GPUImage中亮度调整的实现——GPUImageBrightnessFilter

亮度brightness其实是对RGB的调整，RGB值越大，效果越亮；反之则越暗。

GPUImage中提供了对图像亮度调整的Filter，其核心代码如下(fragment)：

 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);
 }

 其中brightness的取值范围为[-1,1]