[Yoga] Add insertYogaNode:atIndex: method. Improve handling of relayouts. (#469)

* [Yoga] Add insertYogaNode:atIndex: method. Improve handling of relayouts.

* Add new "version" parameter to Yoga initialization of ASDisplayNodeLayout C++ struct.

CHANGELOG.md

@@ -1,6 +1,7 @@
 ## master
 
 * Add your own contributions to the next release on the line below this with your name.
+- [Yoga] Add insertYogaNode:atIndex: method. Improve handling of relayouts. [Scott Goodson](https://github.com/appleguy)
 - [ASCollectionNode] Add -isProcessingUpdates and -onDidFinishProcessingUpdates: APIs. [#522](https://github.com/TextureGroup/Texture/pull/522) [Scott Goodson](https://github.com/appleguy)
 - [Accessibility] Add .isAccessibilityContainer property, allowing automatic aggregation of children's a11y labels. [#468][Scott Goodson](https://github.com/appleguy)
 - [ASImageNode] Enabled .clipsToBounds by default, fixing the use of .cornerRadius and clipping of GIFs. [Scott Goodson](https://github.com/appleguy) [#466](https://github.com/TextureGroup/Texture/pull/466)

Source/ASDisplayNode+Beta.h

@@ -175,12 +175,15 @@ extern void ASDisplayNodePerformBlockOnEveryYogaChild(ASDisplayNode * _Nullable
 
 - (void)addYogaChild:(ASDisplayNode *)child;
 - (void)removeYogaChild:(ASDisplayNode *)child;
+- (void)insertYogaChild:(ASDisplayNode *)child atIndex:(NSUInteger)index;
 
 - (void)semanticContentAttributeDidChange:(UISemanticContentAttribute)attribute;
 
 @property (nonatomic, assign) BOOL yogaLayoutInProgress;
 @property (nonatomic, strong, nullable) ASLayout *yogaCalculatedLayout;
-// These methods should not normally be called directly.
+
+// These methods are intended to be used internally to Texture, and should not be called directly.
+- (BOOL)shouldHaveYogaMeasureFunc;
 - (void)invalidateCalculatedYogaLayout;
 - (void)calculateLayoutFromYogaRoot:(ASSizeRange)rootConstrainedSize;
 

Source/ASDisplayNode+Yoga.mm

@@ -59,20 +59,7 @@
 
 - (void)addYogaChild:(ASDisplayNode *)child
 {
-  if (child == nil) {
-    return;
-  }
-  if (_yogaChildren == nil) {
-    _yogaChildren = [NSMutableArray array];
-  }
-
-  // Clean up state in case this child had another parent.
-  [self removeYogaChild:child];
-
-  [_yogaChildren addObject:child];
-
-  // YGNodeRef insertion is done in setParent:
-  child.yogaParent = self;
+  [self insertYogaChild:child atIndex:_yogaChildren.count];
 }
 
 - (void)removeYogaChild:(ASDisplayNode *)child
@@ -87,6 +74,24 @@
   child.yogaParent = nil;
 }
 
+- (void)insertYogaChild:(ASDisplayNode *)child atIndex:(NSUInteger)index
+{
+  if (child == nil) {
+    return;
+  }
+  if (_yogaChildren == nil) {
+    _yogaChildren = [NSMutableArray array];
+  }
+
+  // Clean up state in case this child had another parent.
+  [self removeYogaChild:child];
+
+  [_yogaChildren insertObject:child atIndex:index];
+
+  // YGNodeRef insertion is done in setParent:
+  child.yogaParent = self;
+}
+
 - (void)semanticContentAttributeDidChange:(UISemanticContentAttribute)attribute
 {
   if (AS_AT_LEAST_IOS9) {
@@ -168,28 +173,72 @@
   CGSize size = CGSizeMake(YGNodeLayoutGetWidth(yogaNode), YGNodeLayoutGetHeight(yogaNode));
   ASLayout *layout = [ASLayout layoutWithLayoutElement:self size:size sublayouts:sublayouts];
 
+#if ASDISPLAYNODE_ASSERTIONS_ENABLED
+  // Assert that the sublayout is already flattened.
+  for (ASLayout *sublayout in layout.sublayouts) {
+    if (sublayout.sublayouts.count > 0 || ASDynamicCast(sublayout.layoutElement, ASDisplayNode) == nil) {
+      ASDisplayNodeAssert(NO, @"Yoga sublayout is not flattened! %@, %@", self, sublayout);
+    }
+  }
+#endif
+
+  // Because this layout won't go through the rest of the logic in calculateLayoutThatFits:, flatten it now.
+  layout = [layout filteredNodeLayoutTree];
+
+  if ([self.yogaCalculatedLayout isEqual:layout] == NO) {
     self.yogaCalculatedLayout = layout;
+  } else {
+    layout = self.yogaCalculatedLayout;
+    ASYogaLog("-setupYogaCalculatedLayout: applying identical ASLayout: %@", layout);
+  }
+
+  // Setup _pendingDisplayNodeLayout to reference the Yoga-calculated ASLayout, *unless* we are a leaf node.
+  // Leaf yoga nodes may have their own .sublayouts, if they use a layout spec (such as ASButtonNode).
+  // Their _pending variable is set after passing the Yoga checks at the start of -calculateLayoutThatFits:
+
+  // For other Yoga nodes, there is no code that will set _pending unless we do it here. Why does it need to be set?
+  // When CALayer triggers the -[ASDisplayNode __layout] call, we will check if our current _pending layout
+  // has a size which matches our current bounds size. If it does, that layout will be used without recomputing it.
+
+  // NOTE: Yoga does not make the constrainedSize available to intermediate nodes in the tree (e.g. not root or leaves).
+  // Although the size range provided here is not accurate, this will only affect caching of calls to layoutThatFits:
+  // These calls will behave as if they are not cached, starting a new Yoga layout pass, but this will tap into Yoga's
+  // own internal cache.
+
+  if ([self shouldHaveYogaMeasureFunc] == NO) {
+    YGNodeRef parentNode = YGNodeGetParent(yogaNode);
+    CGSize parentSize = CGSizeZero;
+    if (parentNode) {
+      parentSize.width = YGNodeLayoutGetWidth(parentNode);
+      parentSize.height = YGNodeLayoutGetHeight(parentNode);
+    }
+    _pendingDisplayNodeLayout = std::make_shared<ASDisplayNodeLayout>(layout, ASSizeRangeUnconstrained, parentSize, 0);
+  }
 }
 
-- (void)updateYogaMeasureFuncIfNeeded
+- (BOOL)shouldHaveYogaMeasureFunc
 {
   // Size calculation via calculateSizeThatFits: or layoutSpecThatFits:
   // This will be used for ASTextNode, as well as any other node that has no Yoga children
   BOOL isLeafNode = (self.yogaChildren.count == 0);
   BOOL definesCustomLayout = [self implementsLayoutMethod];
+  return (isLeafNode && definesCustomLayout);
+}
 
+- (void)updateYogaMeasureFuncIfNeeded
+{
   // We set the measure func only during layout. Otherwise, a cycle is created:
   // The YGNodeRef Context will retain the ASDisplayNode, which retains the style, which owns the YGNodeRef.
-  BOOL shouldHaveMeasureFunc = (isLeafNode && definesCustomLayout && checkFlag(YogaLayoutInProgress));
+  BOOL shouldHaveMeasureFunc = ([self shouldHaveYogaMeasureFunc] && checkFlag(YogaLayoutInProgress));
 
   ASLayoutElementYogaUpdateMeasureFunc(self.style.yogaNode, shouldHaveMeasureFunc ? self : nil);
 }
 
 - (void)invalidateCalculatedYogaLayout
 {
-  // Yoga internally asserts that this method may only be called on nodes with a measurement function.
   YGNodeRef yogaNode = self.style.yogaNode;
   if (yogaNode && YGNodeGetMeasureFunc(yogaNode)) {
+    // Yoga internally asserts that MarkDirty() may only be called on nodes with a measurement function.
     YGNodeMarkDirty(yogaNode);
   }
   self.yogaCalculatedLayout = nil;
@@ -200,7 +249,7 @@
   ASDisplayNode *yogaParent = self.yogaParent;
 
   if (yogaParent) {
-    ASYogaLog(@"ESCALATING to Yoga root: %@", self);
+    ASYogaLog("ESCALATING to Yoga root: %@", self);
     // TODO(appleguy): Consider how to get the constrainedSize for the yogaRoot when escalating manually.
     [yogaParent calculateLayoutFromYogaRoot:ASSizeRangeUnconstrained];
     return;
@@ -217,7 +266,7 @@
     rootConstrainedSize = [self _locked_constrainedSizeForLayoutPass];
   }
 
-  ASYogaLog(@"CALCULATING at Yoga root with constraint = {%@, %@}: %@",
+  ASYogaLog("CALCULATING at Yoga root with constraint = {%@, %@}: %@",
             NSStringFromCGSize(rootConstrainedSize.min), NSStringFromCGSize(rootConstrainedSize.max), self);
 
   YGNodeRef rootYogaNode = self.style.yogaNode;

Source/ASDisplayNode.mm

@@ -967,23 +967,30 @@ static ASDisplayNodeMethodOverrides GetASDisplayNodeMethodOverrides(Class c)
   // - This node is a Yoga tree root: it has no yogaParent, but has yogaChildren.
   // - This node is a Yoga tree node: it has both a yogaParent and yogaChildren.
   // - This node is a Yoga tree leaf: it has a yogaParent, but no yogaChidlren.
-  // If we're a leaf node, we are probably being called by a measure function and proceed as normal.
-  // If we're a yoga root or tree node, initiate a new Yoga calculation pass from root.
   YGNodeRef yogaNode = _style.yogaNode;
   BOOL hasYogaParent = (_yogaParent != nil);
   BOOL hasYogaChildren = (_yogaChildren.count > 0);
   BOOL usesYoga = (yogaNode != NULL && (hasYogaParent || hasYogaChildren));
-  if (usesYoga && (_yogaParent == nil || _yogaChildren.count > 0)) {
+  if (usesYoga) {
     // This node has some connection to a Yoga tree.
+    if ([self shouldHaveYogaMeasureFunc] == NO) {
+      // If we're a yoga root, tree node, or leaf with no measure func (e.g. spacer), then
+      // initiate a new Yoga calculation pass from root.
       ASDN::MutexUnlocker ul(__instanceLock__);
-
+      as_activity_create_for_scope("Yoga layout calculation");
       if (self.yogaLayoutInProgress == NO) {
+        ASYogaLog("Calculating yoga layout from root %@, %@", self, NSStringFromASSizeRange(constrainedSize));
         [self calculateLayoutFromYogaRoot:constrainedSize];
+      } else {
+        ASYogaLog("Reusing existing yoga layout %@", _yogaCalculatedLayout);
       }
       ASDisplayNodeAssert(_yogaCalculatedLayout, @"Yoga node should have a non-nil layout at this stage: %@", self);
       return _yogaCalculatedLayout;
+    } else {
+      // If we're a yoga leaf node with custom measurement function, proceed with normal layout so layoutSpecs can run (e.g. ASButtonNode).
+      ASYogaLog("PROCEEDING past Yoga check to calculate ASLayout for: %@", self);
+    }
   }
-  ASYogaLog(@"PROCEEDING past Yoga check to calculate ASLayout for: %@", self);
 #endif /* YOGA */
   
   // Manual size calculation via calculateSizeThatFits:

Source/Layout/ASLayout.mm

@@ -271,6 +271,27 @@ static std::atomic_bool static_retainsSublayoutLayoutElements = ATOMIC_VAR_INIT(
   return layout;
 }
 
+#pragma mark - Equality Checking
+
+- (BOOL)isEqual:(id)object
+{
+  ASLayout *layout = ASDynamicCast(object, ASLayout);
+  if (layout == nil) {
+    return NO;
+  }
+
+  if (!CGSizeEqualToSize(_size, layout.size)) return NO;
+  if (!CGPointEqualToPoint(_position, layout.position)) return NO;
+  if (_layoutElement != layout.layoutElement) return NO;
+
+  NSArray *sublayouts = layout.sublayouts;
+  if (sublayouts != _sublayouts && (sublayouts == nil || _sublayouts == nil || ![_sublayouts isEqual:sublayouts])) {
+    return NO;
+  }
+
+  return YES;
+}
+
 #pragma mark - Accessors
 
 - (ASLayoutElementType)type

Source/Layout/ASYogaUtilities.h

@@ -15,9 +15,11 @@
 #if YOGA /* YOGA */
 
 #import <AsyncDisplayKit/ASLayout.h>
+#import <AsyncDisplayKit/ASLog.h>
 #import <AsyncDisplayKit/ASDisplayNode+Beta.h>
 
-#define ASYogaLog(...) //NSLog(__VA_ARGS__)
+// Should pass a string literal, not an NSString as the first argument to ASYogaLog
+#define ASYogaLog(x, ...) as_log_verbose(ASLayoutLog(), x, ##__VA_ARGS__);
 
 @interface ASDisplayNode (YogaHelpers)