AVCaptureVideoPreviewLayer 相机截屏

很多文章都提到是普通view或者layer的截屏方法，就不再重复

针对特殊的 AVCaptureVideoPreviewLayer写的相机截屏如下

先从视频流获取图片，绘制成图片，再将view绘制上去，这其中view的不能设置背景色，否则相机部分是view的底色

```

-(void)cwCameraCaptureOutputSampleBuffer: (CMSampleBufferRef _Nullable)sampleBuffer bufferType: (NSInteger)bufferType{

    [self stopTimer:_cameraTimer];

    if(isStopLivess == NO){

        UIImage*image = [UIImagecw_getImageFromBGRA:sampleBufferbufferType:bufferType];

        dispatch_async(dispatch_get_main_queue(), ^{

                [self snapScreenImage:image controller:self];

        });

    }

}

- (void)snapScreenImage:(UIImage*)imagecontroller:(UIViewController*)controller

{

    CGSizescreenSize = [[UIScreenmainScreen]bounds].size;

    UIGraphicsBeginImageContextWithOptions([[UIScreen mainScreen] bounds].size, NO, 0);

    CGContextRef context = UIGraphicsGetCurrentContext();

    UIGraphicsPushContext(context);

    CGFloatcameraScale =640/480.0;

    CGFloatcameraViewWidth =_camareView.cameraView.bounds.size.width;

    CGFloatcameraViewHeight =_camareView.cameraView.bounds.size.height;

//    CGFloat preLayerW = cameraViewWidth;

//    CGFloat preLayerH = preLayerW * cameraScale;

//    CGFloat preLayerY = -(preLayerH - cameraViewHeight) * 0.5;

    [image drawInRect:CGRectMake(CGRectGetMinX(_camareView.cameraView.frame), CGRectGetMinY(_camareView.cameraView.frame)-20, cameraViewWidth, image.size.height * cameraViewWidth/ image.size.width)];

    UIGraphicsPopContext();

   [self renderView:_camareView inContext:context];

    UIImage *screenshot = UIGraphicsGetImageFromCurrentImageContext();

    UIImageWriteToSavedPhotosAlbum(screenshot, nil, nil, nil);

    UIGraphicsEndImageContext();

}

- (void)renderView:(UIView*)viewinContext:(CGContextRef)context

{

    // -renderInContext: renders in the coordinate space of the layer,

    // so we must first apply the layer's geometry to the graphics context

    CGContextSaveGState(context);

    // Center the context around the window's anchor point

    CGContextTranslateCTM(context, [view center].x, [view center].y);

    // Apply the window's transform about the anchor point

    CGContextConcatCTM(context, [view transform]);

    // Offset by the portion of the bounds left of and above the anchor point

    CGContextTranslateCTM(context,

                          -[viewbounds].size.width* [[viewlayer]anchorPoint].x,

                          -[viewbounds].size.height* [[viewlayer]anchorPoint].y);

    // Render the layer hierarchy to the current context

    [[viewlayer]renderInContext:context];

//    [view drawViewHierarchyInRect:view.frame afterScreenUpdates:NO];

    // Restore the context

    CGContextRestoreGState(context);

}

```