[ASImageNode] A ASImageNode debug feature showing pixel scaling amount

- shows a red text label overlay on bottom right hand corner of ASImageNodes with pixel scaling factor
- import AsyncDisplayKit+Debug.h and enable using [ASImageNode setEnableImageDebugOverlay]

AsyncDisplayKit/ASImageNode.mm

@@ -15,8 +15,10 @@
 #import <AsyncDisplayKit/ASDisplayNodeInternal.h>
 #import <AsyncDisplayKit/ASDisplayNodeExtras.h>
 #import <AsyncDisplayKit/ASDisplayNode+Beta.h>
+#import <AsyncDisplayKit/ASTextNode.h>
 
 #import "ASImageNode+CGExtras.h"
+#import "AsyncDisplayKit+Debug.h"
 
 #import "ASInternalHelpers.h"
 #import "ASEqualityHelpers.h"
@@ -55,6 +57,9 @@
 
 @end
 
+@interface ASImageNode ()
+@property (nonatomic, strong) ASTextNode *debugLabelNode;
+@end
 
 @implementation ASImageNode
 {
@@ -90,6 +95,12 @@
   _cropDisplayBounds = CGRectNull;
   _placeholderColor = ASDisplayNodeDefaultPlaceholderColor();
   
+  if ([ASImageNode shouldShowImageDebugOverlay]) {
+    _debugLabelNode = [[ASTextNode alloc] init];
+    _debugLabelNode.layerBacked = YES;
+    [self addSubnode:_debugLabelNode];
+  }
+
   return self;
 }
 
@@ -109,6 +120,7 @@
 {
   ASDN::MutexLocker l(_imageLock);
   // if a preferredFrameSize is set, call the superclass to return that instead of using the image size.
+  [_debugLabelNode measure:constrainedSize];
   if (CGSizeEqualToSize(self.preferredFrameSize, CGSizeZero) == NO)
     return [super calculateSizeThatFits:constrainedSize];
   else if (_image)
@@ -152,6 +164,12 @@
                                                 contentMode:self.contentMode];
 }
 
+- (NSDictionary *)debugLabelAttributes
+{
+  return @{ NSFontAttributeName: [UIFont systemFontOfSize:15.0],
+            NSForegroundColorAttributeName: [UIColor redColor] };
+}
+
 - (UIImage *)displayWithParameters:(_ASImageNodeDrawParameters *)parameters isCancelled:(asdisplaynode_iscancelled_block_t)isCancelled
 {
   UIImage *image;
@@ -202,6 +220,20 @@
   CGSize imageSizeInPixels = CGSizeMake(imageSize.width * image.scale, imageSize.height * image.scale);
   CGSize boundsSizeInPixels = CGSizeMake(floorf(bounds.size.width * contentsScale), floorf(bounds.size.height * contentsScale));
   
+  if (_debugLabelNode) {
+  //  NSLog(@"widthScale = %f, heightScale = %f", imageSizeInPixels.width / boundsSizeInPixels.width, imageSizeInPixels.height / boundsSizeInPixels.height);
+    CGFloat pixelCountRatio            = (imageSizeInPixels.width * imageSizeInPixels.height) / (boundsSizeInPixels.width * boundsSizeInPixels.height);
+    if (pixelCountRatio != 1.0) {
+      NSString *scaleString            = [NSString stringWithFormat:@"%.2fx", pixelCountRatio];
+      _debugLabelNode.attributedString = [[NSAttributedString alloc] initWithString:scaleString attributes:[self debugLabelAttributes]];
+      _debugLabelNode.hidden           = NO;
+      [self setNeedsLayout];
+    } else {
+      _debugLabelNode.hidden           = YES;
+      _debugLabelNode.attributedString = nil;
+    }
+  }
+  
   BOOL contentModeSupported =    contentMode == UIViewContentModeScaleAspectFill
   || contentMode == UIViewContentModeScaleAspectFit
   || contentMode == UIViewContentModeCenter;
@@ -410,8 +442,20 @@
   _imageModificationBlock = imageModificationBlock;
 }
 
-@end
+#pragma mark - Debug
+- (void)layout
+{
+  [super layout];
   
+  if (_debugLabelNode) {
+    CGSize boundsSize        = self.bounds.size;
+    CGSize debugLabelSize    = [_debugLabelNode measure:boundsSize];
+    CGPoint debugLabelOrigin = CGPointMake(boundsSize.width - debugLabelSize.width,
+                                           boundsSize.height - debugLabelSize.height);
+    _debugLabelNode.frame    = (CGRect) {debugLabelOrigin, debugLabelSize};
+  }
+}
+@end
 
 #pragma mark - Extras
 extern asimagenode_modification_block_t ASImageNodeRoundBorderModificationBlock(CGFloat borderWidth, UIColor *borderColor)
@@ -460,4 +504,3 @@ extern asimagenode_modification_block_t ASImageNodeTintColorModificationBlock(UI
     return modifiedImage;
   };
 }
-

AsyncDisplayKit/AsyncDisplayKit+Debug.h

@@ -0,0 +1,21 @@
+//
+//  AsyncDisplayKit+Debug.h
+//  AsyncDisplayKit
+//
+//  Created by Hannah Troisi on 3/7/16.
+//  Copyright © 2016 Facebook. All rights reserved.
+//
+
+#import <Foundation/Foundation.h>
+#import "ASImageNode.h"
+
+@interface ASImageNode (Debug)
+
+/**
+* Class method to enable visualization of an ASImageNode's image size. For app debugging purposes only.
+* @param enabled Specify YES to turn on this debug feature when messaging the ASImageNode class.
+*/
++ (void)setImageDebugEnabled:(BOOL)enable;
++ (BOOL)shouldShowImageDebugOverlay;
+
+@end

AsyncDisplayKit/AsyncDisplayKit+Debug.m

@@ -0,0 +1,27 @@
+//
+//  AsyncDisplayKit+Debug.m
+//  AsyncDisplayKit
+//
+//  Created by Hannah Troisi on 3/7/16.
+//  Copyright © 2016 Facebook. All rights reserved.
+//
+
+#import "AsyncDisplayKit+Debug.h"
+#import "ASDisplayNode+Subclasses.h"
+#import "ASTextNode.h"
+
+static BOOL __enableImageSizeOverlay = NO;
+
+@implementation ASImageNode (Debug)
+
++ (void)setImageDebugEnabled:(BOOL)enable;
+{
+  __enableImageSizeOverlay = enable;
+}
+
++ (BOOL)shouldShowImageDebugOverlay
+{
+  return __enableImageSizeOverlay;
+}
+
+@end