ネイティブのシャドウマップレンダーテクスチャ形式
This represents a format for which the GPU can automatically do shadowmap comparisons
for. Unity uses this format internally for shadows, when supported. Note that some
platforms or GPUs do not support Shadowmap format, in which case shadows
end up using RenderTextureFormat.Depth format.
See Also: RenderTexture class, SystemInfo.SupportsRenderTextureFormat.