Is there a way to fetch albedo/specular/smoothness/occlusion and normals in a deferred frag. shader?

The title pretty much covers it.

I want to create an opaque per-pixel fragment shader that:

• Will be rendered after all normal opaque surfaces but before all transparent surfaces
• Will have albedo, specular, smoothness, occlusion values and normals fetched from the deferred render targets (for each given pixel)
• Will output those fetched RT values

Basically, this will make the shader completely invisible, as it will just write back the content of deferred render targets. This is the base I need to create proper UE4-like normal decals and some other stuff, but those are the easy part. What I need to figure out right now is how can I get that content from RTs. I'm unable to find anything about this in the documentation, but this should be possible - after all, Unity already offers a way to fetch values like linear eye depth, so asking to fetch something like smoothness is not exactly an exotic thing.

Can anyone help me out?

 

Update: figured the fetching part out. Now, is there any info on outputting the spec/normals/emissive back from the fragment correctly? Currently I'm using this:

Code (csharp):

1.  
2.     void frag
3.     (
4.         v2f i,
5.         out half4 outDiffuse : COLOR0,            // RT0: diffuse color (rgb), --unused-- (a)
6.         out half4 outSpecRoughness : COLOR1,           // RT1: spec color (rgb), roughness (a)
7.         out half4 outNormal : COLOR2,            // RT2: normal (rgb), --unused-- (a)
8.         out half4 outEmission : COLOR3            // RT3: emission (rgb), --unused-- (a)
9.     )
10.     {
11.         float2 uv = i.screenUV.xy / i.screenUV.w;
12.         float4 gbuffer0 = tex2D (_CameraGBufferTexture0, uv);
13.         float4 gbuffer1 = tex2D (_CameraGBufferTexture1, uv);
14.         float4 gbuffer2 = tex2D (_CameraGBufferTexture2, uv);
15.  
16.         outDiffuse = gbuffer0;
17.         outSpecRoughness = gbuffer1;
18.         outNormal = gbuffer2;
19.         outEmission = gbuffer3;
20.     }
21.  

And that obviously results in just diffuse being rendered properly, because that's not a surface shader which will get shading out of the box. Nothing is lit, smoothness and normals have no influence.



How can I make the shading replicate the standard PBR setup? Do I have to cram this horrifying set of operations right into my shader to get seamless shading with Standard surfaces on background? Or is there, maybe, some helpful inline I can just plug those outputs into?

I have tried to use the same samplers in a surface shader to leverage auto shading there (with #pragma surface surf Standard and inout SurfaceOutputStandard o of course), but unfortunately I'm getting very weird artifacts with such a shader. It works only in a tiny set of object positions, as you can see here: