用AVCaptureSession捕获视频，用EAGLContext没有可见输出

Question

我正在用iPhone上的后摄像头用AVCaptureSession捕捉实时视频，用CoreImage应用一些过滤器，然后尝试用OpenGL ES输出最终的视频。大部分代码来自WWDC 2012会话“核心图像技术”的一个示例。

使用UIImage imageWithCIImage显示过滤器链的输出：.或者为每个帧创建一个CGImageRef可以很好地工作。然而，当我试图用OpenGL显示时，我得到的只是一个黑色的屏幕。

在本课程中，他们使用自定义视图类来显示输出，但是该类的代码不可用。我的视图控制器类扩展了GLKViewController，它的视图类被设置为GLKView。

我已经搜索并下载了我能找到的所有GLKit教程和示例，但是没有任何帮助。特别是，当我试图从这里运行这个示例时，也无法获得任何视频输出。谁能给我指明正确的方向？

#import "VideoViewController.h"

@interface VideoViewController ()
{
    AVCaptureSession *_session;

    EAGLContext *_eaglContext;
    CIContext *_ciContext;

    CIFilter *_sepia;
    CIFilter *_bumpDistortion;
}

- (void)setupCamera;
- (void)setupFilters;

@end

@implementation VideoViewController

- (void)viewDidLoad
{
    [super viewDidLoad];

    GLKView *view = (GLKView *)self.view;

    _eaglContext = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES3];
    [EAGLContext setCurrentContext:_eaglContext];

    view.context = _eaglContext;

    // Configure renderbuffers created by the view
    view.drawableColorFormat = GLKViewDrawableColorFormatRGBA8888;
    view.drawableDepthFormat = GLKViewDrawableDepthFormat24;
    view.drawableStencilFormat = GLKViewDrawableStencilFormat8;

    [self setupCamera];
    [self setupFilters];
}

- (void)setupCamera {
    _session = [AVCaptureSession new];
    [_session beginConfiguration];

    [_session setSessionPreset:AVCaptureSessionPreset640x480];

    AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
    AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:device error:nil];
    [_session addInput:input];

    AVCaptureVideoDataOutput *dataOutput = [AVCaptureVideoDataOutput new];
    [dataOutput setAlwaysDiscardsLateVideoFrames:YES];

    NSDictionary *options;
    options = @{ (id)kCVPixelBufferPixelFormatTypeKey : [NSNumber numberWithInt:kCVPixelFormatType_420YpCbCr8BiPlanarFullRange] };

    [dataOutput setVideoSettings:options];

    [dataOutput setSampleBufferDelegate:self queue:dispatch_get_main_queue()];

    [_session addOutput:dataOutput];
    [_session commitConfiguration];
}

#pragma mark Setup Filters
- (void)setupFilters {
    _sepia = [CIFilter filterWithName:@"CISepiaTone"];
    [_sepia setValue:@0.7 forKey:@"inputIntensity"];

    _bumpDistortion = [CIFilter filterWithName:@"CIBumpDistortion"];
    [_bumpDistortion setValue:[CIVector vectorWithX:240 Y:320] forKey:@"inputCenter"];
    [_bumpDistortion setValue:[NSNumber numberWithFloat:200] forKey:@"inputRadius"];
    [_bumpDistortion setValue:[NSNumber numberWithFloat:3.0] forKey:@"inputScale"];
}

#pragma mark Main Loop
- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection {
    // Grab the pixel buffer
    CVPixelBufferRef pixelBuffer = (CVPixelBufferRef)CMSampleBufferGetImageBuffer(sampleBuffer);

    // null colorspace to avoid colormatching
    NSDictionary *options = @{ (id)kCIImageColorSpace : (id)kCFNull };
    CIImage *image = [CIImage imageWithCVPixelBuffer:pixelBuffer options:options];

    image = [image imageByApplyingTransform:CGAffineTransformMakeRotation(-M_PI/2.0)];
    CGPoint origin = [image extent].origin;
    image = [image imageByApplyingTransform:CGAffineTransformMakeTranslation(-origin.x, -origin.y)];

    // Pass it through the filter chain
    [_sepia setValue:image forKey:@"inputImage"];
    [_bumpDistortion setValue:_sepia.outputImage forKey:@"inputImage"];

    // Grab the final output image
    image = _bumpDistortion.outputImage;

    // draw to GLES context
    [_ciContext drawImage:image inRect:CGRectMake(0, 0, 480, 640) fromRect:[image extent]];

    // and present to screen
    [_eaglContext presentRenderbuffer:GL_RENDERBUFFER];

    NSLog(@"frame hatched");

    [_sepia setValue:nil forKey:@"inputImage"];
}

- (void)loadView {
    [super loadView];

    // Initialize the CIContext with a null working space
    NSDictionary *options = @{ (id)kCIContextWorkingColorSpace : (id)kCFNull };
    _ciContext = [CIContext contextWithEAGLContext:_eaglContext options:options];
}

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];

    [_session startRunning];
}

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

@end

Answer 1

哇，其实是我自己想出来的。(这一行工作终究适合我;)

首先，无论出于什么原因，这段代码只适用于OpenGL ES 2，而不是3。

其次，我在loadView方法中设置了loadView，该方法显然在viewDidLoad方法之前运行，因此使用尚未初始化的EAGLContext。