Surfaces are created to be rendered using a primitive, which may be any of the values defined in PrimitiveType.

The arrays argument is an array of arrays. Each of the Mesh.ARRAY_MAX elements contains an array with some of the mesh data for this surface as described by the corresponding member of ArrayType or null if it is not used by the surface. For example, arrays[0] is the array of vertices. That first vertex sub-array is always required; the others are optional. Adding an index array puts this surface into "index mode" where the vertex and other arrays become the sources of data and the index array defines the vertex order. All sub-arrays must have the same length as the vertex array (or be an exact multiple of the vertex array's length, when multiple elements of a sub-array correspond to a single vertex) or be empty, except for Mesh.ARRAY_INDEX if it is used.

The blend_shapes argument is an array of vertex data for each blend shape. Each element is an array of the same structure as arrays, but Mesh.ARRAY_VERTEX, Mesh.ARRAY_NORMAL, and Mesh.ARRAY_TANGENT are set if and only if they are set in arrays and all other entries are null.

The lods argument is a dictionary with float keys and PackedInt32Array values. Each entry in the dictionary represents an LOD level of the surface, where the value is the Mesh.ARRAY_INDEX array to use for the LOD level and the key is roughly proportional to the distance at which the LOD stats being used. I.e., increasing the key of an LOD also increases the distance that the objects has to be from the camera before the LOD is used.

The flags argument is the bitwise OR of, as required: One value of ArrayCustomFormat left shifted by ARRAY_FORMAT_CUSTOMn_SHIFT for each custom channel in use, Mesh.ARRAY_FLAG_USE_DYNAMIC_UPDATE, Mesh.ARRAY_FLAG_USE_8_BONE_WEIGHTS, or Mesh.ARRAY_FLAG_USES_EMPTY_VERTEX_ARRAY.

Note: When using indices, it is recommended to only use points, lines, or triangles.

normal_merge_angle is in degrees and used in the same way as the importer settings in lods.

normal_split_angle is not used and only remains for compatibility with older versions of the API.

The number of generated lods can be accessed using get_surface_lod_count(), and each LOD is available in get_surface_lod_size() and get_surface_lod_indices().

bone_transform_array is an Array which can be either empty or contain Transform3Ds which, for each of the mesh's bone IDs, will apply mesh skinning when generating the LOD mesh variations. This is usually used to account for discrepancies in scale between the mesh itself and its skinning data.

This method caches the returned mesh, and subsequent calls will return the cached data until clear() is called.

If not yet cached and base_mesh is provided, base_mesh will be used and mutated.