Copying depth from one RenderTexture to another

Hi there,

I know that this question has been asked already but still I could not find a definite answer and I am still struggling to make it work.

What I am doing in my program is some HDR rendering into a RenderTexture (the format ARGBHalf). Then, after applying tonemapping operator (Tonemapping.js) I continue rendering some overlays into the same RenderTexture (with another similarly setup camera with higher depth value but in LDR mode - I am not doing any tonemapping after that). The problem is that as soon as tonemapping completes the depth information is gone from the RenderTexture. I am aware that Graphics.Blit() used by Tonemapping implementation does not copy over depth info the destination RenderTexture. So to remedy that I made my HDR camera create depth texture for me (by enabling depthTexture creation)

  function Start ()
  {
      ....

      camera.depthTextureMode=DepthTextureMode.Depth;
  }

Then I am confused as to how I can use the generated texture (_CameraDepthTexture) to transfer the depth values to the destination RenderTexture. This is how I modified Tonemapping.js and this does not work:

 @ImageEffectTransformToLDR
    function OnRenderImage (source: RenderTexture, destination: RenderTexture)
    {
       CopyDepth(source, destinarion);
 
       ....
 
    }

  
 function CopyDepth (source : RenderTexture, destination : RenderTexture)
 {
     var oldRT = RenderTexture.active;
         
     Graphics.SetRenderTarget(destination.depthBuffer, destination.depthBuffer);
  
     GL.Clear(true, false, Color.clear);
  
     GL.PushMatrix();
     GL.LoadOrtho();
  
     depthCopier.SetPass(0);
  
     //Render the full screen quad manually.
     GL.Begin(GL.QUADS);
     GL.TexCoord2(0.0f, 0.0f); GL.Vertex3(0.0f, 0.0f, 0.1f);
     GL.TexCoord2(1.0f, 0.0f); GL.Vertex3(1.0f, 0.0f, 0.1f);
     GL.TexCoord2(1.0f, 1.0f); GL.Vertex3(1.0f, 1.0f, 0.1f);
     GL.TexCoord2(0.0f, 1.0f); GL.Vertex3(0.0f, 1.0f, 0.1f);
     GL.End();
  
     GL.PopMatrix();
  
     RenderTexture.active = oldRT;
 }

The shader used by the depthCopier material is this:

 Shader "Hidden/DepthCopy" 
 {
     Subshader {
     
     Tags {"RenderType"="Opaque"}
    
 // -- DepthTextureCopy
         Pass {
             Fog { Mode Off }
  
             CGPROGRAM
             #pragma vertex vert
             #pragma fragment frag
             #pragma fragmentoption ARB_precision_hint_fastest
  
             #include "UnityCG.cginc"
            
             sampler2D _CameraDepthTexture;
            
             struct appdata_t {
                 float4 vertex : POSITION;
                 float2 texcoord : TEXCOORD0;
             };
  
             struct v2f {
                 float4 vertex : POSITION;
                 float2 texcoord : TEXCOORD0;
             };
  
             v2f vert (appdata_t v)
             {
                 v2f o;
                 o.vertex = mul(UNITY_MATRIX_MVP, v.vertex);
                 o.texcoord=v.texcoord;
                 return o;
             }
  
             half4 frag (v2f i) : COLOR
             {
                 half4 depth=half4(Linear01Depth(tex2D(_CameraDepthTexture, i.uv).r));
                 return depth;
             }
             ENDCG
  
         }
  
     }
     
      Fallback off
 }