Can someone explain what a filter chain is in GPUImage in simple words?

Question

I realize GPUImage has been well documented and there's a lot of instructions on how to use it on the main github page. However, it fails to explain what a filter chain is - what's addTarget? What's missing is a simple enough diagram showing what needs to be added to what. Is it always GPUImageView (source?) -> add target -> [filter]? I'm sorry if this sounds daft, but I fail to follow the correct sequence given there are so many ways of using it. To me, it sounds like you're connecting it the other way round (such as saying: Connect the socket to the TV). Why not add filter to the source? I'm trying to use it but I get lost in all the addTargets. Thanks!

Answer 1

You can think of it as a series of inputs and outputs. Look in the GPUImage framework project to see which are inputs (typically filters) and which are outputs (imageview, moviewriter, etc..). Every target effects the next target in the chain.

Example:

GPUImageMovie -> GPUImageSepiaFilter -> GPUImageMovieWriter

A movie will be sent to the sepia filter that will perform its job, the movie with a sepia filter applied will be sent to the movie writer, then the movie writer will export a movie with a sepia filter applied.

To help visualize what's going on, any node editor program typically uses this scheme. Think of calling addTarget: as one of the connections in the attached image.

A google image search for Node Editor will give you plenty of other image to help picture what adding targets does.