Introduction ============ This is pspi, a GIMP plug-in that interfaces to Photoshop filter plug-ins. First, the bad news: Pspi only works on systems that understand i386 Windows executables, more specifically, DLLs. (Photoshop plug-ins are actually DLLs.) Pspi was developed on (i386) Windows. It is also possible to build and use it on i386 Linux, using Wine. To build pspi, you will need the headers from the Adobe Photoshop CC 2015.5 SDK which is available at https://www.adobe.com/devnet/photoshop/sdk/eula.html To build pspi on Linux, from a terminal configure it like this: export CC=winegcc export CXX=wineg++ ./configure --with-pssdk=/path/to/pluginsdk Before compiling on Linux, you need to fix a few glitches in the SDK headers. Copy the adobe patch to /path/to/pluginsdk and do : patch -p0 < adobe_photoshop_cc_sdk.diff Debugging pspi ============== You can set the environment variable PSPI_DEBUG to have pspi print out various debugging messages at run-time, for instance (in a Windows command prompt): set PSPI_DEBUG=resource_suite:debugger (or in a Linux shell): export PSPI_DEBUG=ALL See the source code for other possible values. Obviously, this environment variable must be set before starting the GIMP (which eventually runs pspi). On Windows, as pspi is a Windows GUI application, to actually see the debugging print-out, you have to start GIMP from a command line with stdout going somewhere, for instance: gimp --verbose | cat This stdout redirection will be inherited by GIMP's children, like pspi. Run-time setup ============== Pspi has a search path consisting of folders where to search for Photoshop filter plug-ins, which are files with the extension .8BF. These folders are searched recursively. Pspi stores info about the Photoshop plug-ins found in the pspirc file in the user's personal GIMP directory. The first time a .8BF file is noticed, pspi loads it and searches for the so-called "PIPL" resources, which contain some more information about the Photoshop plug-in, for instance where it should be located in Photoshop's Filter menu. It gets a identical menu entry in GIMP's <Image>/Filter menu. Unless the .8BF file changes, it isn't loaded on subsequent GIMP starts, but only when the filter is invoked. Also files with the extensions .EFF and .DLL are checked to see if they are Photoshop plug-ins. Reverse engineering =================== The hardest thing in writing this plug-in was figuring out the stuff in the Photoshop plug-in communication that isn't clearly documented. To make the reverse engineering easier, I wrote a "proxy" Photoshop plug-in, piproxy. The Windows resources of a real Photoshop plug-in (the "target") is copied to piproxy.8bf. The target should be moved away so that Photoshop won't find it, and instead piproxy.8bf shouild be put where Photoshop will find it. Thus, piproxy gets loaded when the menu entry for the original plug-in is invoked. It then loads the original target plug-in, and starts passing calls back and forth between Photoshop and the target, while logging the stuff that passes through. This works fine. If you intend to run piproxy, set the PIPROXY_LOG and PIPROXY_TARGET environment variables. See the source code. The piproxy sources are included, but it does not get built by default. After a week of late-evening hacking, the breakthrough came when I realized that the "Handle" type in the Photoshop API is used by some plug-ins in an undocumented way. Instead of treating a Handle as an opaque type, they "know" that a Handle in fact is a pointer to a pointer, and use it like that without calling the "lock" API which is the documented way to get the pointer from a Handle. Tor Lillqvist <tml@iki.fi>, December 2001, March 2006. Ben Touchette <draekko.software+gimp@gmail.com> July 2016.