スクリプトからメッシュの頂点とインデックスにアクセスできるかどうか
Making a mesh readable will keep two copies of it in memory, one for rendering and one
in system memory for script access. Setting isReadable to false therefore saves memory.
Scaling a mesh with different amounts along the three axes (i.e. non-uniform scaling)
requires the mesh to be readable for correct lighting.
Play モードでなければ、Unity エディターではアクセスを常に許可されます。