Report precent difference when using a tolerance

FBSnapshotTestCase/Categories/UIImage+Compare.h

@@ -32,6 +32,13 @@
 
 @interface UIImage (Compare)
 
+/// Takes a tolerance percentage (0.0-1.0) and compares this image with another image. Returns YES if the images differ less than the tollerance.
 - (BOOL)fb_compareWithImage:(UIImage *)image tolerance:(CGFloat)tolerance;
 
+/// Performs a bitmap comparison of this image to another image. Returns YES if the images are exactly the same.
+- (BOOL)fb_isEqualToImage:(UIImage *)image;
+
+/// Returns the percent of total pixels that differ between this image and another image as a float ranging from 0.0 to 1.0.
+- (CGFloat)fb_differenceFromImage:(UIImage *)image;
+
 @end

FBSnapshotTestCase/Categories/UIImage+Compare.m

@@ -46,89 +46,64 @@ @implementation UIImage (Compare)
 
 - (BOOL)fb_compareWithImage:(UIImage *)image tolerance:(CGFloat)tolerance
 {
+ return [self fb_isEqualToImage:image] || (tolerance > 0.0 && [self fb_differenceFromImage:image] < tolerance);
+}
+
+
+- (BOOL)fb_isEqualToImage:(UIImage *)image {
  NSAssert(CGSizeEqualToSize(self.size, image.size), @"Images must be same size.");
 
- CGSize referenceImageSize = CGSizeMake(CGImageGetWidth(self.CGImage), CGImageGetHeight(self.CGImage));
- CGSize imageSize = CGSizeMake(CGImageGetWidth(image.CGImage), CGImageGetHeight(image.CGImage));
-
- // The images have the equal size, so we could use the smallest amount of bytes because of byte padding
- size_t minBytesPerRow = MIN(CGImageGetBytesPerRow(self.CGImage), CGImageGetBytesPerRow(image.CGImage));
- size_t referenceImageSizeBytes = referenceImageSize.height * minBytesPerRow;
- void *referenceImagePixels = calloc(1, referenceImageSizeBytes);
- void *imagePixels = calloc(1, referenceImageSizeBytes);
-
- if (!referenceImagePixels || !imagePixels) {
- free(referenceImagePixels);
- free(imagePixels);
- return NO;
- }
+ CGContextRef referenceContext = [self fb_bitmapContext];
+ CGContextRef imageContext = [image fb_bitmapContext];
 
- CGContextRef referenceImageContext = CGBitmapContextCreate(referenceImagePixels,
- referenceImageSize.width,
- referenceImageSize.height,
- CGImageGetBitsPerComponent(self.CGImage),
- minBytesPerRow,
- CGImageGetColorSpace(self.CGImage),
- (CGBitmapInfo)kCGImageAlphaPremultipliedLast
- );
- CGContextRef imageContext = CGBitmapContextCreate(imagePixels,
- imageSize.width,
- imageSize.height,
- CGImageGetBitsPerComponent(image.CGImage),
- minBytesPerRow,
- CGImageGetColorSpace(image.CGImage),
- (CGBitmapInfo)kCGImageAlphaPremultipliedLast
- );
-
- if (!referenceImageContext || !imageContext) {
- CGContextRelease(referenceImageContext);
- CGContextRelease(imageContext);
- free(referenceImagePixels);
- free(imagePixels);
- return NO;
- }
-
- CGContextDrawImage(referenceImageContext, CGRectMake(0, 0, referenceImageSize.width, referenceImageSize.height), self.CGImage);
- CGContextDrawImage(imageContext, CGRectMake(0, 0, imageSize.width, imageSize.height), image.CGImage);
-
- CGContextRelease(referenceImageContext);
+ size_t pixelCount = CGBitmapContextGetHeight(referenceContext) * CGBitmapContextGetBytesPerRow(referenceContext);
+ BOOL matches = (memcmp(CGBitmapContextGetData(referenceContext), CGBitmapContextGetData(imageContext), pixelCount) == 0);
+
+ CGContextRelease(referenceContext);
  CGContextRelease(imageContext);
+
+ return matches;
+}
 
- BOOL imageEqual = YES;
-
- // Do a fast compare if we can
- if (tolerance == 0) {
- imageEqual = (memcmp(referenceImagePixels, imagePixels, referenceImageSizeBytes) == 0);
- } else {
- // Go through each pixel in turn and see if it is different
- const NSInteger pixelCount = referenceImageSize.width * referenceImageSize.height;
-
- FBComparePixel *p1 = referenceImagePixels;
- FBComparePixel *p2 = imagePixels;
-
- NSInteger numDiffPixels = 0;
- for (int n = 0; n < pixelCount; ++n) {
- // If this pixel is different, increment the pixel diff count and see
- // if we have hit our limit.
- if (p1->raw != p2->raw) {
- numDiffPixels ++;
-
- CGFloat percent = (CGFloat)numDiffPixels / pixelCount;
- if (percent > tolerance) {
- imageEqual = NO;
- break;
- }
- }
+- (CGFloat)fb_differenceFromImage:(UIImage *)image {
+ NSAssert(CGSizeEqualToSize(self.size, image.size), @"Images must be same size.");
 
- p1++;
- p2++;
+ // Go through each pixel in turn and see if it is different
+ CGContextRef referenceContext = [self fb_bitmapContext];
+ CGContextRef imageContext = [image fb_bitmapContext];
+
+ FBComparePixel *p1 = CGBitmapContextGetData(referenceContext);
+ FBComparePixel *p2 = CGBitmapContextGetData(imageContext);
+
+ NSInteger pixelCount = CGBitmapContextGetWidth(referenceContext) * CGBitmapContextGetHeight(referenceContext);
+ NSInteger numDiffPixels = 0;
+ for (int n = 0; n < pixelCount; ++n) {
+ // If this pixel is different, increment the pixel diff count and see
+ // if we have hit our limit.
+ if (p1->raw != p2->raw) {
+ numDiffPixels++;
  }
+
+ p1++;
+ p2++;
  }
+
+ return (CGFloat)numDiffPixels / pixelCount;
+}
 
- free(referenceImagePixels);
- free(imagePixels);
-
- return imageEqual;
+- (CGContextRef)fb_bitmapContext {
+ CGContextRef context = CGBitmapContextCreate(NULL,
+ self.size.width,
+ self.size.height,
+ CGImageGetBitsPerComponent(self.CGImage),
+ CGImageGetBytesPerRow(self.CGImage),
+ CGImageGetColorSpace(self.CGImage),
+ (CGBitmapInfo)kCGImageAlphaPremultipliedLast);
+
+ CGContextDrawImage(context, (CGRect){.size = self.size}, self.CGImage);
+
+ NSAssert(context != nil, @"Unable to create context for comparision.");
+ return context;
 }
 
 @end

FBSnapshotTestCase/FBSnapshotTestController.h

@@ -43,6 +43,11 @@ extern NSString *const FBCapturedImageKey;
  */
 extern NSString *const FBDiffedImageKey;
 
+/**
+ Errors returned by the methods of FBSnapshotTestController will contain this key if a tolerance was specified.
+ */
+extern NSString *const FBPercentDifferenceKey;
+
 /**
  Provides the heavy-lifting for FBSnapshotTestCase. It loads and saves images, along with performing the actual pixel-
  by-pixel comparison of images.

FBSnapshotTestCase/FBSnapshotTestController.m

@@ -21,6 +21,7 @@
 NSString *const FBReferenceImageKey = @"FBReferenceImageKey";
 NSString *const FBCapturedImageKey = @"FBCapturedImageKey";
 NSString *const FBDiffedImageKey = @"FBDiffedImageKey";
+NSString *const FBPercentDifferenceKey = @"FBPercentDifferenceKey";
 
 typedef NS_ENUM(NSUInteger, FBTestSnapshotFileNameType) {
  FBTestSnapshotFileNameTypeReference,
@@ -130,25 +131,44 @@ - (BOOL)compareReferenceImage:(UIImage *)referenceImage
  error:(NSError **)errorPtr
 {
  BOOL sameImageDimensions = CGSizeEqualToSize(referenceImage.size, image.size);
- if (sameImageDimensions && [referenceImage fb_compareWithImage:image tolerance:tolerance]) {
+ if (sameImageDimensions && [referenceImage fb_isEqualToImage:image]) {
  return YES;
  }
 
+ CGFloat percentDifference;
+ if (tolerance > 0.0) {
+ percentDifference = [referenceImage fb_differenceFromImage:image];
+ if (percentDifference < tolerance) {
+ return YES;
+ }
+ }
+
  if (NULL != errorPtr) {
  NSString *errorDescription = sameImageDimensions ? @"Images different" : @"Images different sizes";
- NSString *errorReason = sameImageDimensions ? [NSString stringWithFormat:@"image pixels differed by more than %.2f%% from the reference image", tolerance * 100]
+ NSString *errorReason = sameImageDimensions ? @"Images differed"
  : [NSString stringWithFormat:@"referenceImage:%@, image:%@", NSStringFromCGSize(referenceImage.size), NSStringFromCGSize(image.size)];
  FBSnapshotTestControllerErrorCode errorCode = sameImageDimensions ? FBSnapshotTestControllerErrorCodeImagesDifferent : FBSnapshotTestControllerErrorCodeImagesDifferentSizes;
 
- *errorPtr = [NSError errorWithDomain:FBSnapshotTestControllerErrorDomain
- code:errorCode
- userInfo:@{
- NSLocalizedDescriptionKey: errorDescription,
- NSLocalizedFailureReasonErrorKey: errorReason,
- FBReferenceImageKey: referenceImage,
- FBCapturedImageKey: image,
- FBDiffedImageKey: [referenceImage fb_diffWithImage:image],
- }];
+ if (sameImageDimensions && tolerance > 0.0) {
+ *errorPtr = [NSError errorWithDomain:FBSnapshotTestControllerErrorDomain
+ code:errorCode
+ userInfo:@{
+ NSLocalizedDescriptionKey: errorDescription,
+ NSLocalizedFailureReasonErrorKey: [NSString stringWithFormat:@"Images differed by %.2f%% from the reference (with a tolerance of %.2f%%)", percentDifference * 100, tolerance * 100],
+ FBReferenceImageKey: referenceImage,
+ FBCapturedImageKey: image,
+ FBPercentDifferenceKey: @(percentDifference * 100),
+ }];
+ } else {
+ *errorPtr = [NSError errorWithDomain:FBSnapshotTestControllerErrorDomain
+ code:errorCode
+ userInfo:@{
+ NSLocalizedDescriptionKey: errorDescription,
+ NSLocalizedFailureReasonErrorKey: errorReason,
+ FBReferenceImageKey: referenceImage,
+ FBCapturedImageKey: image,
+ }];
+ }
  }
  return NO;
 }

FBSnapshotTestCaseTests/FBSnapshotControllerTests.m

@@ -60,6 +60,7 @@ - (void)testCompareReferenceImageWithVeryLowToleranceShouldNotMatch
  XCTAssertFalse([controller compareReferenceImage:referenceImage toImage:testImage tolerance:0.0001 error:&error]);
  XCTAssertNotNil(error);
  XCTAssertEqual(error.code, FBSnapshotTestControllerErrorCodeImagesDifferent);
+ XCTAssertEqual([error.userInfo[FBPercentDifferenceKey] doubleValue], .04);
 }
 
 - (void)testCompareReferenceImageWithVeryLowToleranceShouldMatch