Thought I would start a thread regarding Carrara and the Unity Game engine as there appears to be some interest shown in another place.
If you are unaware of Unity, take a look at their website. Unity is free (there is also a paid pro version with more features).
To set the ball rolling, here are a few tips which I have found out.
Carrara – Use the right size
To get Carraras weird idea of what a metre is into unity you need to scale to 255%.
Remember in unity 1 unit = 1 Metre. Not so important for static meshes, but important for physics and characters to get scaling correct in Carrara, rather than adjusting scaling in Unity.
WHEN WORKING ON STATIC OBJECTS. Work in metres throughout. Then group all objects together and do an overall scale of 255%.
WHEN WORKING WITH BONED OBJECTS (CHARACTERS). Create mesh. Then scale up to 255% before adding bones.
The size of the your GameObject’s mesh is much more important than the mass of the Rigidbody. If you find that your Rigidbody is not behaving exactly how you expect - it moves slowly, floats, or doesn’t collide correctly - consider adjusting the scale of your mesh asset. Unity’s default unit scale is 1 unit = 1 meter, so the scale of your imported mesh is maintained, and applied to physics calculations. For example, a crumbling skyscraper is going to fall apart very differently than a tower made of toy blocks, so objects of different sizes should be modeled to accurate scale.
If you are modeling a human make sure he is around 2 meters tall in Unity. To check if your object has the right size compare it to the default cube. You can create a cube using GameObject->Create Other->Cube. The cube’s height will be exactly 1 meter, so your human should be twice as tall.
If you aren’t able to adjust the mesh itself, you can change the uniform scale of a particular mesh asset by selecting it in Project View and choosing Assets->Import Settings… from the menubar. Here, you can change the scale and re-import your mesh.
If your game requires that your GameObject needs to be instantiated at different scales, it is okay to adjust the values of your Transform’s scale axes. The downside is that the physics simulation must do more work at the time the object is instantiated, and could cause a performance drop in your game. This isn’t a terrible loss, but it is not as efficient as finalizing your scale with the other two options. Also keep in mind that non-uniform scales can create undesirable behaviors when Parenting is used. For these reasons it is always optimal to create your object at the correct scale in your modeling application.
The direction the model must be facing.
3rd Person character must face to the left in Carraras scene.
Polygons, Bones and all that jazz
Use one Skinned Mesh Renderer
Your character should use only a single skinned mesh renderer. There is usually no reason to use multiple meshes for a character. Unity also has optimizations related to visibility culling and bounding volume updating which only kick in if you use one animation component and one skinned mesh renderer in conjunction. If you care about performance, multiple skinned meshes per character is not an option. If you use two skinned mesh renderers for one character instead of one, the time spent on rendering the character will most likely double!
Don’t Use Many Materials
You also want to keep the number of materials on that mesh as low as possible. There is only one reason why you might want to have more than one material on the character: when you need to use a different shader (e.g. if you want to use a special shader for the eyes). However, 2-3 materials per character should be sufficient in almost all cases. If your character is carrying a gun, it might be useful to have the gun a separate object, simply because it might get detached.
Reduce Amount of Bones
Medium Desktop games use bone hierarchies with 15-60 bones. The fewer bones you use the faster; with 30 bones you can achieve very good quality on Desktop platforms and fairly good quality on Mobile Platforms. Unless you really have to, we strongly recommend you use fewer than 30 bones if you are developing for Mobile Platforms and around 30 bones per character on Desktop platforms.
How many polygons you should use depends on the quality you require and the platform you are targeting. Anything between 300-1500 triangles on Mobile Platforms and 500-6000 triangles on Desktop Platforms is reasonable. If you want lots of characters on screen or want the game to run on old machines, you will have to reduce the polygon count for each character. As an example: Half Life 2 characters used 2500-5000 triangles per character. Next-gen AAA games running on PS3 or Xbox 360 usually have characters with 5000-7000 triangles.