GPUImage的filter的textures处理链式结构

 1 @protocol GPUImageInput <NSObject>
 2 - (void)newFrameReadyAtTime:(CMTime)frameTime atIndex:(NSInteger)textureIndex;
 3 - (void)setInputFramebuffer:(GPUImageFramebuffer *)newInputFramebuffer atIndex:(NSInteger)textureIndex;
 4 - (NSInteger)nextAvailableTextureIndex;
 5 - (void)setInputSize:(CGSize)newSize atIndex:(NSInteger)textureIndex;
 6 - (void)setInputRotation:(GPUImageRotationMode)newInputRotation atIndex:(NSInteger)textureIndex;
 7 - (CGSize)maximumOutputSize;
 8 - (void)endProcessing;
 9 - (BOOL)shouldIgnoreUpdatesToThisTarget;
10 - (BOOL)enabled;
11 - (BOOL)wantsMonochromeInput;
12 - (void)setCurrentlyReceivingMonochromeInput:(BOOL)newValue;
13 @end

 1 　　  CGDataProviderRef dataProvider = NULL;
 2         if ([GPUImageContext supportsFastTextureUpload])
 3         {
 4 #if TARGET_IPHONE_SIMULATOR || TARGET_OS_IPHONE
 5             NSUInteger paddedWidthOfImage = CVPixelBufferGetBytesPerRow(renderTarget) / 4.0; 　　//字节对齐后的图片占用宽度可能要大
 6             NSUInteger paddedBytesForImage = paddedWidthOfImage * (int)_size.height * 4;
 7             
 8             glFinish();　　　　//强制提交前面调用的gl指令到GPU硬件，阻塞调用
 9             CFRetain(renderTarget); //防止出现野指针，在回调中释放 I need to retain the pixel buffer here and release in the data source callback to prevent its bytes from being prematurely deallocated during a photo write operation
10             [self lockForReading];
11             rawImagePixels = (GLubyte *)CVPixelBufferGetBaseAddress(renderTarget); 
12             dataProvider = CGDataProviderCreateWithData((__bridge_retained void*)self, rawImagePixels, paddedBytesForImage, dataProviderUnlockCallback);
　　　　　　//全局的framebuffercache强引用当前自身，防止framebuffer在切换时出现问题
13             [[GPUImageContext sharedFramebufferCache] addFramebufferToActiveImageCaptureList:self]; // In case the framebuffer is swapped out on the filter, need to have a strong reference to it somewhere for it to hang on while the image is in existence
14 #else
15 #endif
16         }
17         else
18         {
19             [self activateFramebuffer];
20             rawImagePixels = (GLubyte *)malloc(totalBytesForImage);
21             glReadPixels(0, 0, (int)_size.width, (int)_size.height, GL_RGBA, GL_UNSIGNED_BYTE, rawImagePixels);  //阻塞调用，直接从framebuffer中读取image 原始数据
22             dataProvider = CGDataProviderCreateWithData(NULL, rawImagePixels, totalBytesForImage, dataProviderReleaseCallback);
23             [self unlock]; // Don‘t need to keep this around anymore
24         }

/** 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.
 */

/** GPUImage‘s base filter class
 
 Filters and other subsequent elements in the chain conform to the GPUImageInput protocol, 
 which lets them take in the supplied or processed texture from the previous link in the chain and do something with it. 
 Objects one step further down the chain are considered targets, 
 and processing can be branched by adding multiple targets to a single output or filter.
 */

- (void)setInputFramebuffer:(GPUImageFramebuffer *)newInputFramebuffer atIndex:(NSInteger)textureIndex;

{

    firstInputFramebuffer = newInputFramebuffer;

    [firstInputFramebuffer lock];

}

- (void)newFrameReadyAtTime:(CMTime)frameTime atIndex:(NSInteger)textureIndex;
{
    static const GLfloat imageVertices[] = {
        -1.0f, -1.0f,
        1.0f, -1.0f,
        -1.0f,  1.0f,
        1.0f,  1.0f,
    };　　　　//顶点数据，两个三角形组成texture区域
　　　　
    [self renderToTextureWithVertices:imageVertices textureCoordinates:[[self class] textureCoordinatesForRotation:inputRotation]];

    [self informTargetsAboutNewFrameAtTime:frameTime];
}

- (void)renderToTextureWithVertices:(const GLfloat *)vertices textureCoordinates:(const GLfloat *)textureCoordinates;
{
    if (self.preventRendering)
    {
        [firstInputFramebuffer unlock];
        return;
    }
    
    [GPUImageContext setActiveShaderProgram:filterProgram];

　　/**
　　　* 从GPUImageFrameBufferCache中取出可重用的outputFramebuffer
　　　*
　　　**/
    outputFramebuffer = [[GPUImageContext sharedFramebufferCache] fetchFramebufferForSize:[self sizeOfFBO] textureOptions:self.outputTextureOptions onlyTexture:NO];

    [outputFramebuffer activateFramebuffer];
    if (usingNextFrameForImageCapture)
    {
        [outputFramebuffer lock];
    }

    [self setUniformsForProgramAtIndex:0];
    
    glClearColor(backgroundColorRed, backgroundColorGreen, backgroundColorBlue, backgroundColorAlpha);
    glClear(GL_COLOR_BUFFER_BIT);
    
    glActiveTexture(GL_TEXTURE2);   //选择GL_TEXTURE2
    glBindTexture(GL_TEXTURE_2D, [firstInputFramebuffer texture]); //绑定当前输入的framebuffer中的texture
    
    glUniform1i(filterInputTextureUniform, 2);    
　　//分别设置顶点shader中的顶点数据，和将来用于片元shader中的texture坐标数据
    glVertexAttribPointer(filterPositionAttribute, 2, GL_FLOAT, 0, 0, vertices);
    glVertexAttribPointer(filterTextureCoordinateAttribute, 2, GL_FLOAT, 0, 0, textureCoordinates);
    
    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
    
    [firstInputFramebuffer unlock];
    
    if (usingNextFrameForImageCapture)
    {
        dispatch_semaphore_signal(imageCaptureSemaphore);
    }
}

- (void)presentFramebuffer;
{
    glBindRenderbuffer(GL_RENDERBUFFER, displayRenderbuffer);
    [[GPUImageContext sharedImageProcessingContext] presentBufferForDisplay];
}