Pre-rendered backgrounds with zDepth baked

I'm using a fixed camera in unity and realised I could cheat a bit by pre-rendering all my static objects (Background), using a collision mesh for interaction and a zDepth image from max (Some parts need to be infront of others etc).

I found some old discussions from people wanting to recreate this effect (mainly from old games like Final Fantasy and Resident Evil).

But I figured some of you people might have a better understanding on how to practically do this?

1 - I would like to hear your ideas regarding the ZBuffer. How could I alter it in a simple and easy way?
2 - Is there a way to do shadows on top of this? More specifically I want to have shadows generated from my interactive objects ontop of the prerendered background.

Thanks in advance! I'm new to unity but so far I really dig it!

 

Ok, so I got it working, kinda. I'm using this shader:

Code (CSharp):

1. Shader "Custom/DioramaBG" {
2.     Properties {
3.         _RGB ("Base (RGB)", 2D) = "white" {}
4.         _DEPTH ("Base (RGB)", 2D) = "white" {}
5.     }
6.     SubShader {
7.         Pass {
8.             CGPROGRAM
9.             #pragma target 4.0
10.             #pragma vertex vert
11.             #pragma fragment frag
12.             #include "UnityCG.cginc"
13.              
14.             sampler2D _RGB;
15.             sampler2D _DEPTH;
16.          
17.             struct v2f
18.             {
19.                 float4 position : POSITION;
20.                 float2 uv : TEXCOORD0;
21.             };
22.          
23.             struct fragOut
24.             {
25.                 half4 color : COLOR;
26.                 float depth : DEPTH;
27.             };
28.                  
29.             v2f vert(appdata_base v)
30.             {
31.                 v2f o;
32.                 o.position = mul(UNITY_MATRIX_MVP, v.vertex);
33.                 o.uv = v.texcoord;
34.                 return o;
35.             }
36.  
37.             fragOut frag(in v2f i)
38.             {
39.                 fragOut o;
40.                 o.color = tex2D(_RGB, i.uv);
41.                 o.depth = tex2D(_DEPTH, i.uv);
42.                 return o;
43.             }
44.             ENDCG
45.         }
46.     }
47. }
48.  

I'm placing a quad in front of the camera with this shader on top with a depth texture and colors assigned to it.
It works fine except for some rounding errors on the depth.., I'm guessing the zbuffer texture needs to have a higher bit but it could also just be that it reads from my texture badly.

I'll explore more and see what is the problem (I get jaggies around objects in my prerendered scene when placing "real" objects halfway into them.., maybe I'll post a pic later).

 

So a small update.., The jaggies are gone, turned off mip-mapping and changed filter mode to point and I render to a format that matches either 2048 or 4096 right now. looks really smooth!

One thing though.., I can get SSAO (screen space ambient occlusion) to work with my realtime objects.., but nothing happens with my pre-rendered background.., anybody have any ideas about that?.., I'll probably attach some image later to gain interest in this thread. (can't just upload the original since client secrecy.., yeah)

 

sounds very cool, hope you release this script.

 

You'll have to look into what buffers are needed for SSAO. I think you'll need screen space normals and depth.

 

Just wanted to update with the finished result