Shake and Combustion are not really "competitors" in the every sense of the word....
The main difference between the two software packages is that Shake is a node-based system where as Combustion is a layer-based system. In fact, Combustion has been often described as a blend between a layer enviroment (much like After Effects) and a node environment like Shake (or Digital Fusion.)
Shake is an awesome application, no question about that. The major strengths that I respect in Shake are 2D workgroup film compositing, generating a processing pipeline based on scripts, managing group assets, and a render engine that is very intelligent in terms of how it uses processing power. So, simply put Shake is great for film work. ( Note that Combustion does film wotk too...)
But there are other types of compositing work besides film -- For example, some jobs will have the need to create quick motion graphics using vector-based painting tools, or maybe want to use an After Effects plug-ins for a certain shot, or maybe create a SWF Flash file for a website, or perhaps work in 3D / X-Y-Z space......... You see, all THOSE functions are things that Combustion does and Shake can't. As for Plug-Ins, Shake has a growing list of third-party choices, but it still doesn't match the fact that Combustion accepts many, many AE compatible plug-ins. Further, with the Combustion v3 update, you also get a kool Warping/Morphing plug-in from Re:Flex thrown in..
Lastly is simply PRICE.. If it is YOUR money you are spending, first off the purchase price is very different: about $5000 for Shake MAC (double that if you want Linux!) vs. $1000 for Combustion (either Mac or PC.) That's a big difference !
But on the other hand, I know of many professional effects and production houses in that use BOTH Shake and Combustion, for the many reasons I've just mentioned...
Bye,
jack
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