Its impossible to predict all the problems that will pop up in the production, but here are a few things that already have me a bit worried.
The biggest has to be fur. One of the main characters is a kitten. Unless I change the style of the film completely (which I am simply not willing to do), this kitten will need fur. For those who dont know CG/animation very well, this may seem rather silly. Can't I just click the fur button? Im not so worried about the look of the fur. To get a decent looking fur look can take months, and I expect it to, but I know that with enough tweaking, I will have the look I want. The problem comes at render time. Fur cripples render times. I dont mean it will turn a 15 minute render into a 30 minute render, I mean it will turn a 15 min render into a 5 hour render. Even with a render farm (which I plan on using somehow, even if it means selling my lung on ebay), it will be a big problem. Thats 5 hours for one frame, 30 frames = 1 second of animation. Thats a lot of hours =P
So, thats the biggest worry. Im also concerned about the animation. This is the first film ive done that does not use some form of dialogue. This means that the story will be heavily dependent of the animation. I will be hiring animators for the film, so hopefully the quality will be what I want and need. Another thing that worries me is will the rigs I am creating for my characters be good enough for an animator to work with? We shall see =)
