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　　今天来学习一下一个简单滤镜使用的流程，通过调节亮度滤镜来了解。先将GPUImage库导入到项目中，引入头文件"GPUImage.h"

　　   一、创建亮度滤镜对象

  　   GPUImageBrightnessFilter *filter = [[GPUImageBrightnessFilter alloc] init]，经过alloc init之后，程序为我们创建了顶点数组以及帧缓冲区，纹理，并绑定为当前使用的对象。

　　1.为顶点着色添加属性

　　　首先我们来看一该滤镜的顶点着色器字符串

 

 attribute vec4 position;attribute vec4 inputTextureCoordinate;varying vec2 textureCoordinate;void main(){gl_Position = position;textureCoordinate = inputTextureCoordinate.xy;}

 

 

 我们了解到该顶点有2个需要添加的属性position，inputTextureCoordinate.我们需要在程序中添加这2个属性，通过下列方法来添加

 

- (void)initializeAttributes;
{[filterProgram addAttribute:@"position"];[filterProgram addAttribute:@"inputTextureCoordinate"];// Override this, calling back to this super method, in order to add new attributes to your vertex shader
}

 

 　2.片段着色提供uniform
　　

 varying highp vec2 textureCoordinate;uniform sampler2D inputImageTexture;uniform lowp float brightness;void main(){lowp vec4 textureColor = texture2D(inputImageTexture, textureCoordinate);gl_FragColor = vec4((textureColor.rgb + vec3(brightness)), textureColor.w);}　　

 

　　brightnessUniform = [filterProgram uniformIndex:@"brightness"]

　　filterInputTextureUniform = [filterProgram uniformIndex:@"inputImageTexture"]

　　3.启用顶点数组

　　glEnableVertexAttribArray(filterPositionAttribute);

      glEnableVertexAttribArray(filterTextureCoordinateAttribute)

 4.创建纹理

- (void)generateTexture;
{glActiveTexture(GL_TEXTURE1);glGenTextures(1, &_texture);glBindTexture(GL_TEXTURE_2D, _texture);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, _textureOptions.minFilter);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, _textureOptions.magFilter);// This is necessary for non-power-of-two textures
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, _textureOptions.wrapS);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, _textureOptions.wrapT);// TODO: Handle mipmaps
}

　
　　5.创建帧缓冲区

 　　   glGenFramebuffers(1, &framebuffer)

　　6.帧缓冲绑定纹理

　　glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, _texture, 0);

 

 　　二、设置亮度值

　　filter.brightness = value

 

　　三、设置纹理尺寸

　   [filter forceProcessingAtSize:image.size]

 

　　四、创建GPUImagePicture对象

     GPUImagePicture *pic = [[GPUImagePicture alloc] initWithImage:image]

 

　　五、向创建好的GPUImagePicture对象添加target

 

　　六，处理图像

　　[pic processImage]

 

进行图像渲染并绘制

 

    glClearColor(backgroundColorRed, backgroundColorGreen, backgroundColorBlue, backgroundColorAlpha);glClear(GL_COLOR_BUFFER_BIT);glActiveTexture(GL_TEXTURE2);glBindTexture(GL_TEXTURE_2D, [firstInputFramebuffer texture]);glUniform1i(filterInputTextureUniform, 2);    glVertexAttribPointer(filterPositionAttribute, 2, GL_FLOAT, 0, 0, vertices);glVertexAttribPointer(filterTextureCoordinateAttribute, 2, GL_FLOAT, 0, 0, textureCoordinates);glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);

 

 

 

 

　　七、[filter useNextFrameForImageCapture]

 

 　　八、获取处理后的图像

　　image ＝ [filter imageFromCurrentFramebuffer]

 

    GPUImageBrightnessFilter *filter = [[GPUImageBrightnessFilter alloc] init];filter.brightness = value;[filter forceProcessingAtSize:image.size];GPUImagePicture *pic = [[GPUImagePicture alloc] initWithImage:image];[pic addTarget:filter];[pic processImage];[filter useNextFrameForImageCapture];image ＝ [filter imageFromCurrentFramebuffer];