Android RenderTexture format depth, sampler failed on android/ios gles.

I wanna to use a RenderTexture ,format Depth, on Android/IOS . As I already use lightmap soft in scene., so I cann't use Camera.depthTextureMode = DepthTextureMode.Depth , for that gonna cause a depth texture conflict. So I have to user RenderTexture, format Depth instead .
So I rendered a debug depth texture, that works well on PC , but faied on mobile device. I know that gles use ARB_Format for depth texture, did I sample it wrong?
I just use "tex2D(_DepthTexture, i.uv).r" .
my shader :

Code (CSharp):

1. Shader "Image Effects/Fog of War"
2. {
3.     Properties
4.     {
5.         _MainTex ("Base (RGB)", 2D) = "white" {}
6.     }
7.     SubShader
8.     {
9.         Pass
10.         {
11.             ZTest Always
12.             Cull Off
13.             ZWrite Off
14.             Fog { Mode off }
15.                  
16. CGPROGRAM
17. #pragma vertex vert
18. #pragma fragment frag
19. #pragma fragmentoption ARB_precision_hint_fastest
20. #include "UnityCG.cginc"
21. sampler2D _MainTex;
22. sampler2D _DepthTexture;
23.  
24. uniform float4x4 _InverseMVP;
25. uniform float _Ratio;
26.  
27. struct Input
28. {
29.     float4 position : POSITION;
30.     float2 uv : TEXCOORD0;
31. };
32.  
33. Input vert (appdata_full v)
34. {
35.     Input o;
36.     o.position = mul(UNITY_MATRIX_MVP, v.vertex);
37.     o.uv = v.texcoord.xy;
38.     return o;
39. }
40.  
41. float3 CamToWorld (in float2 uv, in float depth)
42. {
43.     float4 pos = float4(uv.x, uv.y, depth, 1.0);
44.     pos.xyz = pos.xyz * 2.0 - 1.0;
45.     pos = mul(_InverseMVP, pos);
46.     return pos.xyz / pos.w;
47. }
48.  
49. fixed4 frag (Input i) : COLOR
50. {
51.     half4 original = tex2D(_MainTex, i.uv);  
52. //    return original;
53. //#if SHADER_API_D3D9||SHADER_API_D3D10||SHADER_API_D3D11
54. //    float2 depthUV = i.uv;
55. //    //depthUV.y = lerp(depthUV.y, 1.0 - depthUV.y, _CamPos.w);
56. //    //depthUV.y = 1.0 - depthUV.y;
57. //    float depth = tex2D(_DepthTexture, depthUV).r;
58. //    float3 pos = CamToWorld(depthUV, depth);
59. //    float4 debug = float4(pos.z*0.05,pos.z*0.05,pos.z*0.05,1);
60. //    return debug;
61. //#else
62.     float depth = tex2D(_DepthTexture, i.uv).r;
63.     float3 pos = CamToWorld(i.uv, depth);
64.     float4 debug = float4(pos.z*_Ratio,pos.z*_Ratio,pos.z*_Ratio,1);
65.     return debug;
66. //#endif
67. }
68.  
69. ENDCG
70.         }
71.     }
72.     Fallback off
73. }

 

I build a debug sample proj ,to render the depth sample of a cub , on the screen. You can see , that works fine in Editor, but fails on mobile devices.

depth test screen image:

proj link:
https://mega.nz/#!TI82yCyA!MeWG5-6H73pdNNUBO6THcpSTwQZ7lt8CFlf2RnFD4lQ