Just started to get my hands dirty on the node compositing on Blender. First question is how to get the view constantly updated? Not necessarily realtime, but at least when I move the time forward I want to see what’s happening there. Also when I change the material on an object in a scene I don’t get updated aswell. Anything I should do?
err… bumpity bump 
http://blenderartists.org/forum/showthread.php?t=76480
See if anything in the link I posted in that thread helps.
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nope, nothing helps on that one. I have to render at least 1 frame then it’ll appear on the preview node and image viewer. When I change the scene the both preview (on the node and image viewer window) don’t update at all. Each time I use compositing node, the input node are always empty. I’ve checked the composit node effects thread, no post pointing to this problem aswell. 
Anyone have experience with the node compositing plz help?