Filter registration and some simple filters (also descriptions). Desperate splitting of code into small shared libraries for historical reasons presumably (OS/2 and Windows 3.x). The libraries produced from the code in each subdirectory of filter/source/graphicfilter are graphic format import or export filters. But they don't have uniform API. Some have either an GraphicImport or GraphicExport entry point, and are loaded and used in a uniform fashion from code in vcl/source/filter/graphicfilter.cxx. Others have different API and are loaded from other places. For instance "icgm" has ImportCGM, and is loaded and used by sd/source/filter/cgm/sdcgmfilter.cxx (!).