GPUImage的基本用法

建议CocoaPods导入GPUImage类库，引入头文件即可使用:
#import "GPUImage.h"

视频实时滤镜

_stillCamera = [[GPUImageStillCamera alloc] initWithSessionPreset:AVCaptureSessionPreset640x480 cameraPosition:AVCaptureDevicePositionBack];
_stillCamera.outputImageOrientation = UIInterfaceOrientationPortrait;
_stillCamera.frameRate = 30;
_stillCamera.horizontallyMirrorFrontFacingCamera = NO;
_filter = [[GPUImageBrightnessFilter alloc] init];
_filter.brightness=0.0;
GPUImageView *filteredVideoView = [[GPUImageView alloc] initWithFrame:CGRectMake(0.0, 0.0, viewWidth, viewHeight)];
filteredVideoView.fillMode =kGPUImageFillModePreserveAspectRatioAndFill;
[self.view insertSubview:filteredVideoView atIndex:0];
/*
 *视频实时滤镜（从camera获取经过_filter显示到filteredVideoView）
 */
[_stillCamera addTarget:_filter];
[_filter addTarget:filteredVideoView];

视频的写入

/*
 *moveWriter用来记录保存视频
 */
NSString *pathToMovie = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents/Movie.m4v"];
unlink([pathToMovie UTF8String]);
self.movieURL = [NSURL fileURLWithPath:pathToMovie];
self.moveWriter =[[GPUImageMovieWriter alloc] initWithMovieURL:self.movieURL size:CGSizeMake(640.0, 480.0)];
[_filter addTarget:self.moveWriter];                    //（经过_filter传给moveWriter）
self.moveWriter.encodingLiveVideo = YES;
_stillCamera.audioEncodingTarget = _moveWriter;         //_moveWriter处理音频流
    
[_stillCamera startCameraCapture];                      //开始捕获画面

图片捕获与过滤

[_stillCamera capturePhotoAsImageProcessedUpToFilter:_filter withCompletionHandler:^(UIImage *processedImage, NSError *error) {
    NSData *dataForJPEGFile = UIImageJPEGRepresentation(processedImage, 0.8);
    UIImage *image=[[UIImage alloc]initWithData:dataForJPEGFile];
    //保存到沙盒document下
//    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
//    NSString *documentsDirectory = [paths objectAtIndex:0];
//    NSError *error2 = nil;
//    if (![dataForJPEGFile writeToFile:[documentsDirectory stringByAppendingPathComponent:@"FilteredPhoto.jpg"] options:NSAtomicWrite error:&error2])
//    {
//         return;
//    }
        
    //保存到相册
//    __block NSString *createdAssetID =nil;//唯一标识，可以用于图片资源获取
//    NSError *myError =nil;
//    [[PHPhotoLibrary sharedPhotoLibrary]performChangesAndWait:^{
//    createdAssetID = [PHAssetChangeRequest creationRequestForAssetFromImage:image].placeholderForCreatedAsset.localIdentifier;
//    } error:&myError];
    self.photoImage=image;
    self.type=ShowTypeImage;
    [self performSegueWithIdentifier:@"show" sender:nil];
 }];

图片滤镜

- (UIImage *)applyFilter:(GPUImageFilter *)filter
{
    /*
     *滤镜一张图片
     */
    [filter forceProcessingAtSize:self.imageView.image.size];
    [_pic removeAllTargets];
    [_pic addTarget:filter];
    [_pic processImage];
    [filter useNextFrameForImageCapture];
    return [filter imageFromCurrentFramebuffer];
}
//假若只需要对一张图片进行单一滤镜的话，可以这样写：
GPUImageSepiaFilter *stillImageFilter2 = [[GPUImageSepiaFilter alloc] init];
UIImage *quickFilteredImage = [stillImageFilter2 imageByFilteringImage:inputImage];

本地视频滤镜及保存

movieFile = [[GPUImageMovie alloc] initWithURL:sampleURL];
pixellateFilter = [[GPUImagePixellateFilter alloc] init];
[movieFile addTarget:pixellateFilter];
NSString *pathToMovie = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents/Movie.m4v"];
unlink([pathToMovie UTF8String]);
NSURL *movieURL = [NSURL fileURLWithPath:pathToMovie];
movieWriter = [[GPUImageMovieWriter alloc] initWithMovieURL:movieURL size:CGSizeMake(480.0, 640.0)];
[pixellateFilter addTarget:movieWriter];
movieWriter.shouldPassthroughAudio = YES;
movieFile.audioEncodingTarget = movieWriter;
[movieFile enableSynchronizedEncodingUsingMovieWriter:movieWriter];
[movieWriter startRecording];
[movieFile startProcessing];``
//记录结束时，需要把movieWriter从滤镜中移除，并且关闭它：
[pixellateFilter removeTarget:movieWriter];
[movieWriter finishRecording];

自定义滤镜

此类库相比系统Core Image 的一个重要优势就是能够自定义Filter，这些Filters需要创建Shader着色器，例如：

varying highp vec2 textureCoordinate;
uniform sampler2D inputImageTexture;
void main()
{
    lowp vec4 textureColor = texture2D(inputImageTexture, textureCoordinate);
    lowp vec4 outputColor;
    outputColor.r = (textureColor.r * 0.393) + (textureColor.g * 0.769) + (textureColor.b * 0.189);
    outputColor.g = (textureColor.r * 0.349) + (textureColor.g * 0.686) + (textureColor.b * 0.168);    
    outputColor.b = (textureColor.r * 0.272) + (textureColor.g * 0.534) + (textureColor.b * 0.131);
    outputColor.a = 1.0;
    gl_FragColor = outputColor;
}

常遇到的问题

• 显示视频的View，要用GPUImageView
• 视频路径问题，例如：
  NSURL* url = [NSURL fileURLWithPath:filePath], //正确 [NSURL URLWithString:filePath] //错误
• 提示Cannot call method when status is xx
  status状态有：
  typedef NS_ENUM(NSInteger, AVAssetWriterStatus) { AVAssetWriterStatusUnknown = 0, AVAssetWriterStatusWriting, AVAssetWriterStatusCompleted, AVAssetWriterStatusFailed, AVAssetWriterStatusCancelled };

当xx为2时，代表已完成一次文件写入，解决方案：
创建新的GPUImageMovieWriter

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
    if (self.presentedViewController != nil) {
        [self resetMovieWriter];
        
    }
}
-(void)prepareWriter
{
    /*
     *moveWriter用来记录保存视频
     */
    NSString *pathToMovie = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents/Movie.m4v"];
    unlink([pathToMovie UTF8String]); // If a file already exists, AVAssetWriter won't let you record new frames, so delete the old movie
    self.movieURL = [NSURL fileURLWithPath:pathToMovie];
    self.moveWriter =[[GPUImageMovieWriter alloc] initWithMovieURL:self.movieURL size:CGSizeMake(640.0, 480.0)];
    [_filter addTarget:self.moveWriter];                    //（经过_filter传给moveWriter）
    self.moveWriter.encodingLiveVideo = YES;
    _stillCamera.audioEncodingTarget = _moveWriter;         //_moveWriter处理音频流
    [_stillCamera startCameraCapture];                      //捕获画面
}

当xx为3时，代表文件路径已存在，解决方案：

//1.删除已存在文件
unlink([pathToMovie UTF8String])  
//2.重新生成新目录         
//[_currentVideoPath stringByAppendingPathComponent:[NSString stringWithFormat:@"%lld.mp4", (long long)[[NSDate date] timeIntervalSince1970]]]