Unity 3D - Shaders with alpha break depth of field - unity3d

Question

I have a scene where I really need depth of field.
Apparently, Unity's depth of field doesn't work with any of the shaders, neither built-in or custom, that process the alpha.
So this happens, for example, with the Transparent/Diffuse shader. Transparent/Cutout works instead.
Here's the simplest custom shader I made that triggers this behaviour:
Shader "Custom/SimpleAlpha" {
Properties {
_MainTex ("Base (RGBA)", 2D) = "white" {}
}
SubShader {
Tags { "RenderType"="Transparent" "Queue"="Transparent" }
//Tags { "RenderType"="Opaque" }
LOD 300
ZWrite Off
CGPROGRAM
#pragma surface surf Lambert alpha
#include "UnityCG.cginc"
sampler2D _MainTex;
struct Input {
float2 uv_MainTex;
};
void surf (Input IN, inout SurfaceOutput o) {
half4 c = tex2D (_MainTex, IN.uv_MainTex);
o.Albedo = c.rgb;
o.Alpha = c.a;
}
ENDCG
}
FallBack "Diffuse"
}
If you try the code in a project you'll notice that EVERY object that wears the shader is blurred with the very same amount instead of being blurred basing on Z.
Any help is much appreciated.
Thanks in advance.
I posted the same question on Unity Answers: http://answers.unity3d.com/questions/438556/my-shader-brakes-depth-of-field.html

Answer 1

Since depth of field is a post processing effect that uses the values stored in the Z-buffer, the following line is the culprit:
ZWrite Off
For transparent objects, Z-buffer writes are usually disabled because the Transparent render queue doesn't need the Z-buffer.
So if you remove that line, you should see depth of field correctly applied to transparent objects. But objects lying behind fully transparent areas will now be blurred using the wrong Z value. As quick fix, you could try to use an alpha test like AlphaTest Greater 0.1.