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I was looking up 3D character models from various games (Battlefield 3 and DMC to be specific), just as research work and upon importing the model into Blender3D, I found that every part of the model was a separate mesh/object (head, armor vest, legs, hands, etc.).

This got me thinking: Why didn't the artist model them as a single object?

I think that would be better because:

  1. You can save a few polygons in your model [*].

  2. Doesn't animating separate parts [**] cause clipping issues as one mesh may not deform in sync with neighboring mesh?

[*] All parts were overlapping each other = the armor vest was overlapping chest polygons, which were not visible and thus wasted.

[**] All polygons and edges connected to each other.

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One central reason would be that in order to assign different materials, you need different entities / meshes / sub-objects. You don't need to have an individual object for each minor element (such as the mouth or the lips of a head) if you are applying a texture later, but UV unwrapping a few not so complex object separately and applying then a material is easier than UV unwrapping a single high-complex mesh.

Also: The polygon count is not a really relevant statistic anymore in contemporary 3D. Batchable draw operations are usually much more crucial to prevent unnecessary drawcalls / state switches. See the following extract from the Unity Graphics Performance page:

Typical bottlenecks and ways to check for them:

  1. GPU is often limited by fillrate or memory bandwidth. Does running the game at lower display resolution make it faster? If so, you’re most likely limited by fillrate on the GPU.

  2. CPU is often limited by the number of things that need to be rendered, also known as “draw calls”. Check “draw calls” in Rendering Statistics window; if it’s more than several thousand (for PCs) or several hundred (for mobile), then you might want to optimize the object count.

Regarding animation: It depends on what kind of animation one is using: If you are working with a deformation approach (think "Armature" in Blender terms or "morph-target animation" or "vertex blending animation" in general) than a single object should work. But for bone based approaches individual objects make handling it usually easier.

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