获取或设置原始投影矩阵，无摄像机偏移（无抖动）。
For many temporal image effects, the camera that is currently rendering needs to be slightly offset from the default projection (that is, the camera is ‘jittered’). Use this function to specify the default (non-jittered) perspective matrix that was used before the offset was applied. It is posible to configure whether the jittered or non jittered matrix should be used for objects rendered after the opaque objects pass (transparent objects for example), see [[Camera.useJitteredProjectionMatrixForTransparent].
如果同时使用了运动矢量和摄像机抖动，请使用该属性来保持帧之间的运动矢量稳定。
使用 Camera.projectionMatrix 设置抖动矩阵。