[ASTextNode] Optimize handling of constrained size to almost never recreate NSLayoutManager

This also fixes two fairly subtle but serious bugs, #1076 and #1046.

AsyncDisplayKit/TextKit/ASTextKitContext.h

@@ -30,6 +30,8 @@
                          constrainedSize:(CGSize)constrainedSize
                     layoutManagerFactory:(NSLayoutManager*(*)(void))layoutManagerFactory;
 
+@property (nonatomic, assign, readwrite) CGSize constrainedSize;
+
 /**
  All operations on TextKit values MUST occur within this locked context.  Simultaneous access (even non-mutative) to
  TextKit components may cause crashes.

AsyncDisplayKit/TextKit/ASTextKitContext.mm

@@ -49,6 +49,16 @@
   return self;
 }
 
+- (CGSize)constrainedSize
+{
+  return _textContainer.size;
+}
+
+- (void)setConstrainedSize:(CGSize)constrainedSize
+{
+  _textContainer.size = constrainedSize;
+}
+
 - (void)performBlockWithLockedTextKitComponents:(void (^)(NSLayoutManager *,
                                                           NSTextStorage *,
                                                           NSTextContainer *))block

AsyncDisplayKit/TextKit/ASTextKitRenderer.h

@@ -37,7 +37,6 @@
 
 /**
  Designated Initializer
-dvlkferufedgjnhjjfhldjedlunvtdtv
  @discussion Sizing will occur as a result of initialization, so be careful when/where you use this.
  */
 - (instancetype)initWithTextKitAttributes:(const ASTextKitAttributes &)textComponentAttributes
@@ -51,7 +50,7 @@ dvlkferufedgjnhjjfhldjedlunvtdtv
 
 @property (nonatomic, assign, readonly) ASTextKitAttributes attributes;
 
-@property (nonatomic, assign, readonly) CGSize constrainedSize;
+@property (nonatomic, assign, readwrite) CGSize constrainedSize;
 
 #pragma mark - Drawing
 /*

AsyncDisplayKit/TextKit/ASTextKitRenderer.mm

@@ -17,6 +17,9 @@
 #import "ASTextKitTailTruncater.h"
 #import "ASTextKitTruncating.h"
 
+//#define LOG(...) NSLog(__VA_ARGS__)
+#define LOG(...)
+
 static NSCharacterSet *_defaultAvoidTruncationCharacterSet()
 {
   static NSCharacterSet *truncationCharacterSet;
@@ -65,12 +68,10 @@ static NSCharacterSet *_defaultAvoidTruncationCharacterSet()
 {
   if (!_truncater) {
     ASTextKitAttributes attributes = _attributes;
-    // We must inset the constrained size by the size of the shadower.
-    CGSize shadowConstrainedSize = [[self shadower] insetSizeWithConstrainedSize:_constrainedSize];
+    NSCharacterSet *avoidTailTruncationSet = attributes.avoidTailTruncationSet ? : _defaultAvoidTruncationCharacterSet();
     _truncater = [[ASTextKitTailTruncater alloc] initWithContext:[self context]
                                       truncationAttributedString:attributes.truncationAttributedString
-                                          avoidTailTruncationSet:attributes.avoidTailTruncationSet ?: _defaultAvoidTruncationCharacterSet()
-                                                 constrainedSize:shadowConstrainedSize];
+                                          avoidTailTruncationSet:avoidTailTruncationSet];
   }
   return _truncater;
 }
@@ -79,6 +80,7 @@ static NSCharacterSet *_defaultAvoidTruncationCharacterSet()
 {
   if (!_context) {
     ASTextKitAttributes attributes = _attributes;
+    // We must inset the constrained size by the size of the shadower.
     CGSize shadowConstrainedSize = [[self shadower] insetSizeWithConstrainedSize:_constrainedSize];
     _context = [[ASTextKitContext alloc] initWithAttributedString:attributes.attributedString
                                                     lineBreakMode:attributes.lineBreakMode
@@ -92,6 +94,30 @@ static NSCharacterSet *_defaultAvoidTruncationCharacterSet()
 
 #pragma mark - Sizing
 
+- (CGSize)size
+{
+  if (!_sizeIsCalculated) {
+    [self _calculateSize];
+    _sizeIsCalculated = YES;
+  }
+  return _calculatedSize;
+}
+
+- (void)setConstrainedSize:(CGSize)constrainedSize
+{
+  if (!CGSizeEqualToSize(constrainedSize, _constrainedSize)) {
+    _sizeIsCalculated = NO;
+    _constrainedSize = constrainedSize;
+    // If the context isn't created yet, it will be initialized with the appropriate size when next accessed.
+    if (_context) {
+      // If we're updating an existing context, make sure to use the same inset logic used during initialization.
+      // This codepath allows us to reuse the
+      CGSize shadowConstrainedSize = [[self shadower] insetSizeWithConstrainedSize:constrainedSize];
+      _context.constrainedSize = shadowConstrainedSize;
+    }
+  }
+}
+
 - (void)_calculateSize
 {
   // Force glyph generation and layout, which may not have happened yet (and isn't triggered by
@@ -111,16 +137,7 @@ static NSCharacterSet *_defaultAvoidTruncationCharacterSet()
   // to make sure our width calculations aren't being offset by glyphs going beyond the constrained rect.
   boundingRect = CGRectIntersection(boundingRect, {.size = constrainedRect.size});
 
-  _calculatedSize = [_shadower outsetSizeWithInsetSize:CGSizeMake(boundingRect.size.width + boundingRect.origin.x, boundingRect.size.height + boundingRect.origin.y)];
-}
-
-- (CGSize)size
-{
-  if (!_sizeIsCalculated) {
-    [self _calculateSize];
-    _sizeIsCalculated = YES;
-  }
-  return _calculatedSize;
+  _calculatedSize = [_shadower outsetSizeWithInsetSize:boundingRect.size];
 }
 
 #pragma mark - Drawing
@@ -136,8 +153,12 @@ static NSCharacterSet *_defaultAvoidTruncationCharacterSet()
   [[self shadower] setShadowInContext:context];
   UIGraphicsPushContext(context);
 
+  LOG(@"%@, shadowInsetBounds = %@",self, NSStringFromCGRect(shadowInsetBounds));
+  
   [[self context] performBlockWithLockedTextKitComponents:^(NSLayoutManager *layoutManager, NSTextStorage *textStorage, NSTextContainer *textContainer) {
+    LOG(@"usedRect: %@", NSStringFromCGRect([layoutManager usedRectForTextContainer:textContainer]));
     NSRange glyphRange = [layoutManager glyphRangeForTextContainer:textContainer];
+    LOG(@"boundingRect: %@", NSStringFromCGRect([layoutManager boundingRectForGlyphRange:glyphRange inTextContainer:textContainer]));
     [layoutManager drawBackgroundForGlyphRange:glyphRange atPoint:shadowInsetBounds.origin];
     [layoutManager drawGlyphsForGlyphRange:glyphRange atPoint:shadowInsetBounds.origin];
   }];

AsyncDisplayKit/TextKit/ASTextKitTailTruncater.mm

@@ -18,7 +18,6 @@
   __weak ASTextKitContext *_context;
   NSAttributedString *_truncationAttributedString;
   NSCharacterSet *_avoidTailTruncationSet;
-  CGSize _constrainedSize;
 }
 @synthesize visibleRanges = _visibleRanges;
 @synthesize truncationStringRect = _truncationStringRect;
@@ -26,13 +25,11 @@
 - (instancetype)initWithContext:(ASTextKitContext *)context
      truncationAttributedString:(NSAttributedString *)truncationAttributedString
          avoidTailTruncationSet:(NSCharacterSet *)avoidTailTruncationSet
-                constrainedSize:(CGSize)constrainedSize
 {
   if (self = [super init]) {
     _context = context;
     _truncationAttributedString = truncationAttributedString;
     _avoidTailTruncationSet = avoidTailTruncationSet;
-    _constrainedSize = constrainedSize;
 
     [self _truncate];
   }

AsyncDisplayKit/TextKit/ASTextKitTruncating.h

@@ -31,7 +31,6 @@
  */
 - (instancetype)initWithContext:(ASTextKitContext *)context
      truncationAttributedString:(NSAttributedString *)truncationAttributedString
-         avoidTailTruncationSet:(NSCharacterSet *)avoidTailTruncationSet
-                constrainedSize:(CGSize)constrainedSize;
+         avoidTailTruncationSet:(NSCharacterSet *)avoidTailTruncationSet;
 
 @end