Hi there,
I'm happy to say I've added a new filter into the G'MIC plug-in, namely
Drop shadow 3d, located in subfolder
Lights & Shadows/.
This looks like this :
Attachment:
gmic_drop_shadow3d.png [ 94.96 KiB | Viewed 3177 times ]
I've tried to put the same kind of parameters as in the plug-in described in the page here :
http://www.artistic-effects.com/3d-shadow/(they are probably not the same though).
You can easily render things like this for instance, with this new G'MIC filter :
Attachment:
gmic_drop_shadow3d_2.png [ 112.42 KiB | Viewed 3177 times ]
Note that this time, the preview matches what the final result looks like

The filter code I wrote for this effect is available here, for curious people :
http://pastebin.com/diSddiE5If you succeed in using this new filter, feel free to post your results here, I'm interested by what you can get with it.