GPUImageOutput类将静态图像纹理上传到OpenGL ES中，然后使用这些纹理去处理进程链中的下一个对象。它的子类可以获得滤镜处理后的图片功能。［本文讲的很少，由于有许多地方不清楚，以后会更新］

　　方法

　　- (void)setInputFramebufferForTarget:(id<GPUImageInput>)target atIndex:(NSInteger)inputTextureIndex

　　说明：用于设置指定纹理的输入帧缓冲区的尺寸

　　参数：target是具体的对象，它接受了GPUImageInput的协议，例如：当我们使用［GPUImageLookupFilter］滤镜时，target就是一个GPUImageLookupFilter的实例。

　　- (void)addTarget:(id<GPUImageInput>)newTarget atTextureLocation:(NSInteger)textureLocation

 　　说明：添加target

　　- (void)removeTarget:(id<GPUImageInput>)targetToRemove

 　　说明：删除指定的target

　　- (void)removeAllTargets

　　说明：删除所有target

　　- (UIImage *)imageFromCurrentFramebufferWithOrientation:(UIImageOrientation)imageOrientation

　　说明：从帧缓冲区中取回对象，打印在屏幕中。

　　参数：imageOrientation时当前设备的手持方向

　　- (CGImageRef)newCGImageByFilteringCGImage:(CGImageRef)imageToFilter

　　说明：使用一张静态图片做滤镜纹理

完整代码

#import "GPUImageContext.h"
#import "GPUImageFramebuffer.h"

#if TARGET_ipHONE_SIMULATOR || TARGET_OS_IPHONE
#import <UIKit/UIKit.h>
#else
// For now, just redefine this on the Mac
typedef NS_ENUM(NSInteger, UIImageOrientation) {
    UIImageOrientationUp,            // default orientation
    UIImageOrientationDown,          // 180 deg rotation
    UIImageOrientationLeft,          // 90 deg CCW
    UIImageOrientationRight,         // 90 deg CW
    UIImageOrientationUpMirrored,    // as above but image mirrored along other axis. horizontal flip
    UIImageOrientationDownMirrored,  // horizontal flip
    UIImageOrientationLeftMirrored,  // vertical flip
    UIImageOrientationRightMirrored, // vertical flip
};
#endif

void runOnMainQueueWithoutDeadlocking(void (^block)(void));
void runSynchronouslyOnVideoPRocessingQueue(void (^block)(void));
void runAsynchronouslyOnVideoProcessingQueue(void (^block)(void));
void runSynchronouslyOnContextQueue(GPUImageContext *context, void (^block)(void));
void runAsynchronouslyOnContextQueue(GPUImageContext *context, void (^block)(void));
void reportAvailableMemoryForGPUImage(NSString *tag);

@class GPUImageMovieWriter;

/** GPUImage's base source object
 
 Images or frames of video are uploaded from source objects, which are subclasses of GPUImageOutput. These include:
 
 - GPUImageVideoCamera (for live video from an iOS camera) 
 - GPUImageStillCamera (for taking photos with the camera)
 - GPUImagePicture (for still images)
 - GPUImageMovie (for movies)
 
 Source objects upload still image frames to OpenGL ES as textures, then hand those textures off to the next objects in the processing chain.
 */
@interface GPUImageOutput : NSObject
{
    GPUImageFramebuffer *outputFramebuffer;
    
    NSMutableArray *targets, *targetTextureIndices;
    
    CGSize inputTextureSize, cachedMaximumOutputSize, forcedMaximumSize;
    
    BOOL overrideInputSize;
    
    BOOL allTargetsWantMonoChromeData;
    BOOL usingNextFrameForImageCapture;
}

@property(readwrite, nonatomic) BOOL shouldSmoothlyScaleOutput;
@property(readwrite, nonatomic) BOOL shouldIgnoreUpdatesToThisTarget;
@property(readwrite, nonatomic, retain) GPUImageMovieWriter *audioEncodingTarget;
@property(readwrite, nonatomic, unsafe_unretained) id<GPUImageInput> targetToIgnoreForUpdates;
@property(nonatomic, copy) void(^frameProcessingCompletionBlock)(GPUImageOutput*, CMTime);
@property(nonatomic) BOOL enabled;
@property(readwrite, nonatomic) GPUTextureOptions outputTextureOptions;

/// @name Managing targets
- (void)setInputFramebufferForTarget:(id<GPUImageInput>)target atIndex:(NSInteger)inputTextureIndex;
- (GPUImageFramebuffer *)framebufferForOutput;
- (void)removeOutputFramebuffer;
- (void)notifyTargetsAboutNewOutputTexture;

/** Returns an array of the current targets.
 */
- (NSArray*)targets;

/** Adds a target to receive notifications when new frames are available.
 
 The target will be asked for its next available texture.
 
 See [GPUImageInput newFrameReadyAtTime:]
 
 @param newTarget Target to be added
 */
- (void)addTarget:(id<GPUImageInput>)newTarget;

/** Adds a target to receive notifications when new frames are available.
 
 See [GPUImageInput newFrameReadyAtTime:]
 
 @param newTarget Target to be added
 */
- (void)addTarget:(id<GPUImageInput>)newTarget atTextureLocation:(NSInteger)textureLocation;

/** Removes a target. The target will no longer receive notifications when new frames are available.
 
 @param targetToRemove Target to be removed
 */
- (void)removeTarget:(id<GPUImageInput>)targetToRemove;

/** Removes all targets.
 */
- (void)removeAllTargets;

/// @name Manage the output texture

- (void)forceProcessingAtSize:(CGSize)frameSize;
- (void)forceProcessingAtSizeRespectingaspectRatio:(CGSize)frameSize;

/// @name Still image processing

- (void)useNextFrameForImageCapture;
- (CGImageRef)newCGImageFromCurrentlyProcessedOutput;
- (CGImageRef)newCGImageByFilteringCGImage:(CGImageRef)imageToFilter;

// Platform-specific image output methods
// If you're trying to use these methods, remember that you need to set -useNextFrameForImageCapture before running -processImage or running video and calling any of these methods, or you will get a nil image
#if TARGET_IPHONE_SIMULATOR || TARGET_OS_IPHONE
- (UIImage *)imageFromCurrentFramebuffer;
- (UIImage *)imageFromCurrentFramebufferWithOrientation:(UIImageOrientation)imageOrientation;
- (UIImage *)imageByFilteringImage:(UIImage *)imageToFilter;
- (CGImageRef)newCGImageByFilteringImage:(UIImage *)imageToFilter;
#else
- (NSImage *)imageFromCurrentFramebuffer;
- (NSImage *)imageFromCurrentFramebufferWithOrientation:(UIImageOrientation)imageOrientation;
- (NSImage *)imageByFilteringImage:(NSImage *)imageToFilter;
- (CGImageRef)newCGImageByFilteringImage:(NSImage *)imageToFilter;
#endif

- (BOOL)providesMonochromeOutput;

@end

#import "GPUImageOutput.h"
#import "GPUImageMovieWriter.h"
#import "GPUImagePicture.h"
#import <mach/mach.h>

void runOnMainQueueWithoutDeadlocking(void (^block)(void))
{
    if ([NSThread isMainThread])
    {
        block();
    }
    else
    {
        dispatch_sync(dispatch_get_main_queue(), block);
    }
}

void runSynchronouslyOnVideoProcessingQueue(void (^block)(void))
{
    dispatch_queue_t videoProcessingQueue = [GPUImageContext sharedContextQueue];
#if !OS_OBJECT_USE_OBJC
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wdeprecated-declarations"
    if (dispatch_get_current_queue() == videoProcessingQueue)
#pragma clang diagnostic pop
#else
    if (dispatch_get_specific([GPUImageContext contextKey]))
#endif
    {
        block();
    }else
    {
        dispatch_sync(videoProcessingQueue, block);
    }
}

void runAsynchronouslyOnVideoProcessingQueue(void (^block)(void))
{
    dispatch_queue_t videoProcessingQueue = [GPUImageContext sharedContextQueue];
    
#if !OS_OBJECT_USE_OBJC
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wdeprecated-declarations"
    if (dispatch_get_current_queue() == videoProcessingQueue)
#pragma clang diagnostic pop
#else
    if (dispatch_get_specific([GPUImageContext contextKey]))
#endif
    {
        block();
    }else
    {
        dispatch_async(videoProcessingQueue, block);
    }
}

void runSynchronouslyOnContextQueue(GPUImageContext *context, void (^block)(void))
{
    dispatch_queue_t videoProcessingQueue = [context contextQueue];
#if !OS_OBJECT_USE_OBJC
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wdeprecated-declarations"
    if (dispatch_get_current_queue() == videoProcessingQueue)
#pragma clang diagnostic pop
#else
        if (dispatch_get_specific([GPUImageContext contextKey]))
#endif
        {
            block();
        }else
        {
            dispatch_sync(videoProcessingQueue, block);
        }
}

void runAsynchronouslyOnContextQueue(GPUImageContext *context, void (^block)(void))
{
    dispatch_queue_t videoProcessingQueue = [context contextQueue];
    
#if !OS_OBJECT_USE_OBJC
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wdeprecated-declarations"
    if (dispatch_get_current_queue() == videoProcessingQueue)
#pragma clang diagnostic pop
#else
        if (dispatch_get_specific([GPUImageContext contextKey]))
#endif
        {
            block();
        }else
        {
            dispatch_async(videoProcessingQueue, block);
        }
}

void reportAvailableMemoryForGPUImage(NSString *tag) 
{    
    if (!tag)
        tag = @"Default";
    
    struct task_basic_info info;
    
    mach_msg_type_number_t size = sizeof(info);
    
    kern_return_t kerr = task_info(mach_task_self(),
                                   
                                   TASK_BASIC_INFO,
                                   
                                   (task_info_t)&info,
                                   
                                   &size);    
    if( kerr == KERN_SUCCESS ) {        
        NSLog(@"%@ - Memory used: %u", tag, (unsigned int)info.resident_size); //in bytes
    } else {        
        NSLog(@"%@ - Error: %s", tag, mach_error_string(kerr));        
    }    
}

@implementation GPUImageOutput

@synthesize shouldSmoothlyScaleOutput = _shouldSmoothlyScaleOutput;
@synthesize shouldIgnoreUpdatesToThisTarget = _shouldIgnoreUpdatesToThisTarget;
@synthesize audioEncodingTarget = _audioEncodingTarget;
@synthesize targetToIgnoreForUpdates = _targetToIgnoreForUpdates;
@synthesize frameProcessingCompletionBlock = _frameProcessingCompletionBlock;
@synthesize enabled = _enabled;
@synthesize outputTextureOptions = _outputTextureOptions;

#pragma mark -
#pragma mark Initialization and teardown

- (id)init; 
{
    if (!(self = [super init]))
    {
        return nil;
    }

    targets = [[NSMutableArray alloc] init];
    targetTextureIndices = [[NSMutableArray alloc] init];
    _enabled = YES;
    allTargetsWantMonochromeData = YES;
    usingNextFrameForImageCapture = NO;
    
    // set default texture options
    _outputTextureOptions.minFilter = GL_LINEAR;
    _outputTextureOptions.magFilter = GL_LINEAR;
    _outputTextureOptions.wrapS = GL_CLAMP_TO_EDGE;
    _outputTextureOptions.wrapT = GL_CLAMP_TO_EDGE;
    _outputTextureOptions.internalFormat = GL_RGBA;
    _outputTextureOptions.format = GL_BGRA;
    _outputTextureOptions.type = GL_UNSIGNED_BYTE;

    return self;
}

- (void)dealloc 
{
    [self removeAllTargets];
}

#pragma mark -
#pragma mark Managing targets

- (void)setInputFramebufferForTarget:(id<GPUImageInput>)target atIndex:(NSInteger)inputTextureIndex;
{
    [target setInputFramebuffer:[self framebufferForOutput] atIndex:inputTextureIndex];
}

- (GPUImageFramebuffer *)framebufferForOutput;
{
    return outputFramebuffer;
}

- (void)removeOutputFramebuffer;
{
    outputFramebuffer = nil;
}

- (void)notifyTargetsAboutNewOutputTexture;
{
    for (id<GPUImageInput> currentTarget in targets)
    {
        NSInteger indexOfObject = [targets indexOfObject:currentTarget];
        NSInteger textureIndex = [[targetTextureIndices objectAtIndex:indexOfObject] integerValue];
        
        [self setInputFramebufferForTarget:currentTarget atIndex:textureIndex];
    }
}

- (NSArray*)targets;
{
    return [NSArray arrayWithArray:targets];
}

- (void)addTarget:(id<GPUImageInput>)newTarget;
{
    NSInteger nextAvailableTextureIndex = [newTarget nextAvailableTextureIndex];
    [self addTarget:newTarget atTextureLocation:nextAvailableTextureIndex];
    
    if ([newTarget shouldIgnoreUpdatesToThisTarget])
    {
        _targetToIgnoreForUpdates = newTarget;
    }
}

- (void)addTarget:(id<GPUImageInput>)newTarget atTextureLocation:(NSInteger)textureLocation;
{
    if([targets containsObject:newTarget])
    {
        return;
    }
    
    cachedMaximumOutputSize = CGSizeZero;
    runSynchronouslyOnVideoProcessingQueue(^{
        [self setInputFramebufferForTarget:newTarget atIndex:textureLocation];
        [targets addObject:newTarget];
        [targetTextureIndices addObject:[NSNumber numberWithInteger:textureLocation]];
        
        allTargetsWantMonochromeData = allTargetsWantMonochromeData && [newTarget wantsMonochromeInput];
    });
}

- (void)removeTarget:(id<GPUImageInput>)targetToRemove;
{
    if(![targets containsObject:targetToRemove])
    {
        return;
    }
    
    if (_targetToIgnoreForUpdates == targetToRemove)
    {
        _targetToIgnoreForUpdates = nil;
    }
    
    cachedMaximumOutputSize = CGSizeZero;
    
    NSInteger indexOfObject = [targets indexOfObject:targetToRemove];
    NSInteger textureIndexOfTarget = [[targetTextureIndices objectAtIndex:indexOfObject] integerValue];

    runSynchronouslyOnVideoProcessingQueue(^{
        [targetToRemove setInputSize:CGSizeZero atIndex:textureIndexOfTarget];
        [targetToRemove setInputRotation:kGPUImageNoRotation atIndex:textureIndexOfTarget];

        [targetTextureIndices removeObjectAtIndex:indexOfObject];
        [targets removeObject:targetToRemove];
        [targetToRemove endProcessing];
    });
}

- (void)removeAllTargets;
{
    cachedMaximumOutputSize = CGSizeZero;
    runSynchronouslyOnVideoProcessingQueue(^{
        for (id<GPUImageInput> targetToRemove in targets)
        {
            NSInteger indexOfObject = [targets indexOfObject:targetToRemove];
            NSInteger textureIndexOfTarget = [[targetTextureIndices objectAtIndex:indexOfObject] integerValue];
            
            [targetToRemove setInputSize:CGSizeZero atIndex:textureIndexOfTarget];
            [targetToRemove setInputRotation:kGPUImageNoRotation atIndex:textureIndexOfTarget];
        }
        [targets removeAllObjects];
        [targetTextureIndices removeAllObjects];
        
        allTargetsWantMonochromeData = YES;
    });
}

#pragma mark -
#pragma mark Manage the output texture

- (void)forceProcessingAtSize:(CGSize)frameSize;
{
    
}

- (void)forceProcessingAtSizeRespectingAspectRatio:(CGSize)frameSize;
{
}

#pragma mark -
#pragma mark Still image processing

- (void)useNextFrameForImageCapture;
{

}

- (CGImageRef)newCGImageFromCurrentlyProcessedOutput;
{
    return nil;
}

- (CGImageRef)newCGImageByFilteringCGImage:(CGImageRef)imageToFilter;
{
    GPUImagePicture *stillImageSource = [[GPUImagePicture alloc] initWithCGImage:imageToFilter];
    
    [self useNextFrameForImageCapture];
    [stillImageSource addTarget:(id<GPUImageInput>)self];
    [stillImageSource processImage];
    
    CGImageRef processedImage = [self newCGImageFromCurrentlyProcessedOutput];
    
    [stillImageSource removeTarget:(id<GPUImageInput>)self];
    return processedImage;
}

- (BOOL)providesMonochromeOutput;
{
    return NO;
}

#pragma mark -
#pragma mark Platform-specific image output methods

#if TARGET_IPHONE_SIMULATOR || TARGET_OS_IPHONE

- (UIImage *)imageFromCurrentFramebuffer;
{
    UIDeviceOrientation deviceOrientation = [[UIDevice currentDevice] orientation];
    UIImageOrientation imageOrientation = UIImageOrientationLeft;
    switch (deviceOrientation)
    {
        case UIDeviceOrientationPortrait:
            imageOrientation = UIImageOrientationUp;
            break;
        case UIDeviceOrientationPortraitUpsideDown:
            imageOrientation = UIImageOrientationDown;
            break;
        case UIDeviceOrientationLandscapeLeft:
            imageOrientation = UIImageOrientationLeft;
            break;
        case UIDeviceOrientationLandscapeRight:
            imageOrientation = UIImageOrientationRight;
            break;
        default:
            imageOrientation = UIImageOrientationUp;
            break;
    }
    
    return [self imageFromCurrentFramebufferWithOrientation:imageOrientation];
}

- (UIImage *)imageFromCurrentFramebufferWithOrientation:(UIImageOrientation)imageOrientation;
{
    CGImageRef cgImageFromBytes = [self newCGImageFromCurrentlyProcessedOutput];
    UIImage *finalImage = [UIImage imageWithCGImage:cgImageFromBytes scale:1.0 orientation:imageOrientation];
    CGImageRelease(cgImageFromBytes);
    
    return finalImage;
}

- (UIImage *)imageByFilteringImage:(UIImage *)imageToFilter;
{
    CGImageRef image = [self newCGImageByFilteringCGImage:[imageToFilter CGImage]];
    UIImage *processedImage = [UIImage imageWithCGImage:image scale:[imageToFilter scale] orientation:[imageToFilter imageOrientation]];
    CGImageRelease(image);
    return processedImage;
}

- (CGImageRef)newCGImageByFilteringImage:(UIImage *)imageToFilter
{
    return [self newCGImageByFilteringCGImage:[imageToFilter CGImage]];
}

#else

- (NSImage *)imageFromCurrentFramebuffer;
{
    return [self imageFromCurrentFramebufferWithOrientation:UIImageOrientationLeft];
}

- (NSImage *)imageFromCurrentFramebufferWithOrientation:(UIImageOrientation)imageOrientation;
{
    CGImageRef cgImageFromBytes = [self newCGImageFromCurrentlyProcessedOutput];
    NSImage *finalImage = [[NSImage alloc] initWithCGImage:cgImageFromBytes size:NSZeroSize];
    CGImageRelease(cgImageFromBytes);
    
    return finalImage;
}

- (NSImage *)imageByFilteringImage:(NSImage *)imageToFilter;
{
    CGImageRef image = [self newCGImageByFilteringCGImage:[imageToFilter CGImageForProposedRect:NULL context:[NSGraphicsContext currentContext] hints:nil]];
    NSImage *processedImage = [[NSImage alloc] initWithCGImage:image size:NSZeroSize];
    CGImageRelease(image);
    return processedImage;
}

- (CGImageRef)newCGImageByFilteringImage:(NSImage *)imageToFilter
{
    return [self newCGImageByFilteringCGImage:[imageToFilter CGImageForProposedRect:NULL context:[NSGraphicsContext currentContext] hints:nil]];
}

#endif

#pragma mark -
#pragma mark accessors

- (void)setAudioEncodingTarget:(GPUImageMovieWriter *)newValue;
{    
    _audioEncodingTarget = newValue;
    if( ! _audioEncodingTarget.hasAudioTrack )
    {
        _audioEncodingTarget.hasAudioTrack = YES;
    }
}

-(void)setOutputTextureOptions:(GPUTextureOptions)outputTextureOptions
{
    _outputTextureOptions = outputTextureOptions;
    
    if( outputFramebuffer.texture )
    {
        glBindTexture(GL_TEXTURE_2D,  outputFramebuffer.texture);
        //_outputTextureOptions.format
        //_outputTextureOptions.internalFormat
        //_outputTextureOptions.magFilter
        //_outputTextureOptions.minFilter
        //_outputTextureOptions.type
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, _outputTextureOptions.wrapS);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, _outputTextureOptions.wrapT);
        glBindTexture(GL_TEXTURE_2D, 0);
    }
}

@end