How To Get The Depth Texture of Objects That Drawed By "Graphics.DrawProceduralNow"?

Hi,
I use this shader to get depth texture ,It worked when camera rendering common models,but failed when I use
Graphics.DrawProceduralNow() in "OnRenderObject()",

Code (CSharp):

1. half4 frag (v2f i) : COLOR{
2.    float depthValue =Linear01Depth (tex2Dproj(_CameraDepthTexture,UNITY_PROJ_COORD(i.scrPos)).r);
3.    half4 depth;
4.    depth.r = depthValue;
5.    depth.g = depthValue;
6.    depth.b = depthValue;
7.    depth.a = 1;
8.    return depth;
9. }