When to use multiple parts for a mesh, and when to build detail in?

Question

I am always running into the decision whether or not to make a mesh one connected mesh or to add small details as just separate parts to the model. Is there a best practices for this? Does it matter for games either way?

Answer 1

Fewer meshes equate to fewer draw calls, so generally you should try to go for as few as possible.

Split them when:

• one mesh would be so large that you'd need 32-bit index buffers to address (as this is generally too large)
• the sub-mesh uses different textures/shaders/materials
• the sub-mesh is somehow optional and might be detached or attached from the main mesh often (or similar reasons; basically you want to avoid having to update the main mesh's vertex buffer)