Meshes make up a large part of your 3D worlds. Aside from some Asset store plugins, Unity does not include modelling tools. Unity does however have great interactivity with most 3D modelling packages. Unity supports triangulated or Quadrangulated polygon meshes. Nurbs, Nurms, Subdiv surfaces must be converted to polygons.
Unity supports importing Meshes from two different types of files:
Unity can import and use both types of files, and each come with their own advantages and disadvantages.
Unity can import proprietary files from the following DCC software: Max, Maya, Blender, Cinema4D, Modo, Lightwave & Cheetah3D. Files imported this way are converted into .fbx files by Unity during the import process.
Note: Assets saved as .ma, .mb, .max, .c4d, or .blend files fail to import unless you have the corresponding DCC software installed in your computer. This means that everybody working on your Unity project must have the correct software installed. For example, if you use Maya to create ExampleModel.mb and copy it into your project, anyone else opening that project also needs to have Maya installed on their computer.
Here are some guidelines for directly supported 3D applications, others can most often export file type listed above.
Unity will attempt to find the textures used by a mesh automatically on import by following a specific search plan. First, the importer will look for a sub-folder called Textures within the same folder as the mesh or in any parent folder. If this fails, an exhaustive search of all textures in the project will be carried out. Although slightly slower, the main disadvantage of the exhaustive search is that there could be two or more textures in the project with the same name. In this case, it is not guaranteed that the right one will be found.
For each imported material Unity will apply the following rules:-
If material generation is disabled (i.e. Import Materials is unchecked), then it will assign the Default-Diffuse material. If it is enabled then it will do the following:
Unity uses two main types of colliders: Mesh Colliders and Primitive Colliders. Mesh colliders are components that use imported mesh data and can be used for environment collision. When you enable Generate Colliders in the Import Settings, a Mesh collider is automatically added when the mesh is added to the Scene. It will be considered solid as far as the physics system is concerned.
If you are moving the object around (a car for example), you can not use Mesh colliders. Instead, you will have to use Primitive colliders. In this case you should disable the Generate Colliders setting.
Animations are automatically imported from the scene. For more details about animation import options see the section on asset preparation and import in the Mecanim animation system.
If you have a character with a normal map that was generated from a high-polygon version of the model, you should import the game-quality version with a Smoothing angle of 180 degrees. This will prevent odd-looking seams in lighting due to tangent splitting. If the seams are still present with these settings, enable Split tangents across UV seams.
If you are converting a greyscale image into a normal map, you don’t need to worry about this.
Unity has support for BlendShapes (also called morph-targets or vertex level animation). Unity can import BlendShapes from .FBX (BlendShapes and controlling aninimation) and .dae (only BlendShapes) exported 3D files. Unity BlendShapes support vertex level animation on vertices, normals and tangents. Mesh can be affected by skin and BlendShapes at the same time. All meshes imported with BlendShapes will use SkinnedMeshRenderer (no mater if it does have skin or not). BlendShape animation is imported as part of regular animation - it simply animates BlendShape weights on SkinnedMeshRenderer.
There are two ways to import BlendShapes with normals:
If you want tangents on your BlendShapes then set Tangents import mode to Calculate.
This is correct. What you are looking at is the number of vertices/triangles actually being sent to the GPU for rendering. In addition to the case where the material requires them to be sent twice, other things like hard-normals and non-contiguous UVs increase vertex/triangle counts significantly compared to what a modeling app tells you. Triangles need to be contiguous in both 3D and UV space to form a strip, so when you have UV seams, degenerate triangles have to be made to form strips - this bumps up the count.