private void CreateCamera()
{
if (_camera == null)
{
var camGo = new GameObject("ShadowMap Camera");
_camera = camGo.AddComponent <Camera>();
_cameraTrans = _camera.transform;
// 如果改成专用的阴影的话，DC的耗时应该能降低，相对应的RT格式也得更改
_camera.SetReplacementShader(ShaderHelper.Find(ShaderHelper.DepthPass), ShaderHelper.RenderTypeTag);
}
_camera.backgroundColor = Color.white;
_camera.clearFlags = CameraClearFlags.SolidColor;
_camera.orthographic = true;
_camera.targetTexture = _shadowMap;
// 没必要额外生成阴影贴图
// _camera.depthTextureMode = DepthTextureMode.Depth;
_camera.depthTextureMode = DepthTextureMode.None;
_camera.orthographicSize = _cameraSize;
_camera.nearClipPlane = _cameraNear;
_camera.farClipPlane = _cameraFar;
_camera.allowHDR = false;
// 采用渲染物体的Layer，可能得更改
_camera.cullingMask = 1 << gameObject.layer;
UpdateCameraPosition();
CheckUpdateCameraMatrix(true);
}