Switch to instance methods of draw and display

This patch switches to instance methods of draw and display for
ASTextNode and ASImageNode to attempt to increase their performance.

It also fixes some thread safety issues in ASImageNode which appear
to have been regressions (though probably not hit very often).

And it sets up work for allowing modification of CGContexts before
and after a node's contents are drawn.

AsyncDisplayKit/ASTextNode.mm

@@ -34,13 +34,7 @@ static NSString *ASTextNodeTruncationTokenAttributeName = @"ASTextNodeTruncation
 
 @interface ASTextNodeDrawParameters : NSObject
 
-- (instancetype)initWithRenderer:(ASTextKitRenderer *)renderer
-                      textOrigin:(CGPoint)textOrigin
-                 backgroundColor:(UIColor *)backgroundColor;
-
-@property (nonatomic, strong, readonly) ASTextKitRenderer *renderer;
-
-@property (nonatomic, assign, readonly) CGPoint textOrigin;
+@property (nonatomic, assign, readonly) CGRect bounds;
 
 @property (nonatomic, strong, readonly) UIColor *backgroundColor;
 
@@ -48,30 +42,16 @@ static NSString *ASTextNodeTruncationTokenAttributeName = @"ASTextNodeTruncation
 
 @implementation ASTextNodeDrawParameters
 
-- (instancetype)initWithRenderer:(ASTextKitRenderer *)renderer
-                      textOrigin:(CGPoint)textOrigin
-                 backgroundColor:(UIColor *)backgroundColor
+- (instancetype)initWithBounds:(CGRect)bounds
+               backgroundColor:(UIColor *)backgroundColor
 {
   if (self = [super init]) {
-    _renderer = renderer;
-    _textOrigin = textOrigin;
+    _bounds = bounds;
     _backgroundColor = backgroundColor;
   }
   return self;
 }
 
-- (void)dealloc
-{
-  // Destruction of the layout managers/containers/text storage is quite
-  // expensive, and can take some time, so we dispatch onto a bg queue to
-  // actually dealloc.
-  __block ASTextKitRenderer *renderer = _renderer;
-  ASPerformBlockOnBackgroundThread(^{
-    renderer = nil;
-  });
-  _renderer = nil;
-}
-
 @end
 
 @interface ASTextNode () <UIGestureRecognizerDelegate>
@@ -237,11 +217,17 @@ static NSArray *DefaultLinkAttributeNames = @[ NSLinkAttributeName ];
 
 #pragma mark - Renderer Management
 
+//only safe to call on the main thread
 - (ASTextKitRenderer *)_renderer
+{
+  return [self _rendererWithBounds:self.bounds];
+}
+
+- (ASTextKitRenderer *)_rendererWithBounds:(CGRect)bounds
 {
   ASDN::MutexLocker l(_rendererLock);
   if (_renderer == nil) {
-    CGSize constrainedSize = _constrainedSize.width != -INFINITY ? _constrainedSize : self.bounds.size;
+    CGSize constrainedSize = _constrainedSize.width != -INFINITY ? _constrainedSize : bounds.size;
     _renderer = [[ASTextKitRenderer alloc] initWithTextKitAttributes:[self _rendererAttributes]
                                                      constrainedSize:constrainedSize];
   }
@@ -420,13 +406,17 @@ static NSArray *DefaultLinkAttributeNames = @[ NSLinkAttributeName ];
 
 #pragma mark - Drawing
 
-+ (void)drawRect:(CGRect)bounds withParameters:(ASTextNodeDrawParameters *)parameters isCancelled:(asdisplaynode_iscancelled_block_t)isCancelledBlock isRasterizing:(BOOL)isRasterizing
+- (void)drawRect:(CGRect)bounds withParameters:(ASTextNodeDrawParameters *)parameters isCancelled:(asdisplaynode_iscancelled_block_t)isCancelledBlock isRasterizing:(BOOL)isRasterizing
 {
   CGContextRef context = UIGraphicsGetCurrentContext();
   ASDisplayNodeAssert(context, @"This is no good without a context.");
-
+  
   CGContextSaveGState(context);
-
+  
+  ASTextKitRenderer *renderer = [self _rendererWithBounds:parameters.bounds];
+  UIEdgeInsets shadowPadding = [self shadowPaddingWithRenderer:renderer];
+  CGPoint textOrigin = CGPointMake(parameters.bounds.origin.x - shadowPadding.left, parameters.bounds.origin.y - shadowPadding.top);
+  
   // Fill background
   if (!isRasterizing) {
     UIColor *backgroundColor = parameters.backgroundColor;
@@ -435,28 +425,20 @@ static NSArray *DefaultLinkAttributeNames = @[ NSLinkAttributeName ];
       UIRectFillUsingBlendMode(CGContextGetClipBoundingBox(context), kCGBlendModeCopy);
     }
   }
-
+  
   // Draw shadow
-  [[parameters.renderer shadower] setShadowInContext:context];
-
+  [[renderer shadower] setShadowInContext:context];
+  
   // Draw text
-  bounds.origin = parameters.textOrigin;
-  [parameters.renderer drawInContext:context bounds:bounds];
-
+  bounds.origin = textOrigin;
+  [renderer drawInContext:context bounds:bounds];
+  
   CGContextRestoreGState(context);
 }
 
 - (NSObject *)drawParametersForAsyncLayer:(_ASDisplayLayer *)layer
 {
-  CGRect bounds = self.bounds;
-  [self _invalidateRendererIfNeededForBoundsSize:bounds.size];
-
-  // Offset the text origin by any shadow padding
-  UIEdgeInsets shadowPadding = [self shadowPadding];
-  CGPoint textOrigin = CGPointMake(bounds.origin.x - shadowPadding.left, bounds.origin.y - shadowPadding.top);
-  return [[ASTextNodeDrawParameters alloc] initWithRenderer:[self _renderer]
-                                                 textOrigin:textOrigin
-                                            backgroundColor:self.backgroundColor];
+  return [[ASTextNodeDrawParameters alloc] initWithBounds:self.bounds backgroundColor:self.backgroundColor];
 }
 
 #pragma mark - Attributes
@@ -1016,9 +998,15 @@ static NSArray *DefaultLinkAttributeNames = @[ NSLinkAttributeName ];
   }
 }
 
+//only safe to call on main thread
 - (UIEdgeInsets)shadowPadding
 {
-  return [self _renderer].shadower.shadowPadding;
+  return [self shadowPaddingWithRenderer:[self _renderer]];
+}
+
+- (UIEdgeInsets)shadowPaddingWithRenderer:(ASTextKitRenderer *)renderer
+{
+  return renderer.shadower.shadowPadding;
 }
 
 #pragma mark - Truncation Message