GPUImage源码解读(十一)

GPUImageStillCamera主要用来进行拍照。它继承自 GPUImageVideoCamera，因此，除了具备GPUImageVideoCamera的功能，它还提供了一套丰富的拍照API，方便我们进行拍照的相关操作。

• 属性列表。GPUImageStillCamera属性比较少，属性也主要是与图片相关

// jpeg图片的压缩率，默认是0.8
@property CGFloat jpegCompressionQuality;
// 图片的Metadata信息
@property (readonly) NSDictionary *currentCaptureMetadata;

• 方法列表。方法主要是和拍照相关，输出的类型比较丰富，可以是CMSampleBuffer、UIImage、NSData 等。如果有滤镜需要，还可以传入相关滤镜（final Filter In Chain）。

- (void)capturePhotoAsSampleBufferWithCompletionHandler:(void (^)(CMSampleBufferRef imageSampleBuffer, NSError *error))block;
- (void)capturePhotoAsImageProcessedUpToFilter:(GPUImageOutput<GPUImageInput> *)finalFilterInChain withCompletionHandler:(void (^)(UIImage *processedImage, NSError *error))block;
- (void)capturePhotoAsImageProcessedUpToFilter:(GPUImageOutput<GPUImageInput> *)finalFilterInChain withOrientation:(UIImageOrientation)orientation withCompletionHandler:(void (^)(UIImage *processedImage, NSError *error))block;
- (void)capturePhotoAsJPEGProcessedUpToFilter:(GPUImageOutput<GPUImageInput> *)finalFilterInChain withCompletionHandler:(void (^)(NSData *processedJPEG, NSError *error))block;
- (void)capturePhotoAsJPEGProcessedUpToFilter:(GPUImageOutput<GPUImageInput> *)finalFilterInChain withOrientation:(UIImageOrientation)orientation withCompletionHandler:(void (^)(NSData *processedJPEG, NSError *error))block;
- (void)capturePhotoAsPNGProcessedUpToFilter:(GPUImageOutput<GPUImageInput> *)finalFilterInChain withCompletionHandler:(void (^)(NSData *processedPNG, NSError *error))block;
- (void)capturePhotoAsPNGProcessedUpToFilter:(GPUImageOutput<GPUImageInput> *)finalFilterInChain withOrientation:(UIImageOrientation)orientation withCompletionHandler:(void (^)(NSData *processedPNG, NSError *error))block;

这些方法最终都会下面这个内部方法

#pragma mark - Private Methods

- (void)capturePhotoProcessedUpToFilter:(GPUImageOutput<GPUImageInput> *)finalFilterInChain withImageOnGPUHandler:(void (^)(NSError *error))block
{

    //dispatch_semaphore_wait等待信号，当信号总量少于0的时候就会一直等待，否则就可以正常的执行，并让信号总量-1
    dispatch_semaphore_wait(frameRenderingSemaphore, DISPATCH_TIME_FOREVER);

    //判断是否捕获图像
    if(photoOutput.isCapturingStillImage){
        block([NSError errorWithDomain:AVFoundationErrorDomain code:AVErrorMaximumStillImageCaptureRequestsExceeded userInfo:nil]);
        return;
    }

    // 异步捕获图像
    [photoOutput captureStillImageAsynchronouslyFromConnection:[[photoOutput connections] objectAtIndex:0] completionHandler:^(CMSampleBufferRef imageSampleBuffer, NSError *error) {
        if(imageSampleBuffer == NULL){
            block(error);
            return;
        }

        // For now, resize photos to fix within the max texture size of the GPU
        CVImageBufferRef cameraFrame = CMSampleBufferGetImageBuffer(imageSampleBuffer);
        // 获取图像大小
        CGSize sizeOfPhoto = CGSizeMake(CVPixelBufferGetWidth(cameraFrame), CVPixelBufferGetHeight(cameraFrame));
        CGSize scaledImageSizeToFitOnGPU = [GPUImageContext sizeThatFitsWithinATextureForSize:sizeOfPhoto];
         // 判断时候需要调整大小
        if (!CGSizeEqualToSize(sizeOfPhoto, scaledImageSizeToFitOnGPU))
        {
            CMSampleBufferRef sampleBuffer = NULL;
            /*
             CVPixelBufferIsPlanar可得到像素的存储方式是Planar或Chunky。若是Planar，则通过CVPixelBufferGetPlaneCount获取YUV Plane数量。通常是两个Plane，Y为一个Plane，UV由VTDecompressionSessionCreate创建解码会话时通过destinationImageBufferAttributes指定需要的像素格式（可不同于视频源像素格式）决定是否同属一个Plane，每个Plane可当作表格按行列处理，像素是行顺序填充的。下面以Planar Buffer存储方式作说明

             */
            if (CVPixelBufferGetPlaneCount(cameraFrame) > 0)
            {
                NSAssert(NO, @"Error: no downsampling for YUV input in the framework yet");
            }
            else
            {
                 // 图像调整
                GPUImageCreateResizedSampleBuffer(cameraFrame, scaledImageSizeToFitOnGPU, &sampleBuffer);
            }

            dispatch_semaphore_signal(frameRenderingSemaphore);
            [finalFilterInChain useNextFrameForImageCapture];
            // 调用父类进行图片处理，生成帧缓存对象
            [self captureOutput:photoOutput didOutputSampleBuffer:sampleBuffer fromConnection:[[photoOutput connections] objectAtIndex:0]];
            dispatch_semaphore_wait(frameRenderingSemaphore, DISPATCH_TIME_FOREVER);
            if (sampleBuffer != NULL)
                CFRelease(sampleBuffer);
        }
        else
        {
            // This is a workaround for the corrupt images that are sometimes returned when taking a photo with the front camera and using the iOS 5.0 texture caches
            AVCaptureDevicePosition currentCameraPosition = [[videoInput device] position];
            if ( (currentCameraPosition != AVCaptureDevicePositionFront) || (![GPUImageContext supportsFastTextureUpload]) || !requiresFrontCameraTextureCacheCorruptionWorkaround)
            {
                dispatch_semaphore_signal(frameRenderingSemaphore);
                [finalFilterInChain useNextFrameForImageCapture];
                // 调用父类进行图片处理，生成帧缓存对象
                [self captureOutput:photoOutput didOutputSampleBuffer:imageSampleBuffer fromConnection:[[photoOutput connections] objectAtIndex:0]];
                dispatch_semaphore_wait(frameRenderingSemaphore, DISPATCH_TIME_FOREVER);
            }
        }
        //图片的metadate 信息
        CFDictionaryRef metadata = CMCopyDictionaryOfAttachments(NULL, imageSampleBuffer, kCMAttachmentMode_ShouldPropagate);
        _currentCaptureMetadata = (__bridge_transfer NSDictionary *)metadata;

        block(nil);

        _currentCaptureMetadata = nil;
    }];
}