *) layoutAttributesForElementsInRect: (NSRect)rect
 {
-  return nil;
+  NSMutableArray *result = [NSMutableArray array];
+  NSArray *items = [_collectionView visibleItems];
+  
+  FOR_IN(NSCollectionViewItem*, i, items)
+    {
+      NSView *v = [i view];
+      NSRect f = [v frame];
+      BOOL intersects = NSIntersectsRect(f, rect);
+    
+      if (intersects)
+        {
+          NSCollectionViewLayoutAttributes *a = [i attrs];
+          [result addObject: a]; // add item since it intersects
+        }
+    }
+  END_FOR_IN(items);
+
+  return result;
 }
 
 - (NSCollectionViewLayoutAttributes *) layoutAttributesForItemAtIndexPath: (NSIndexPath *)indexPath