I've had "make a screensaver that uses my kimdaba archive directly" on my todo list for rather a long time. Thanks to hiveminder, it finally percolated to the top... and turned out to be easier than I thought. (Not done, but easier.)
First step: find out how xscreensaver modules are written in the first
place. Found a simple, though somewhat out of date, tutorial on
writing them in C. Turns out that all that really matters is "draw
something on someone else's window". (The tutorial has it as the root
window; the modern implementation uses $XSCREENSAVER_WINDOW
passed in the environment in hex.)
As sort of a tribute to the tutorial (for getting me off the ground), I duplicated the first exercise from scratch in python. xss_simplesquares.py does the same thing as the first tutorial, with two modifications:
Most of the use of python-xlib is painfully straightforward.
The one trick is generating a window object from 0x80059E. After
turning it into a number with int(windowid, 16), all you have to
do is display.create_resource_object('window', windowid) to
create a wrapper object that works just like any window you'd create
directly.
You can just add this code to your .xscreensaver file, using the
gui, or just add it to the programs: entry with all of the
others.
Next step: actually tie this in with the other kimdaba/kphotoalbum
XML file parsing code around here, and add an image renderer; that
should be enough to implement "any picture with the tag(s) given on
the commandline gets displayed". The hard part will be finding the
motivation; these days, my photos-in-progress working set is on a
memory stick, and not actually plugged in to the laptop.
(Also, don't let the lack of recent changes to python-xlib deter
you; the protocol hasn't changed in many years, after all - even the
code from my late-90's TPJ article on "Xlib in Pure Perl" still
works. I am of course much more interested in the python version
these days :-)
Footnotes: