Debugging mode for CALayers: highlights borders and dumps sublayers as images

CALayer-YXDebug.h

#import <UIKit/UIKit.h>
#import <QuartzCore/QuartzCore.h>

@interface CALayer (YXDebug)

- (UIImage *)snapshot;
- (void)dumpSublayerImagesToFolder:(NSString *)folderPath;
- (void)highlightSublayerBorders;

@end

CALayer-YXDebug.m

#import "CALayer-YXDebug.h"

@implementation CALayer (YXDebug)

- (UIImage *)snapshot {
	CGSize size = self.bounds.size;
	
	if (CGSizeEqualToSize(size, CGSizeZero)) {
		return nil;
	}
	
	if (UIGraphicsBeginImageContextWithOptions != NULL) {
		UIGraphicsBeginImageContextWithOptions(size, NO, 0.0f);
	} else {
		UIGraphicsBeginImageContext(size);
	}
	
	[self renderInContext:UIGraphicsGetCurrentContext()];
	
	UIImage * image = UIGraphicsGetImageFromCurrentImageContext();
	NSAssert(image != nil, @"Image mustn't be nil");
	
	UIGraphicsEndImageContext();
	
	return [[image retain] autorelease];
}

- (void)collectSublayerImagesTo:(NSMutableDictionary *)dict prefix:(NSString *)prefix {
	NSUInteger count = [dict count];
	NSString * className = [[self class] description];
	NSString * key = nil;

	if (prefix) {
		key = [NSString stringWithFormat:@"%d-%@-%@", count, prefix, className];
	} else {
		key = [NSString stringWithFormat:@"%d-%@", count, className];
	}

	UIImage * image = [self snapshot];
	if (image == nil) {
		return;
	}

	[dict setObject:image forKey:key];
	
	NSString * newPrefix = nil;
	if (prefix) {
		newPrefix = [prefix stringByAppendingFormat:@"-%@", className];
	} else {
		newPrefix = className;
	}
	
	for (CALayer * layer in [self sublayers]) {
		[layer collectSublayerImagesTo:dict prefix:newPrefix];
	}
}

- (NSDictionary *)sublayerImages {
	NSMutableDictionary * dict = [NSMutableDictionary dictionaryWithCapacity:10];
	[self collectSublayerImagesTo:dict prefix:nil];
	return [NSDictionary dictionaryWithDictionary:dict];
}

- (void)dumpSublayerImagesToFolder:(NSString*)folderPath {
	NSDictionary * sublayerImages = [self sublayerImages];
	
	for (NSString * key in [sublayerImages allKeys]) {
		UIImage * image = [sublayerImages objectForKey:key];
		NSData * data = UIImagePNGRepresentation(image);
		NSString * path = [NSString stringWithFormat:@"%@/%@.png", folderPath, key];

		[data writeToFile:path atomically:YES];
	}
}
- (void)highlightSublayerBorders {
	self.borderColor = [[UIColor redColor] CGColor];
	self.borderWidth = 1.0;
	for (CALayer * layer in [self sublayers]) {
		[layer highlightSublayerBorders];
	}
}

@end