QuickLook plugins and Core Image filters

Question

I'm writing a QuickLook plugin that uses a custom (system-wide installed) Core Image filter to combine two left/right views into an anaglyph. When launched through "qlmanage -p", everything works fine. But from the finder, the preview is blank... I attached to quicklookd and set some breakpoints to see what happens; there are no errors but the filter's output is a gray image. Mac OS X 10.6 with XCode 3.2.5. The plugin is marked as needing execution in the main thread.

Any hints ?

Answer 1

qlmanage process is a little different than the real process (quicklookd) that will execute your plugin. In short, qlmanage -p can connect to the window server while quicklookd forbids it, thus the different behaviors.

If you really want qlmanage to test your plugin in the same condition of quicklookd, try "qlmanage -p -z" instead of just "qlmanage -p". Only it won't display the result. You can then use gdb to debug your plugin.