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Added Tolerance on individual pixel level (#43)
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@JerryTheIntern @alanzeino
JerryTheIntern authored and alanzeino committed Jan 10, 2019
1 parent 8c5aaff commit 8c5bdf3
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Showing 10 changed files with 343 additions and 54 deletions.
6 changes: 6 additions & 0 deletions FBSnapshotTestCase.xcodeproj/project.pbxproj
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Expand Up @@ -15,6 +15,8 @@
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827137921C63ABF000354E42 /* UIImage+Diff.h in Headers */ = {isa = PBXBuildFile; fileRef = 133564121B59C3F500A4E4BF /* UIImage+Diff.h */; };
Expand Down Expand Up @@ -75,6 +77,7 @@
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B32447D91AB78B5E00B1D6FF /* square_with_text.png */,
Expand Down Expand Up @@ -379,6 +383,7 @@
827137A21C63AC0D00354E42 /* square-copy.png in Resources */,
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Expand All @@ -398,6 +403,7 @@
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2 changes: 1 addition & 1 deletion FBSnapshotTestCase/Categories/UIImage+Compare.h
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Expand Up @@ -34,7 +34,7 @@ NS_ASSUME_NONNULL_BEGIN

@interface UIImage (Compare)

- (BOOL)fb_compareWithImage:(UIImage *)image tolerance:(CGFloat)tolerance;
- (BOOL)fb_compareWithImage:(UIImage *)image pixelTolerance:(CGFloat)pixelTolerance tolerance:(CGFloat)tolerance;

@end

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96 changes: 72 additions & 24 deletions FBSnapshotTestCase/Categories/UIImage+Compare.m
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Expand Up @@ -44,7 +44,7 @@

@implementation UIImage (Compare)

- (BOOL)fb_compareWithImage:(UIImage *)image tolerance:(CGFloat)tolerance
- (BOOL)fb_compareWithImage:(UIImage *)image pixelTolerance:(CGFloat)pixelTolerance tolerance:(CGFloat)tolerance
{
NSAssert(CGSizeEqualToSize(self.size, image.size), @"Images must be same size.");

Expand Down Expand Up @@ -93,34 +93,20 @@ - (BOOL)fb_compareWithImage:(UIImage *)image tolerance:(CGFloat)tolerance
CGContextRelease(imageContext);

BOOL imageEqual = YES;
FBComparePixel *p1 = referenceImagePixels;
FBComparePixel *p2 = imagePixels;

// Do a fast compare if we can
if (tolerance == 0) {
if (tolerance == 0 && pixelTolerance == 0) {
imageEqual = (memcmp(referenceImagePixels, imagePixels, referenceImageSizeBytes) == 0);
} else {
const NSUInteger pixelCount = referenceImageSize.width * referenceImageSize.height;
// 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;
}
}

p1++;
p2++;
}
imageEqual = [self _compareAllPixelsWithPixelTolerance:pixelTolerance
tolerance:tolerance
pixelCount:pixelCount
referencePixels:p1
imagePixels:p2];
}

free(referenceImagePixels);
Expand All @@ -129,4 +115,66 @@ - (BOOL)fb_compareWithImage:(UIImage *)image tolerance:(CGFloat)tolerance
return imageEqual;
}

- (BOOL)_comparePixelWithPixelTolerance:(CGFloat)pixelTolerance
referencePixel:(FBComparePixel *)referencePixel
imagePixel:(FBComparePixel *)imagePixel
{
if (referencePixel->raw == imagePixel->raw) {
return YES;
} else if (pixelTolerance == 0) {
return NO;
}

CGFloat redPercentDiff = [self _calculatePercentDifferenceForReferencePixelComponent:referencePixel->pixels.red
imagePixelComponent:imagePixel->pixels.red];
CGFloat greenPercentDiff = [self _calculatePercentDifferenceForReferencePixelComponent:referencePixel->pixels.green
imagePixelComponent:imagePixel->pixels.green];
CGFloat bluePercentDiff = [self _calculatePercentDifferenceForReferencePixelComponent:referencePixel->pixels.blue
imagePixelComponent:imagePixel->pixels.blue];
CGFloat alphaPercentDiff = [self _calculatePercentDifferenceForReferencePixelComponent:referencePixel->pixels.alpha
imagePixelComponent:imagePixel->pixels.alpha];

BOOL anyDifferencesFound = (redPercentDiff > pixelTolerance ||
greenPercentDiff > pixelTolerance ||
bluePercentDiff > pixelTolerance ||
alphaPercentDiff > pixelTolerance);

return !anyDifferencesFound;
}

- (CGFloat)_calculatePercentDifferenceForReferencePixelComponent:(char)p1
imagePixelComponent:(char)p2
{
NSInteger referencePixelComponent = (unsigned char)p1;
NSInteger imagePixelComponent = (unsigned char)p2;
NSUInteger componentDifference = ABS(referencePixelComponent - imagePixelComponent);
return (CGFloat)componentDifference / 256;
}

- (BOOL)_compareAllPixelsWithPixelTolerance:(CGFloat)pixelTolerance
tolerance:(CGFloat)tolerance
pixelCount:(NSUInteger)pixelCount
referencePixels:(FBComparePixel *)referencePixel
imagePixels:(FBComparePixel *)imagePixel
{
NSUInteger numDiffPixels = 0;
for (NSUInteger n = 0; n < pixelCount; ++n) {
// If this pixel is different, increment the pixel diff count and see
// if we have hit our limit.
BOOL isIdenticalPixel = [self _comparePixelWithPixelTolerance:pixelTolerance referencePixel:referencePixel imagePixel:imagePixel];
if (!isIdenticalPixel) {
numDiffPixels++;

CGFloat percent = (CGFloat)numDiffPixels / (CGFloat)pixelCount;
if (percent > tolerance) {
return NO;
}
}

referencePixel++;
imagePixel++;
}
return YES;
}

@end

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