現在の ModelView 行列
Assigning to this variable is equivalent to glLoadMatrix(mat) in OpenGL; in other
graphics APIs the corresponding functionality is emulated.
Changing modelview matrix overrides current camera's view parameters, so most
often you want to save and restore matrix using GL.PushMatrix and GL.PopMatrix.
この変数を読み取り、現在の ModelView 行列が返されます。