CVPixelBufferRef与UIImage的互相转换

CVPixelBufferRef与UIImage的互相转换
//
// ViewController.m
// test_image_covert_data_01
//
// Created by jeffasd on 2016/9/30.
// Copyright © 2016年 jeffasd. All rights reserved.
//

#import "ViewController.h"

#define RETAINED_BUFFER_COUNT 4

@interface ViewController ()

@property (nonatomic, assign) CVPixelBufferPoolRef pixelBufferPool;

@end

@implementation ViewController

#pragma CVPixelBufferRef与UIImage的互相转换

- (void)viewDidLoad {
[super viewDidLoad];

self.pixelBufferPool = NULL;

UIImage *image = [UIImage imageNamed:@"atlastest"];
CVPixelBufferRef pixelBuffer = [self CVPixelBufferRefFromUiImage:image];
//CVPixelBufferRef pixelBuffer = [self pixelBufferFasterFromImage:image];
//CVPixelBufferRef pixelBuffer = [[self class] pixelBufferFromCGImage:image.CGImage];
//UIImage *covertImage = [[self class] imageFromCVPixelBufferRef0:pixelBuffer];
//UIImage *covertImage = [[self class] imageFromCVPixelBufferRef1:pixelBuffer];
//UIImage *covertImage = [[self class] imageFromCVPixelBufferRef2:pixelBuffer];
// covertImage = nil;
//
UIImage *decodeImage = [[self class] decodeImageWithImage:image];
decodeImage = nil;

CVPixelBufferRef pixelBuffer1 = [self pixelBufferFromImageWithPool:NULL image:image];
pixelBuffer1 = nil;

//covertImage = nil;
}

static OSType inputPixelFormat(){
//注意CVPixelBufferCreate函数不支持 kCVPixelFormatType_32RGBA 等格式 不知道为什么。
//支持kCVPixelFormatType_32ARGB和kCVPixelFormatType_32BGRA等 iPhone为小端对齐因此kCVPixelFormatType_32ARGB和kCVPixelFormatType_32BGRA都需要和kCGBitmapByteOrder32Little配合使用
//注意当inputPixelFormat为kCVPixelFormatType_32BGRA时bitmapInfo不能是kCGImageAlphaNone，kCGImageAlphaLast，kCGImageAlphaFirst，kCGImageAlphaOnly。
//注意iPhone的大小端对齐方式为小段对齐 可以使用宏 kCGBitmapByteOrder32Host 来解决大小端对齐 大小端对齐必须设置为kCGBitmapByteOrder32Little。
//return kCVPixelFormatType_32RGBA;//iPhone不支持此输入格式!!!
return kCVPixelFormatType_32BGRA;
//return kCVPixelFormatType_32ARGB;
}

static uint32_t bitmapInfoWithPixelFormatType(OSType inputPixelFormat){
/*
CGBitmapInfo的设置
uint32_t bitmapInfo = CGImageAlphaInfo | CGBitmapInfo;

当inputPixelFormat=kCVPixelFormatType_32BGRA CGBitmapInfo的正确的设置 只有如下两种正确设置
uint32_t bitmapInfo = kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Host;
uint32_t bitmapInfo = kCGImageAlphaNoneSkipFirst | kCGBitmapByteOrder32Host;

typedef CF_ENUM(uint32_t, CGImageAlphaInfo) {
kCGImageAlphaNone, For example, RGB.
kCGImageAlphaPremultipliedLast, For example, premultiplied RGBA
kCGImageAlphaPremultipliedFirst, For example, premultiplied ARGB
kCGImageAlphaLast, For example, non-premultiplied RGBA
kCGImageAlphaFirst, For example, non-premultiplied ARGB
kCGImageAlphaNoneSkipLast, For example, RBGX.
kCGImageAlphaNoneSkipFirst, For example, XRGB.
kCGImageAlphaOnly No color data, alpha data only
};

当inputPixelFormat=kCVPixelFormatType_32ARGB CGBitmapInfo的正确的设置 只有如下两种正确设置
uint32_t bitmapInfo = kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Big;
uint32_t bitmapInfo = kCGImageAlphaNoneSkipFirst | kCGBitmapByteOrder32Big;
*/
if (inputPixelFormat == kCVPixelFormatType_32BGRA) {
//uint32_t bitmapInfo = kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Host;
//此格式也可以
uint32_t bitmapInfo = kCGImageAlphaNoneSkipFirst | kCGBitmapByteOrder32Host;
return bitmapInfo;
}else if (inputPixelFormat == kCVPixelFormatType_32ARGB){
uint32_t bitmapInfo = kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Big;
//此格式也可以
//uint32_t bitmapInfo = kCGImageAlphaNoneSkipFirst | kCGBitmapByteOrder32Big;
return bitmapInfo;
}else{
NSLog(@"不支持此格式");
return 0;
}
}

static CVPixelBufferPoolRef createPixelBufferPoolInner( int32_t width, int32_t height, OSType pixelFormat, int32_t maxBufferCount )
{
CVPixelBufferPoolRef outputPool = NULL;

NSDictionary *sourcePixelBufferOptions = @{ (id)kCVPixelBufferPixelFormatTypeKey : @(pixelFormat),
(id)kCVPixelBufferWidthKey : @(width),
(id)kCVPixelBufferHeightKey : @(height),
//(id)kCVPixelFormatOpenGLESCompatibility : @(YES),
(id)kCVPixelBufferIOSurfacePropertiesKey : @{ /*empty dictionary*/ } };

NSDictionary *pixelBufferPoolOptions = @{ (id)kCVPixelBufferPoolMinimumBufferCountKey : @(maxBufferCount) };

CVPixelBufferPoolCreate( kCFAllocatorDefault, (__bridge CFDictionaryRef)pixelBufferPoolOptions, (__bridge CFDictionaryRef)sourcePixelBufferOptions, &outputPool );

return outputPool;
}

static CVPixelBufferPoolRef createCVPixelBufferPoolRef(int32_t imageWidth, int32_t imageHeight){
OSType pixelFormat = inputPixelFormat();
int32_t maxRetainedBufferCount = RETAINED_BUFFER_COUNT;
CVPixelBufferPoolRef bufferPool = createPixelBufferPoolInner( imageWidth, imageHeight, pixelFormat, maxRetainedBufferCount );
if ( ! bufferPool ) {
NSLog( @"Problem initializing a buffer pool." );
}
NSLog( @"success initializing a buffer pool." );
return bufferPool;
}

- (CVPixelBufferRef)pixelBufferFromImageWithPool:(CVPixelBufferPoolRef)pixelBufferPool image:(UIImage *)image
{
CVPixelBufferRef pxbuffer = NULL;

NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithBool:YES], kCVPixelBufferCGImageCompatibilityKey,
[NSNumber numberWithBool:YES], kCVPixelBufferCGBitmapContextCompatibilityKey,
nil];

size_t width = CGImageGetWidth(image.CGImage);
size_t height = CGImageGetHeight(image.CGImage);
size_t bytesPerRow = CGImageGetBytesPerRow(image.CGImage);
#if 0
CGBitmapInfo bitmapInfo = CGImageGetBitmapInfo(image.CGImage);
#endif
void *pxdata = NULL;

if (pixelBufferPool == NULL){
NSLog(@"pixelBufferPool is null!");
CVPixelBufferPoolRef bufferPool = createCVPixelBufferPoolRef((int32_t)width, (int32_t)height);
self.pixelBufferPool = bufferPool;
pixelBufferPool = bufferPool;
}

CVReturn status = CVPixelBufferPoolCreatePixelBuffer (NULL, pixelBufferPool, &pxbuffer);
if (pxbuffer == NULL) {
status = CVPixelBufferCreate(kCFAllocatorDefault, width,
height, inputPixelFormat(), (__bridge CFDictionaryRef) options,
&pxbuffer);
}

NSParameterAssert(status == kCVReturnSuccess && pxbuffer != NULL);
CVPixelBufferLockBaseAddress(pxbuffer, 0);
pxdata = CVPixelBufferGetBaseAddress(pxbuffer);
NSParameterAssert(pxdata != NULL);

#if 1 - 此去掉alpha通道效率更高
CGColorSpaceRef rgbColorSpace = CGColorSpaceCreateDeviceRGB();

CGBitmapInfo bitmapInfo = kCGBitmapByteOrder32Host;

//对于生成CVPixelBufferRef无法使用此方法但是对于解码图片可以使用此方法
// CGImageAlphaInfo alphaInfo = CGImageGetAlphaInfo(image.CGImage);
// if (alphaInfo == kCGImageAlphaNone || alphaInfo == kCGImageAlphaOnly) {
// alphaInfo = kCGImageAlphaNoneSkipFirst;
// } else if (alphaInfo == kCGImageAlphaFirst) {
// alphaInfo = kCGImageAlphaPremultipliedFirst;
// } else if (alphaInfo == kCGImageAlphaLast) {
// alphaInfo = kCGImageAlphaPremultipliedLast;
// }
// bitmapInfo |= alphaInfo;

bitmapInfo = bitmapInfoWithPixelFormatType(inputPixelFormat());

size_t bitsPerComponent = CGImageGetBitsPerComponent(image.CGImage);

CGContextRef context = CGBitmapContextCreate(pxdata, width,
height,bitsPerComponent,bytesPerRow, rgbColorSpace,
bitmapInfo);
NSParameterAssert(context);
CGContextConcatCTM(context, CGAffineTransformMakeRotation(0));
CGContextDrawImage(context, CGRectMake(0, 0, width,height), image.CGImage);
CGColorSpaceRelease(rgbColorSpace);
CGContextRelease(context);
#else //- 此方法获取的图片可能无法还原真实的图片
CFDataRef dataFromImageDataProvider = CGDataProviderCopyData(CGImageGetDataProvider(image.CGImage));
GLubyte *imageData = (GLubyte *)CFDataGetBytePtr(dataFromImageDataProvider);
#if 0
CFIndex length = CFDataGetLength(dataFromImageDataProvider);
memcpy(pxdata,imageData,length);
#else
CVPixelBufferCreateWithBytes(kCFAllocatorDefault,width,height,inputPixelFormat(),imageData,bytesPerRow,NULL,NULL,(__bridge CFDictionaryRef)options,&pxbuffer);
#endif
CFRelease(dataFromImageDataProvider);
#endif

return pxbuffer;
}

/** UIImage covert to CVPixelBufferRef */
//方法1 此方法能还原真实的图片
- (CVPixelBufferRef)CVPixelBufferRefFromUiImage:(UIImage *)img {
CGSize size = img.size;
CGImageRef image = [img CGImage];

NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithBool:YES], kCVPixelBufferCGImageCompatibilityKey,
[NSNumber numberWithBool:YES], kCVPixelBufferCGBitmapContextCompatibilityKey, nil];
CVPixelBufferRef pxbuffer = NULL;
CVReturn status = CVPixelBufferCreate(kCFAllocatorDefault, size.width, size.height, inputPixelFormat(), (__bridge CFDictionaryRef) options, &pxbuffer);

NSParameterAssert(status == kCVReturnSuccess && pxbuffer != NULL);

CVPixelBufferLockBaseAddress(pxbuffer, 0);
void *pxdata = CVPixelBufferGetBaseAddress(pxbuffer);
NSParameterAssert(pxdata != NULL);

CGColorSpaceRef rgbColorSpace = CGColorSpaceCreateDeviceRGB();

//CGBitmapInfo的设置
//uint32_t bitmapInfo = CGImageAlphaInfo | CGBitmapInfo;

//当inputPixelFormat=kCVPixelFormatType_32BGRA CGBitmapInfo的正确的设置
//uint32_t bitmapInfo = kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Host;
//uint32_t bitmapInfo = kCGImageAlphaNoneSkipFirst | kCGBitmapByteOrder32Host;

//当inputPixelFormat=kCVPixelFormatType_32ARGB CGBitmapInfo的正确的设置
//uint32_t bitmapInfo = kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Big;
//uint32_t bitmapInfo = kCGImageAlphaNoneSkipFirst | kCGBitmapByteOrder32Big;

uint32_t bitmapInfo = bitmapInfoWithPixelFormatType(inputPixelFormat());

CGContextRef context = CGBitmapContextCreate(pxdata, size.width, size.height, 8, 4*size.width, rgbColorSpace, bitmapInfo);
NSParameterAssert(context);

CGContextDrawImage(context, CGRectMake(0, 0, CGImageGetWidth(image), CGImageGetHeight(image)), image);
CVPixelBufferUnlockBaseAddress(pxbuffer, 0);

CGColorSpaceRelease(rgbColorSpace);
CGContextRelease(context);

return pxbuffer;
}

/** UIImage covert to CVPixelBufferRef */
//方法2 注意此方法在处理某些图片时可能无法还原真实的图片
- (CVPixelBufferRef)pixelBufferFasterFromImage:(UIImage *)image{

CVPixelBufferRef pxbuffer = NULL;
NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithBool:YES], kCVPixelBufferCGImageCompatibilityKey,
[NSNumber numberWithBool:YES], kCVPixelBufferCGBitmapContextCompatibilityKey,
nil];

size_t width = CGImageGetWidth(image.CGImage);
size_t height = CGImageGetHeight(image.CGImage);
size_t bytesPerRow = CGImageGetBytesPerRow(image.CGImage);

CFDataRef dataFromImageDataProvider = CGDataProviderCopyData(CGImageGetDataProvider(image.CGImage));
GLubyte *imageData = (GLubyte *)CFDataGetBytePtr(dataFromImageDataProvider);

//kCGImageAlphaNoneSkipLast, /* For example, RBGX. */

CGColorSpaceRef colorspace = CGImageGetColorSpace(image.CGImage);
CGImageAlphaInfo alphainfo = CGImageGetAlphaInfo(image.CGImage);
CGBitmapInfo bitmapInfo = CGImageGetBitmapInfo(image.CGImage);
const CGFloat *decode = CGImageGetDecode(image.CGImage);
NSString *str = CGImageGetUTType(image.CGImage);

// kCVPixelFormatType_32ARGB = 0x00000020, /* 32 bit ARGB */
// kCVPixelFormatType_32BGRA = 'BGRA', /* 32 bit BGRA */
// kCVPixelFormatType_32ABGR = 'ABGR', /* 32 bit ABGR */不能使用
// kCVPixelFormatType_32RGBA = 'RGBA', /* 32 bit RGBA */不能使用

//CVPixelBufferCreateWithBytes这里是很耗时的，要重新创建。
//此方法获取的CVPixelBufferRef不一定正确 如原始图片的CGImageAlphaInfo为kCGImageAlphaNoneSkipLast由于pixelFormatType没有RBGX类型的格式就没法还原原始的图片。
CVPixelBufferCreateWithBytes(kCFAllocatorDefault,width,height,kCVPixelFormatType_32BGRA,imageData,bytesPerRow,NULL,NULL,(__bridge CFDictionaryRef)options,&pxbuffer);
CFRelease(dataFromImageDataProvider);
CVPixelBufferRetain(pxbuffer);

return pxbuffer;
}

+ (CVPixelBufferRef) pixelBufferFromCGImage: (CGImageRef) image
{
CGSize frameSize = CGSizeMake(CGImageGetWidth(image), CGImageGetHeight(image));
NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithBool:NO], kCVPixelBufferCGImageCompatibilityKey,
[NSNumber numberWithBool:NO], kCVPixelBufferCGBitmapContextCompatibilityKey,
nil];
CVPixelBufferRef pxbuffer = NULL;
CVReturn status = CVPixelBufferCreate(kCFAllocatorDefault, frameSize.width,
frameSize.height, kCVPixelFormatType_32BGRA, (__bridge CFDictionaryRef) options,
&pxbuffer);
NSParameterAssert(status == kCVReturnSuccess && pxbuffer != NULL);
CVPixelBufferLockBaseAddress(pxbuffer, 0);
void *pxdata = CVPixelBufferGetBaseAddress(pxbuffer);
CGColorSpaceRef rgbColorSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef context = CGBitmapContextCreate(pxdata, frameSize.width,
frameSize.height, 8, 4*frameSize.width, rgbColorSpace,
kCGBitmapByteOrder32Little | kCGImageAlphaNoneSkipFirst);
CGContextDrawImage(context, CGRectMake(0, 0, CGImageGetWidth(image),
CGImageGetHeight(image)), image);//这个站CPU 相当高
CGColorSpaceRelease(rgbColorSpace);
CGContextRelease(context);
CVPixelBufferUnlockBaseAddress(pxbuffer, 0);
return pxbuffer;
}

//CVPixelBufferRef 是 CMSampleBufferRef 解码后的数据

/** UIImage covert to CMSampleBufferRef */

/** CVPixelBufferRef covert to UIImage */
+ (UIImage *)imageFromCVPixelBufferRef0:(CVPixelBufferRef)pixelBuffer{
// MUST READ-WRITE LOCK THE PIXEL BUFFER!!!!
CVPixelBufferLockBaseAddress(pixelBuffer, 0);
CIImage *ciImage = [CIImage imageWithCVPixelBuffer:pixelBuffer];
CVPixelBufferUnlockBaseAddress(pixelBuffer, 0);
CIContext *temporaryContext = [CIContext contextWithOptions:nil];
CGImageRef videoImage = [temporaryContext
createCGImage:ciImage
fromRect:CGRectMake(0, 0,
CVPixelBufferGetWidth(pixelBuffer),
CVPixelBufferGetHeight(pixelBuffer))];

UIImage *uiImage = [UIImage imageWithCGImage:videoImage];
CGImageRelease(videoImage);
CVPixelBufferRelease(pixelBuffer);
return uiImage;
}

static OSStatus CreateCGImageFromCVPixelBuffer(CVPixelBufferRef pixelBuffer, CGImageRef *imageOut)
{
OSStatus err = noErr;
OSType sourcePixelFormat;
size_t width, height, sourceRowBytes;
void *sourceBaseAddr = NULL;
CGBitmapInfo bitmapInfo;
CGColorSpaceRef colorspace = NULL;
CGDataProviderRef provider = NULL;
CGImageRef image = NULL;
sourcePixelFormat = CVPixelBufferGetPixelFormatType( pixelBuffer );
if ( kCVPixelFormatType_32ARGB == sourcePixelFormat )
bitmapInfo = kCGBitmapByteOrder32Big | kCGImageAlphaNoneSkipFirst;
else if ( kCVPixelFormatType_32BGRA == sourcePixelFormat )
bitmapInfo = kCGBitmapByteOrder32Little | kCGImageAlphaNoneSkipFirst;
else
return -95014; // only uncompressed pixel formats
sourceRowBytes = CVPixelBufferGetBytesPerRow( pixelBuffer );
width = CVPixelBufferGetWidth( pixelBuffer );
height = CVPixelBufferGetHeight( pixelBuffer );
CVPixelBufferLockBaseAddress( pixelBuffer, 0 );
sourceBaseAddr = CVPixelBufferGetBaseAddress( pixelBuffer );
colorspace = CGColorSpaceCreateDeviceRGB();
CVPixelBufferRetain( pixelBuffer );
provider = CGDataProviderCreateWithData( (void *)pixelBuffer, sourceBaseAddr, sourceRowBytes * height, ReleaseCVPixelBuffer);
image = CGImageCreate(width, height, 8, 32, sourceRowBytes, colorspace, bitmapInfo, provider, NULL, true, kCGRenderingIntentDefault);
if ( err && image ) {
CGImageRelease( image );
image = NULL;
}
if ( provider ) CGDataProviderRelease( provider );
if ( colorspace ) CGColorSpaceRelease( colorspace );
*imageOut = image;
return err;
}

static void ReleaseCVPixelBuffer(void *pixel, const void *data, size_t size)
{
CVPixelBufferRef pixelBuffer = (CVPixelBufferRef)pixel;
CVPixelBufferUnlockBaseAddress( pixelBuffer, 0 );
CVPixelBufferRelease( pixelBuffer );
}

+(UIImage *)imageFromCVPixelBufferRef1:(CVPixelBufferRef)pixelBuffer{
UIImage *image;
@autoreleasepool {
CGImageRef cgImage = NULL;
CVPixelBufferRef pb = (CVPixelBufferRef)pixelBuffer;
CVPixelBufferLockBaseAddress(pb, kCVPixelBufferLock_ReadOnly);
OSStatus res = CreateCGImageFromCVPixelBuffer(pb,&cgImage);
if (res == noErr){
image= [UIImage imageWithCGImage:cgImage scale:1.0 orientation:UIImageOrientationUp];
}
CVPixelBufferUnlockBaseAddress(pb, kCVPixelBufferLock_ReadOnly);
CGImageRelease(cgImage);
}
return image;
}
//第二种
+(UIImage *)imageFromCVPixelBufferRef2:(CVPixelBufferRef)pixelBuffer{
CVPixelBufferRef pb = (CVPixelBufferRef)pixelBuffer;
CVPixelBufferLockBaseAddress(pb, kCVPixelBufferLock_ReadOnly);
int w = CVPixelBufferGetWidth(pb);
int h = CVPixelBufferGetHeight(pb);
int r = CVPixelBufferGetBytesPerRow(pb);
int bytesPerPixel = r/w;
unsigned char *buffer = CVPixelBufferGetBaseAddress(pb);
UIGraphicsBeginImageContext(CGSizeMake(w, h));
CGContextRef c = UIGraphicsGetCurrentContext();
unsigned char *data = CGBitmapContextGetData(c);
if (data != NULL) {
int maxY = h;
for(int y = 0; y<maxY; y++) {
for(int x = 0; x<w; x++) {
int offset = bytesPerPixel*((w*y)+x);
data[offset] = buffer[offset]; // R
data[offset+1] = buffer[offset+1]; // G
data[offset+2] = buffer[offset+2]; // B
data[offset+3] = buffer[offset+3]; // A
}
}
}
UIImage *img = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
CVPixelBufferUnlockBaseAddress(pb, kCVPixelBufferLock_ReadOnly);
return img;
}

/** CMSampleBufferRef covert to UIImage */

/** CMSampleBufferRef covert to CVPixelBufferRef */

/** decode compress image to bitmap iamge */
+ (UIImage *)decodeImageWithImage:(UIImage *)imageToPredraw
{
// Always use a device RGB color space for simplicity and predictability what will be going on.
CGColorSpaceRef colorSpaceDeviceRGBRef = CGColorSpaceCreateDeviceRGB();
// Early return on failure!
if (!colorSpaceDeviceRGBRef) {
NSLog(@"Failed to `CGColorSpaceCreateDeviceRGB` for image %@", imageToPredraw);
return imageToPredraw;
}

// "In iOS 4.0 and later, and OS X v10.6 and later, you can pass NULL if you want Quartz to allocate memory for the bitmap." (source: docs)
void *data = NULL;
size_t width = imageToPredraw.size.width;
size_t height = imageToPredraw.size.height;
size_t bitsPerComponent = CHAR_BIT;//一个像素的单个组成部分的位数 如RGBA 此值指定R,G,B,A,每个分量占的位数为8bit。

#if 1
// Even when the image doesn't have transparency, we have to add the extra channel because Quartz doesn't support other pixel formats than 32 bpp/8 bpc for RGB:
// kCGImageAlphaNoneSkipFirst, kCGImageAlphaNoneSkipLast, kCGImageAlphaPremultipliedFirst, kCGImageAlphaPremultipliedLast
// (source: docs "Quartz 2D Programming Guide > Graphics Contexts > Table 2-1 Pixel formats supported for bitmap graphics contexts")
size_t numberOfComponents = CGColorSpaceGetNumberOfComponents(colorSpaceDeviceRGBRef) + 1; // 4: RGB + A
size_t bitsPerPixel = (bitsPerComponent * numberOfComponents);//一个像素点占用的位数 如RGBA=8*4
size_t bytesPerPixel = (bitsPerPixel / BYTE_SIZE);//一个像素点占用的字节数
size_t bytesPerRow = (bytesPerPixel * width);//一行的全部像素占用的字节数
#else
size_t bytesPerRow = 0;//对于CGBitmapContextCreate函数当bytesPerRow=0系统不仅会为我们自动计算，而且还会进行 cache line alignment 的优化
#endif

CGBitmapInfo bitmapInfo = kCGBitmapByteOrder32Host;

CGImageAlphaInfo alphaInfo = CGImageGetAlphaInfo(imageToPredraw.CGImage);
// If the alpha info doesn't match to one of the supported formats (see above), pick a reasonable supported one.
// "For bitmaps created in iOS 3.2 and later, the drawing environment uses the premultiplied ARGB format to store the bitmap data." (source: docs)
if (alphaInfo == kCGImageAlphaNone || alphaInfo == kCGImageAlphaOnly) {
alphaInfo = kCGImageAlphaNoneSkipFirst;
} else if (alphaInfo == kCGImageAlphaFirst) {
alphaInfo = kCGImageAlphaPremultipliedFirst;
} else if (alphaInfo == kCGImageAlphaLast) {
alphaInfo = kCGImageAlphaPremultipliedLast;
}
// "The constants for specifying the alpha channel information are declared with the `CGImageAlphaInfo` type but can be passed to this parameter safely." (source: docs)
bitmapInfo |= alphaInfo;

// Create our own graphics context to draw to; `UIGraphicsGetCurrentContext`/`UIGraphicsBeginImageContextWithOptions` doesn't create a new context but returns the current one which isn't thread-safe (e.g. main thread could use it at the same time).
// Note: It's not worth caching the bitmap context for multiple frames ("unique key" would be `width`, `height` and `hasAlpha`), it's ~50% slower. Time spent in libRIP's `CGSBlendBGRA8888toARGB8888` suddenly shoots up -- not sure why.
//data为NULL系统自动分配内存空间
CGContextRef bitmapContextRef = CGBitmapContextCreate(data, width, height, bitsPerComponent, bytesPerRow, colorSpaceDeviceRGBRef, bitmapInfo);
CGColorSpaceRelease(colorSpaceDeviceRGBRef);
// Early return on failure!
if (!bitmapContextRef) {
NSLog(@"Failed to `CGBitmapContextCreate` with color space %@ and parameters (width: %zu height: %zu bitsPerComponent: %zu bytesPerRow: %zu) for image %@", colorSpaceDeviceRGBRef, width, height, bitsPerComponent, bytesPerRow, imageToPredraw);
return imageToPredraw;
}

// Draw image in bitmap context and create image by preserving receiver's properties.
CGContextDrawImage(bitmapContextRef, CGRectMake(0.0, 0.0, imageToPredraw.size.width, imageToPredraw.size.height), imageToPredraw.CGImage);
CGImageRef predrawnImageRef = CGBitmapContextCreateImage(bitmapContextRef);
UIImage *predrawnImage = [UIImage imageWithCGImage:predrawnImageRef scale:imageToPredraw.scale orientation:imageToPredraw.imageOrientation];
CGImageRelease(predrawnImageRef);
CGContextRelease(bitmapContextRef);

// Early return on failure!
if (!predrawnImage) {
NSLog(@"Failed to `imageWithCGImage:scale:orientation:` with image ref %@ created with color space %@ and bitmap context %@ and properties and properties (scale: %f orientation: %ld) for image %@", predrawnImageRef, colorSpaceDeviceRGBRef, bitmapContextRef, imageToPredraw.scale, (long)imageToPredraw.imageOrientation, imageToPredraw);
return imageToPredraw;
}

return predrawnImage;
}

- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}

@end