YYText/Demo/YYTextDemo/UIImage+YYWebImage.m

//
//  UIImage+YYWebImage.m
//  YYWebImage <https://github.com/ibireme/YYWebImage>
//
//  Created by ibireme on 13/4/4.
//  Copyright (c) 2015 ibireme.
//
//  This source code is licensed under the MIT-style license found in the
//  LICENSE file in the root directory of this source tree.
//

#import "UIImage+YYWebImage.h"
#import <ImageIO/ImageIO.h>
#import <Accelerate/Accelerate.h>
#import <objc/runtime.h>



/// Convert degrees to radians.
static inline CGFloat _DegreesToRadians(CGFloat degrees) {
    return degrees * M_PI / 180;
}


/**
 Resize rect to fit the size using a given contentMode.
 
 @param rect The draw rect
 @param size The content size
 @param mode The content mode
 @return A resized rect for the given content mode.
 @discussion UIViewContentModeRedraw is same as UIViewContentModeScaleToFill.
 */
static CGRect _YYCGRectFitWithContentMode(CGRect rect, CGSize size, UIViewContentMode mode) {
    rect = CGRectStandardize(rect);
    size.width = size.width < 0 ? -size.width : size.width;
    size.height = size.height < 0 ? -size.height : size.height;
    CGPoint center = CGPointMake(CGRectGetMidX(rect), CGRectGetMidY(rect));
    switch (mode) {
        case UIViewContentModeScaleAspectFit:
        case UIViewContentModeScaleAspectFill: {
            if (rect.size.width < 0.01 || rect.size.height < 0.01 ||
                size.width < 0.01 || size.height < 0.01) {
                rect.origin = center;
                rect.size = CGSizeZero;
            } else {
                CGFloat scale;
                if (size.width / size.height < rect.size.width / rect.size.height &&
                    mode == UIViewContentModeScaleAspectFit) {
                    scale = rect.size.height / size.height;
                } else {
                    scale = rect.size.width / size.width;
                }
                size.width *= scale;
                size.height *= scale;
                rect.size = size;
                rect.origin = CGPointMake(center.x - size.width * 0.5, center.y - size.height * 0.5);
            }
        } break;
        case UIViewContentModeCenter: {
            rect.size = size;
            rect.origin = CGPointMake(center.x - size.width * 0.5, center.y - size.height * 0.5);
        } break;
        case UIViewContentModeTop: {
            rect.origin.x = center.x - size.width * 0.5;
            rect.size = size;
        } break;
        case UIViewContentModeBottom: {
            rect.origin.x = center.x - size.width * 0.5;
            rect.origin.y += rect.size.height - size.height;
            rect.size = size;
        } break;
        case UIViewContentModeLeft: {
            rect.origin.y = center.y - size.height * 0.5;
            rect.size = size;
        } break;
        case UIViewContentModeRight: {
            rect.origin.y = center.y - size.height * 0.5;
            rect.origin.x += rect.size.width - size.width;
            rect.size = size;
        } break;
        case UIViewContentModeTopLeft: {
            rect.size = size;
        } break;
        case UIViewContentModeTopRight: {
            rect.origin.x += rect.size.width - size.width;
            rect.size = size;
        } break;
        case UIViewContentModeBottomLeft: {
            rect.origin.y += rect.size.height - size.height;
            rect.size = size;
        } break;
        case UIViewContentModeBottomRight: {
            rect.origin.x += rect.size.width - size.width;
            rect.origin.y += rect.size.height - size.height;
            rect.size = size;
        } break;
        case UIViewContentModeScaleToFill:
        case UIViewContentModeRedraw:
        default: {
            rect = rect;
        }
    }
    return rect;
}




static NSTimeInterval _yy_CGImageSourceGetGIFFrameDelayAtIndex(CGImageSourceRef source, size_t index) {
    NSTimeInterval delay = 0;
    CFDictionaryRef dic = CGImageSourceCopyPropertiesAtIndex(source, index, NULL);
    if (dic) {
        CFDictionaryRef dicGIF = CFDictionaryGetValue(dic, kCGImagePropertyGIFDictionary);
        if (dicGIF) {
            NSNumber *num = CFDictionaryGetValue(dicGIF, kCGImagePropertyGIFUnclampedDelayTime);
            if (num.doubleValue <= __FLT_EPSILON__) {
                num = CFDictionaryGetValue(dicGIF, kCGImagePropertyGIFDelayTime);
            }
            delay = num.doubleValue;
        }
        CFRelease(dic);
    }
    
    // http://nullsleep.tumblr.com/post/16524517190/animated-gif-minimum-frame-delay-browser-compatibility
    if (delay < 0.02) delay = 0.1;
    return delay;
}



@implementation UIImage (YYWebImage)

+ (UIImage *)yy_imageWithSmallGIFData:(NSData *)data scale:(CGFloat)scale {
    CGImageSourceRef source = CGImageSourceCreateWithData((__bridge CFTypeRef)(data), NULL);
    if (!source) return nil;
    
    size_t count = CGImageSourceGetCount(source);
    if (count <= 1) {
        CFRelease(source);
        return [self.class imageWithData:data scale:scale];
    }
    
    NSUInteger frames[count];
    double oneFrameTime = 1 / 50.0; // 50 fps
    NSTimeInterval totalTime = 0;
    NSUInteger totalFrame = 0;
    NSUInteger gcdFrame = 0;
    for (size_t i = 0; i < count; i++) {
        NSTimeInterval delay = _yy_CGImageSourceGetGIFFrameDelayAtIndex(source, i);
        totalTime += delay;
        NSInteger frame = lrint(delay / oneFrameTime);
        if (frame < 1) frame = 1;
        frames[i] = frame;
        totalFrame += frames[i];
        if (i == 0) gcdFrame = frames[i];
        else {
            NSUInteger frame = frames[i], tmp;
            if (frame < gcdFrame) {
                tmp = frame; frame = gcdFrame; gcdFrame = tmp;
            }
            while (true) {
                tmp = frame % gcdFrame;
                if (tmp == 0) break;
                frame = gcdFrame;
                gcdFrame = tmp;
            }
        }
    }
    NSMutableArray *array = [NSMutableArray new];
    for (size_t i = 0; i < count; i++) {
        CGImageRef imageRef = CGImageSourceCreateImageAtIndex(source, i, NULL);
        if (!imageRef) {
            CFRelease(source);
            return nil;
        }
        size_t width = CGImageGetWidth(imageRef);
        size_t height = CGImageGetHeight(imageRef);
        if (width == 0 || height == 0) {
            CFRelease(source);
            CFRelease(imageRef);
            return nil;
        }
        
        CGImageAlphaInfo alphaInfo = CGImageGetAlphaInfo(imageRef) & kCGBitmapAlphaInfoMask;
        BOOL hasAlpha = NO;
        if (alphaInfo == kCGImageAlphaPremultipliedLast ||
            alphaInfo == kCGImageAlphaPremultipliedFirst ||
            alphaInfo == kCGImageAlphaLast ||
            alphaInfo == kCGImageAlphaFirst) {
            hasAlpha = YES;
        }
        // BGRA8888 (premultiplied) or BGRX8888
        // same as UIGraphicsBeginImageContext() and -[UIView drawRect:]
        CGBitmapInfo bitmapInfo = kCGBitmapByteOrder32Host;
        bitmapInfo |= hasAlpha ? kCGImageAlphaPremultipliedFirst : kCGImageAlphaNoneSkipFirst;
        CGColorSpaceRef space = CGColorSpaceCreateDeviceRGB();
        CGContextRef context = CGBitmapContextCreate(NULL, width, height, 8, 0, space, bitmapInfo);
        CGColorSpaceRelease(space);
        if (!context) {
            CFRelease(source);
            CFRelease(imageRef);
            return nil;
        }
        CGContextDrawImage(context, CGRectMake(0, 0, width, height), imageRef); // decode
        CGImageRef decoded = CGBitmapContextCreateImage(context);
        CFRelease(context);
        if (!decoded) {
            CFRelease(source);
            CFRelease(imageRef);
            return nil;
        }
        UIImage *image = image = [UIImage imageWithCGImage:decoded scale:scale orientation:UIImageOrientationUp];
        CGImageRelease(imageRef);
        CGImageRelease(decoded);
        if (!image) {
            CFRelease(source);
            return nil;
        }
        for (size_t j = 0, max = frames[i] / gcdFrame; j < max; j++) {
            [array addObject:image];
        }
    }
    CFRelease(source);
    UIImage *image = [self.class animatedImageWithImages:array duration:totalTime];
    return image;
}

+ (UIImage *)yy_imageWithColor:(UIColor *)color {
    return [self yy_imageWithColor:color size:CGSizeMake(1, 1)];
}

+ (UIImage *)yy_imageWithColor:(UIColor *)color size:(CGSize)size {
    if (!color || size.width <= 0 || size.height <= 0) return nil;
    CGRect rect = CGRectMake(0.0f, 0.0f, size.width, size.height);
    UIGraphicsBeginImageContextWithOptions(rect.size, NO, 0);
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSetFillColorWithColor(context, color.CGColor);
    CGContextFillRect(context, rect);
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return image;
}

+ (UIImage *)yy_imageWithSize:(CGSize)size drawBlock:(void (^)(CGContextRef context))drawBlock {
    if (!drawBlock) return nil;
    UIGraphicsBeginImageContextWithOptions(size, NO, 0);
    CGContextRef context = UIGraphicsGetCurrentContext();
    if (!context) return nil;
    drawBlock(context);
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return image;
}

- (BOOL)yy_hasAlphaChannel {
    if (self.CGImage == NULL) return NO;
    CGImageAlphaInfo alpha = CGImageGetAlphaInfo(self.CGImage) & kCGBitmapAlphaInfoMask;
    return (alpha == kCGImageAlphaFirst ||
            alpha == kCGImageAlphaLast ||
            alpha == kCGImageAlphaPremultipliedFirst ||
            alpha == kCGImageAlphaPremultipliedLast);
}

- (void)yy_drawInRect:(CGRect)rect withContentMode:(UIViewContentMode)contentMode clipsToBounds:(BOOL)clips{
    CGRect drawRect = _YYCGRectFitWithContentMode(rect, self.size, contentMode);
    if (drawRect.size.width == 0 || drawRect.size.height == 0) return;
    if (clips) {
        CGContextRef context = UIGraphicsGetCurrentContext();
        if (context) {
            CGContextSaveGState(context);
            CGContextAddRect(context, rect);
            CGContextClip(context);
            [self drawInRect:drawRect];
            CGContextRestoreGState(context);
        }
    } else {
        [self drawInRect:drawRect];
    }
}

- (UIImage *)yy_imageByResizeToSize:(CGSize)size {
    if (size.width <= 0 || size.height <= 0) return nil;
    UIGraphicsBeginImageContextWithOptions(size, NO, self.scale);
    [self drawInRect:CGRectMake(0, 0, size.width, size.height)];
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return image;
}

- (UIImage *)yy_imageByResizeToSize:(CGSize)size contentMode:(UIViewContentMode)contentMode {
    if (size.width <= 0 || size.height <= 0) return nil;
    UIGraphicsBeginImageContextWithOptions(size, NO, self.scale);
    [self yy_drawInRect:CGRectMake(0, 0, size.width, size.height) withContentMode:contentMode clipsToBounds:NO];
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return image;
}

- (UIImage *)yy_imageByCropToRect:(CGRect)rect {
    rect.origin.x *= self.scale;
    rect.origin.y *= self.scale;
    rect.size.width *= self.scale;
    rect.size.height *= self.scale;
    if (rect.size.width <= 0 || rect.size.height <= 0) return nil;
    CGImageRef imageRef = CGImageCreateWithImageInRect(self.CGImage, rect);
    UIImage *image = [UIImage imageWithCGImage:imageRef scale:self.scale orientation:self.imageOrientation];
    CGImageRelease(imageRef);
    return image;
}

- (UIImage *)yy_imageByInsetEdge:(UIEdgeInsets)insets withColor:(UIColor *)color {
    CGSize size = self.size;
    size.width -= insets.left + insets.right;
    size.height -= insets.top + insets.bottom;
    if (size.width <= 0 || size.height <= 0) return nil;
    CGRect rect = CGRectMake(-insets.left, -insets.top, self.size.width, self.size.height);
    UIGraphicsBeginImageContextWithOptions(size, NO, self.scale);
    CGContextRef context = UIGraphicsGetCurrentContext();
    if (color) {
        CGContextSetFillColorWithColor(context, color.CGColor);
        CGMutablePathRef path = CGPathCreateMutable();
        CGPathAddRect(path, NULL, CGRectMake(0, 0, size.width, size.height));
        CGPathAddRect(path, NULL, rect);
        CGContextAddPath(context, path);
        CGContextEOFillPath(context);
        CGPathRelease(path);
    }
    [self drawInRect:rect];
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return image;
}

- (UIImage *)yy_imageByRoundCornerRadius:(CGFloat)radius {
    return [self yy_imageByRoundCornerRadius:radius corners:UIRectCornerAllCorners borderWidth:0];
}

- (UIImage *)yy_imageByRoundCornerRadius:(CGFloat)radius corners:(UIRectCorner)corners borderWidth:(CGFloat)borderWidth {
    UIGraphicsBeginImageContextWithOptions(self.size, NO, self.scale);
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGRect rect = CGRectMake(0, 0, self.size.width, self.size.height);
    CGContextScaleCTM(context, 1, -1);
    CGContextTranslateCTM(context, 0, -rect.size.height);
    
    CGFloat minSize = MIN(self.size.width, self.size.height);
    if (borderWidth < minSize / 2) {
        [[UIBezierPath bezierPathWithRoundedRect:CGRectInset(rect, borderWidth, borderWidth) byRoundingCorners:corners cornerRadii:CGSizeMake(radius, borderWidth)] addClip];
        CGContextDrawImage(context, rect, self.CGImage);
    }
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return image;
}

- (UIImage *)yy_imageByRotate:(CGFloat)radians fitSize:(BOOL)fitSize {
    size_t width = (size_t)CGImageGetWidth(self.CGImage);
    size_t height = (size_t)CGImageGetHeight(self.CGImage);
    CGRect newRect = CGRectApplyAffineTransform(CGRectMake(0., 0., width, height),
                                                fitSize ? CGAffineTransformMakeRotation(radians) : CGAffineTransformIdentity);
    
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(NULL,
                                                 (size_t)newRect.size.width,
                                                 (size_t)newRect.size.height,
                                                 8,
                                                 (size_t)newRect.size.width * 4,
                                                 colorSpace,
                                                 kCGBitmapByteOrderDefault | kCGImageAlphaPremultipliedFirst);
    CGColorSpaceRelease(colorSpace);
    if (!context) return nil;
    
    CGContextSetShouldAntialias(context, true);
    CGContextSetAllowsAntialiasing(context, true);
    CGContextSetInterpolationQuality(context, kCGInterpolationHigh);
    
    CGContextTranslateCTM(context, +(newRect.size.width * 0.5), +(newRect.size.height * 0.5));
    CGContextRotateCTM(context, radians);
    
    CGContextDrawImage(context, CGRectMake(-(width * 0.5), -(height * 0.5), width, height), self.CGImage);
    CGImageRef imgRef = CGBitmapContextCreateImage(context);
    UIImage *img = [UIImage imageWithCGImage:imgRef scale:self.scale orientation:self.imageOrientation];
    CGImageRelease(imgRef);
    CGContextRelease(context);
    return img;
}

- (UIImage *)_yy_flipHorizontal:(BOOL)horizontal vertical:(BOOL)vertical {
    if (!self.CGImage) return nil;
    size_t width = (size_t)CGImageGetWidth(self.CGImage);
    size_t height = (size_t)CGImageGetHeight(self.CGImage);
    size_t bytesPerRow = width * 4;
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(NULL, width, height, 8, bytesPerRow, colorSpace, kCGBitmapByteOrderDefault | kCGImageAlphaPremultipliedFirst);
    CGColorSpaceRelease(colorSpace);
    if (!context) return nil;
    
    CGContextDrawImage(context, CGRectMake(0, 0, width, height), self.CGImage);
    UInt8 *data = (UInt8 *)CGBitmapContextGetData(context);
    if (!data) {
        CGContextRelease(context);
        return nil;
    }
    vImage_Buffer src = { data, height, width, bytesPerRow };
    vImage_Buffer dest = { data, height, width, bytesPerRow };
    if (vertical) {
        vImageVerticalReflect_ARGB8888(&src, &dest, kvImageBackgroundColorFill);
    }
    if (horizontal) {
        vImageHorizontalReflect_ARGB8888(&src, &dest, kvImageBackgroundColorFill);
    }
    CGImageRef imgRef = CGBitmapContextCreateImage(context);
    CGContextRelease(context);
    UIImage *img = [UIImage imageWithCGImage:imgRef scale:self.scale orientation:self.imageOrientation];
    CGImageRelease(imgRef);
    return img;
}

- (UIImage *)yy_imageByRotateLeft90 {
    return [self yy_imageByRotate:_DegreesToRadians(90) fitSize:YES];
}

- (UIImage *)yy_imageByRotateRight90 {
    return [self yy_imageByRotate:_DegreesToRadians(-90) fitSize:YES];
}

- (UIImage *)yy_imageByRotate180 {
    return [self _yy_flipHorizontal:YES vertical:YES];
}

- (UIImage *)yy_imageByFlipVertical {
    return [self _yy_flipHorizontal:NO vertical:YES];
}

- (UIImage *)yy_imageByFlipHorizontal {
    return [self _yy_flipHorizontal:YES vertical:NO];
}

- (UIImage *)yy_imageByTintColor:(UIColor *)color {
    UIGraphicsBeginImageContextWithOptions(self.size, NO, self.scale);
    CGRect rect = CGRectMake(0, 0, self.size.width, self.size.height);
    [color set];
    UIRectFill(rect);
    [self drawAtPoint:CGPointMake(0, 0) blendMode:kCGBlendModeDestinationIn alpha:1];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;
}

- (UIImage *)yy_imageByGrayscale {
    return [self yy_imageByBlurRadius:0 tintColor:nil tintMode:0 saturation:0 maskImage:nil];
}

- (UIImage *)yy_imageByBlurSoft {
    return [self yy_imageByBlurRadius:60 tintColor:[UIColor colorWithWhite:0.84 alpha:0.36] tintMode:kCGBlendModeNormal saturation:1.8 maskImage:nil];
}

- (UIImage *)yy_imageByBlurLight {
    return [self yy_imageByBlurRadius:60 tintColor:[UIColor colorWithWhite:1.0 alpha:0.3] tintMode:kCGBlendModeNormal saturation:1.8 maskImage:nil];
}

- (UIImage *)yy_imageByBlurExtraLight {
    return [self yy_imageByBlurRadius:40 tintColor:[UIColor colorWithWhite:0.97 alpha:0.82] tintMode:kCGBlendModeNormal saturation:1.8 maskImage:nil];
}

- (UIImage *)yy_imageByBlurDark {
    return [self yy_imageByBlurRadius:40 tintColor:[UIColor colorWithWhite:0.11 alpha:0.73] tintMode:kCGBlendModeNormal saturation:1.8 maskImage:nil];
}

- (UIImage *)yy_imageByBlurWithTint:(UIColor *)tintColor {
    const CGFloat EffectColorAlpha = 0.6;
    UIColor *effectColor = tintColor;
    size_t componentCount = CGColorGetNumberOfComponents(tintColor.CGColor);
    if (componentCount == 2) {
        CGFloat b;
        if ([tintColor getWhite:&b alpha:NULL]) {
            effectColor = [UIColor colorWithWhite:b alpha:EffectColorAlpha];
        }
    } else {
        CGFloat r, g, b;
        if ([tintColor getRed:&r green:&g blue:&b alpha:NULL]) {
            effectColor = [UIColor colorWithRed:r green:g blue:b alpha:EffectColorAlpha];
        }
    }
    return [self yy_imageByBlurRadius:20 tintColor:effectColor tintMode:kCGBlendModeNormal saturation:-1.0 maskImage:nil];
}

- (UIImage *)yy_imageByBlurRadius:(CGFloat)blurRadius
                        tintColor:(UIColor *)tintColor
                         tintMode:(CGBlendMode)tintBlendMode
                       saturation:(CGFloat)saturation
                        maskImage:(UIImage *)maskImage {
    if (self.size.width < 1 || self.size.height < 1) {
        NSLog(@"UIImage+YYAdd error: invalid size: (%.2f x %.2f). Both dimensions must be >= 1: %@", self.size.width, self.size.height, self);
        return nil;
    }
    if (!self.CGImage) {
        NSLog(@"UIImage+YYAdd error: inputImage must be backed by a CGImage: %@", self);
        return nil;
    }
    if (maskImage && !maskImage.CGImage) {
        NSLog(@"UIImage+YYAdd error: effectMaskImage must be backed by a CGImage: %@", maskImage);
        return nil;
    }
    
    // iOS7 and above can use new func.
    BOOL hasNewFunc = (long)vImageBuffer_InitWithCGImage != 0 && (long)vImageCreateCGImageFromBuffer != 0;
    BOOL hasBlur = blurRadius > __FLT_EPSILON__;
    BOOL hasSaturation = fabs(saturation - 1.0) > __FLT_EPSILON__;
    
    CGSize size = self.size;
    CGRect rect = { CGPointZero, size };
    CGFloat scale = self.scale;
    CGImageRef imageRef = self.CGImage;
    BOOL opaque = NO;
    
    if (!hasBlur && !hasSaturation) {
        return [self _yy_mergeImageRef:imageRef tintColor:tintColor tintBlendMode:tintBlendMode maskImage:maskImage opaque:opaque];
    }
    
    vImage_Buffer effect = { 0 }, scratch = { 0 };
    vImage_Buffer *input = NULL, *output = NULL;
    
    vImage_CGImageFormat format = {
        .bitsPerComponent = 8,
        .bitsPerPixel = 32,
        .colorSpace = NULL,
        .bitmapInfo = kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Little, //requests a BGRA buffer.
        .version = 0,
        .decode = NULL,
        .renderingIntent = kCGRenderingIntentDefault
    };
    
    if (hasNewFunc) {
        vImage_Error err;
        err = vImageBuffer_InitWithCGImage(&effect, &format, NULL, imageRef, kvImagePrintDiagnosticsToConsole);
        if (err != kvImageNoError) {
            NSLog(@"UIImage+YYAdd error: vImageBuffer_InitWithCGImage returned error code %zi for inputImage: %@", err, self);
            return nil;
        }
        err = vImageBuffer_Init(&scratch, effect.height, effect.width, format.bitsPerPixel, kvImageNoFlags);
        if (err != kvImageNoError) {
            NSLog(@"UIImage+YYAdd error: vImageBuffer_Init returned error code %zi for inputImage: %@", err, self);
            return nil;
        }
    } else {
        UIGraphicsBeginImageContextWithOptions(size, opaque, scale);
        CGContextRef effectCtx = UIGraphicsGetCurrentContext();
        CGContextScaleCTM(effectCtx, 1.0, -1.0);
        CGContextTranslateCTM(effectCtx, 0, -size.height);
        CGContextDrawImage(effectCtx, rect, imageRef);
        effect.data     = CGBitmapContextGetData(effectCtx);
        effect.width    = CGBitmapContextGetWidth(effectCtx);
        effect.height   = CGBitmapContextGetHeight(effectCtx);
        effect.rowBytes = CGBitmapContextGetBytesPerRow(effectCtx);
        
        UIGraphicsBeginImageContextWithOptions(size, opaque, scale);
        CGContextRef scratchCtx = UIGraphicsGetCurrentContext();
        scratch.data     = CGBitmapContextGetData(scratchCtx);
        scratch.width    = CGBitmapContextGetWidth(scratchCtx);
        scratch.height   = CGBitmapContextGetHeight(scratchCtx);
        scratch.rowBytes = CGBitmapContextGetBytesPerRow(scratchCtx);
    }
    
    input = &effect;
    output = &scratch;
    
    if (hasBlur) {
        // A description of how to compute the box kernel width from the Gaussian
        // radius (aka standard deviation) appears in the SVG spec:
        // http://www.w3.org/TR/SVG/filters.html#feGaussianBlurElement
        //
        // For larger values of 's' (s >= 2.0), an approximation can be used: Three
        // successive box-blurs build a piece-wise quadratic convolution kernel, which
        // approximates the Gaussian kernel to within roughly 3%.
        //
        // let d = floor(s * 3*sqrt(2*pi)/4 + 0.5)
        //
        // ... if d is odd, use three box-blurs of size 'd', centered on the output pixel.
        //
        CGFloat inputRadius = blurRadius * scale;
        if (inputRadius - 2.0 < __FLT_EPSILON__) inputRadius = 2.0;
        uint32_t radius = floor((inputRadius * 3.0 * sqrt(2 * M_PI) / 4 + 0.5) / 2);
        radius |= 1; // force radius to be odd so that the three box-blur methodology works.
        int iterations;
        if (blurRadius * scale < 0.5) iterations = 1;
        else if (blurRadius * scale < 1.5) iterations = 2;
        else iterations = 3;
        NSInteger tempSize = vImageBoxConvolve_ARGB8888(input, output, NULL, 0, 0, radius, radius, NULL, kvImageGetTempBufferSize | kvImageEdgeExtend);
        void *temp = malloc(tempSize);
        for (int i = 0; i < iterations; i++) {
            vImageBoxConvolve_ARGB8888(input, output, temp, 0, 0, radius, radius, NULL, kvImageEdgeExtend);
            // swap
            vImage_Buffer *swap_tmp = input;
            input = output;
            output = swap_tmp;
        }
        free(temp);
    }
    
    
    if (hasSaturation) {
        // These values appear in the W3C Filter Effects spec:
        // https://dvcs.w3.org/hg/FXTF/raw-file/default/filters/Publish.html#grayscaleEquivalent
        CGFloat s = saturation;
        CGFloat matrixFloat[] = {
            0.0722 + 0.9278 * s,  0.0722 - 0.0722 * s,  0.0722 - 0.0722 * s,  0,
            0.7152 - 0.7152 * s,  0.7152 + 0.2848 * s,  0.7152 - 0.7152 * s,  0,
            0.2126 - 0.2126 * s,  0.2126 - 0.2126 * s,  0.2126 + 0.7873 * s,  0,
            0,                    0,                    0,                    1,
        };
        const int32_t divisor = 256;
        NSUInteger matrixSize = sizeof(matrixFloat) / sizeof(matrixFloat[0]);
        int16_t matrix[matrixSize];
        for (NSUInteger i = 0; i < matrixSize; ++i) {
            matrix[i] = (int16_t)roundf(matrixFloat[i] * divisor);
        }
        vImageMatrixMultiply_ARGB8888(input, output, matrix, divisor, NULL, NULL, kvImageNoFlags);
        // swap
        vImage_Buffer *swap_tmp = input;
        input = output;
        output = swap_tmp;
    }
    
    UIImage *outputImage = nil;
    if (hasNewFunc) {
        CGImageRef effectCGImage = NULL;
        effectCGImage = vImageCreateCGImageFromBuffer(input, &format, &_yy_cleanupBuffer, NULL, kvImageNoAllocate, NULL);
        if (effectCGImage == NULL) {
            effectCGImage = vImageCreateCGImageFromBuffer(input, &format, NULL, NULL, kvImageNoFlags, NULL);
            free(input->data);
        }
        free(output->data);
        outputImage = [self _yy_mergeImageRef:effectCGImage tintColor:tintColor tintBlendMode:tintBlendMode maskImage:maskImage opaque:opaque];
        CGImageRelease(effectCGImage);
    } else {
        CGImageRef effectCGImage;
        UIImage *effectImage;
        if (input != &effect) effectImage = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
        if (input == &effect) effectImage = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
        effectCGImage = effectImage.CGImage;
        outputImage = [self _yy_mergeImageRef:effectCGImage tintColor:tintColor tintBlendMode:tintBlendMode maskImage:maskImage opaque:opaque];
    }
    return outputImage;
}

// Helper function to handle deferred cleanup of a buffer.
static void _yy_cleanupBuffer(void *userData, void *buf_data) {
    free(buf_data);
}

// Helper function to add tint and mask.
- (UIImage *)_yy_mergeImageRef:(CGImageRef)effectCGImage
                     tintColor:(UIColor *)tintColor
                 tintBlendMode:(CGBlendMode)tintBlendMode
                     maskImage:(UIImage *)maskImage
                        opaque:(BOOL)opaque {
    BOOL hasTint = tintColor != nil && CGColorGetAlpha(tintColor.CGColor) > __FLT_EPSILON__;
    BOOL hasMask = maskImage != nil;
    CGSize size = self.size;
    CGRect rect = { CGPointZero, size };
    CGFloat scale = self.scale;
    
    if (!hasTint && !hasMask) {
        return [UIImage imageWithCGImage:effectCGImage];
    }
    
    UIGraphicsBeginImageContextWithOptions(size, opaque, scale);
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextScaleCTM(context, 1.0, -1.0);
    CGContextTranslateCTM(context, 0, -size.height);
    if (hasMask) {
        CGContextDrawImage(context, rect, self.CGImage);
        CGContextSaveGState(context);
        CGContextClipToMask(context, rect, maskImage.CGImage);
    }
    CGContextDrawImage(context, rect, effectCGImage);
    if (hasTint) {
        CGContextSaveGState(context);
        CGContextSetBlendMode(context, tintBlendMode);
        CGContextSetFillColorWithColor(context, tintColor.CGColor);
        CGContextFillRect(context, rect);
        CGContextRestoreGState(context);
    }
    if (hasMask) {
        CGContextRestoreGState(context);
    }
    UIImage *outputImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return outputImage;
}

@end