Resolved Why pixels in the second pass are not drawen in a transparent shader?

This is a simple outline shader, draw the object first, then draw a bigger one as the outline.

Code (CSharp):

1. Shader "Unlit/OutLine"
2. {
3.    Properties
4.    {
5.        _Color("Color",Color) = (0,0,0,1)
6.        _Color2("Color 2",Color) = (0,0,0,0)
7.    }
8.  
9.    SubShader
10.    {
11.        Tags
12.        {
13.            "RenderType" = "Transparent"
14.            "Queue" = "Transparent"
15.        }
16.        Blend SrcAlpha OneMinusSrcAlpha
17.  
18.        Pass
19.        {
20.            Name "Front"
21.            Cull Back
22.  
23.            CGPROGRAM
24.            #include "UnityCG.cginc"
25.            #pragma vertex vert
26.            #pragma fragment frag
27.  
28.            uniform float4 _Color;
29.  
30.            float4 vert(float3 v : POSITION) : SV_POSITION
31.            {
32.                return UnityObjectToClipPos(v);
33.            }
34.  
35.            float4 frag() : COLOR { return _Color; }
36.            ENDCG
37.        }
38.  
39.        Pass
40.        {
41.            Name "Back"
42.            Cull Front
43.  
44.            CGPROGRAM
45.            #include "UnityCG.cginc"
46.            #pragma vertex vert
47.            #pragma fragment frag
48.  
49.            uniform float4 _Color2;
50.            struct vin { float3 vertex : POSITION; float3 normal : NORMAL; };
51.  
52.            float4 vert(vin v) : SV_POSITION
53.            {
54.                v.vertex.xyz += v.normal * 0.1;
55.                return UnityObjectToClipPos(v.vertex);
56.            }
57.  
58.            float4 frag() : COLOR { return _Color2; }
59.            ENDCG
60.        }
61.    }
62. }

Because this is a transparent shader, so I think z-write is disabled by default and pixels in the second should be drawen and blended with the first pass, but they are not.

• Left: normal rendering result
• Right: reversed pass order

Here is the material settings, the object is green, the outline is red.

 

ZWrite is not disabled unless you manually disable it for vertex fragment shaders.

 

You solved my confusion, thanks a lot.