Using Depth Textures
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Using Depth Textures

It is possible to create Render Textures where each pixel contains a high precision "depth" value (see RenderTextureFormat.Depth). This is mostly used when some effects need scene's depth to be available (for example, soft particles, screen space ambient occlusion, translucency would all need scene's depth).

Depth textures in Unity are implemented differently on different platforms.

Using depth texture helper macros

Most of the time depth textures are used to render depth from the camera. UnityCG.cginc helper include file contains some macros to deal with the above complexity in this case:

For example, this shader would render depth of its objects:

Shader "Render Depth" {
SubShader {
    Tags { "RenderType"="Opaque" }
    Pass {
        Fog { Mode Off }
CGPROGRAM
#pragma vertex vert
#pragma fragment frag
#include "UnityCG.cginc"

struct v2f {
    float4 pos : POSITION;
    float depth : TEXCOORD0;
};

v2f vert( appdata_base v ) {
    v2f o;
    o.pos = mul(glstate.matrix.mvp, v.vertex);
    TRANSFER_EYEDEPTH(o.depth);
    return o;
}

half4 frag(v2f i) : COLOR {
    OUTPUT_EYEDEPTH(i.depth);
}
ENDCG
    }
} 
}