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;voidmain()
{
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 lowpfloat
brightness;voidmain()
{
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 texturesglTexParameteri(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];