iOS Example：SquareCam分析

[cpp]
// used for KVO observation of the @"capturingStillImage" property to perform flash bulb animation
static const NSString *AVCaptureStillImageIsCapturingStillImageContext = @"AVCaptureStillImageIsCapturingStillImageContext";

static CGFloat DegreesToRadians(CGFloat degrees) {return degrees * M_PI / 180;};

static void ReleaseCVPixelBuffer(void *pixel, const void *data, size_t size);
static void ReleaseCVPixelBuffer(void *pixel, const void *data, size_t size)
{
    /**
     CVPixelBuffer(core video pixel buffer)：指的是主内存中的图片缓存，用来保存图片像素数据。应用程序在产生图片帧、解压缩视频数据或调用Core Image的时候可以调用此对象
     **/
    CVPixelBufferRef pixelBuffer = (CVPixelBufferRef)pixel;
    CVPixelBufferUnlockBaseAddress( pixelBuffer, 0 );
    CVPixelBufferRelease( pixelBuffer );
}

//用给定的pixel buffer创建CGImage对象， pixel buffer必须为未压缩的kCVPixelFormatType_32ARGB 或者 kCVPixelFormatType_32BGRA
static OSStatus CreateCGImageFromCVPixelBuffer(CVPixelBufferRef pixelBuffer, CGImageRef *imageOut);
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;

    //一些Quartz程序直接提供block数据给程序，而不是从内存中读取，CGDataProviderRef允许用户以这种方式提供给Quartz数据。（等于是Quartz定义的一种数据格式）
    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


    //获取pixel buffer中数据属性
    sourceRowBytes = CVPixelBufferGetBytesPerRow( pixelBuffer );
    width = CVPixelBufferGetWidth( pixelBuffer );
    height = CVPixelBufferGetHeight( pixelBuffer );

    CVPixelBufferLockBaseAddress( pixelBuffer, 0 );

    //获取pixel buffer的其实地址？直接内存操作了啊？靠
    sourceBaseAddr = CVPixelBufferGetBaseAddress( pixelBuffer );

    colorspace = CGColorSpaceCreateDeviceRGB();

    CVPixelBufferRetain( pixelBuffer );

    //将Data转换为Quartz直接访问的数据类型，目测其逻辑为制定数据内容，给定起始地址、长度等信息。
    provider = CGDataProviderCreateWithData( (void *)pixelBuffer, sourceBaseAddr, sourceRowBytes * height, ReleaseCVPixelBuffer);
    image = CGImageCreate(width, height, 8, 32, sourceRowBytes, colorspace, bitmapInfo, provider, NULL, true, kCGRenderingIntentDefault);

bail:
    if ( err && image ) {
        CGImageRelease( image );
        image = NULL;
    }
    if ( provider ) CGDataProviderRelease( provider );
    if ( colorspace ) CGColorSpaceRelease( colorspace );
    *imageOut = image;
    return err;
}

// utility used by newSquareOverlayedImageForFeatures for
static CGContextRef CreateCGBitmapContextForSize(CGSize size);
static CGContextRef CreateCGBitmapContextForSize(CGSize size)
{
    CGContextRef    context = NULL;
    CGColorSpaceRef colorSpace;   //
    int             bitmapBytesPerRow;

    bitmapBytesPerRow = (size.width * 4);

    colorSpace = CGColorSpaceCreateDeviceRGB();
    context = CGBitmapContextCreate (NULL,
                                     size.width,
                                     size.height,
                                     8,      // bits per component
                                     bitmapBytesPerRow,
                                     colorSpace,
                                     kCGImageAlphaPremultipliedLast);
    CGContextSetAllowsAntialiasing(context, NO);
    CGColorSpaceRelease( colorSpace );
    return context;
}

#pragma mark-

@inte易做图ce UIImage (RotationMethods)
- (UIImage *)imageRotatedByDegrees:(CGFloat)degrees;
@end

@implementation UIImage (RotationMethods)

- (UIImage *)imageRotatedByDegrees:(CGFloat)degrees
{
    // calculate the size of the rotated view's containing box for our drawing space &nb

补充：移动开发 , IOS ,