{GPUImageFilterGroup`的用途是什么？

Question

GPUImageFilterGroup的用途是什么？

为什么我们需要完成所有addFilter，setInitialFilters，setTerminalFilter步骤？我们甚至需要addTarget来使用组中的过滤器？ filters中的initialFilters和GPUImageFilterGroup.m有什么区别？

GPUImageFilterGroup是否可能仅收到一个filters数组，并设置setInitialFilters，setTerminalFilter，甚至为要添加的过滤器一一添加目标？

        case GPUIMAGE_FILTERGROUP:
        {
            self.title = @"Filter Group";
            self.filterSettingsSlider.hidden = NO;

            [self.filterSettingsSlider setValue:0.05];
            [self.filterSettingsSlider setMinimumValue:0.0];
            [self.filterSettingsSlider setMaximumValue:0.3];

            filter = [[GPUImageFilterGroup alloc] init];

            GPUImageSepiaFilter *sepiaFilter = [[GPUImageSepiaFilter alloc] init];
            [(GPUImageFilterGroup *)filter addFilter:sepiaFilter];

            GPUImagePixellateFilter *pixellateFilter = [[GPUImagePixellateFilter alloc] init];
            [(GPUImageFilterGroup *)filter addFilter:pixellateFilter];

            [sepiaFilter addTarget:pixellateFilter];
            [(GPUImageFilterGroup *)filter setInitialFilters:[NSArray arrayWithObject:sepiaFilter]];
            [(GPUImageFilterGroup *)filter setTerminalFilter:pixellateFilter];
        }; break;