Custom sky box and depth mask shaders not working together

Hi there,

Hoping somebody can see what I'm missing here.

I've got a depth mask shader used to obscure certain objects. This works great, very simple. However I recently added a custom skybox shader in order to render a gradient as the background. This has lead to the depth mask material rendering black to the screen and objects drawn in front are not cleared. Code for both shaders and picture of problem below.

Thanks for reading...

Code (CSharp):

1. Shader "Skybox/GradientSkybox"
2. {
3.     Properties
4.     {
5.         _TopColor("Top Color", Color) = (1, 1, 1, 1)
6.         _BottomColor("Bottom Color", Color) = (0, 0, 0, 1)
7.         _Angle("Angle", Range(0, 360)) = 0
8.     }
9.  
10.     CGINCLUDE
11.  
12.     #include "UnityCG.cginc"
13.  
14.     struct appdata
15.     {
16.         float4 position : POSITION;
17.     };
18.  
19.     struct v2f
20.     {
21.         float4 position : SV_POSITION;
22.         float2 texcoord : TEXCOORD0;
23.     };
24.  
25.     half4 _TopColor;
26.     half4 _BottomColor;
27.     half _Angle;
28.  
29.     v2f vert(appdata v)
30.     {
31.         v2f o;
32.         o.position = UnityObjectToClipPos(v.position);
33.         o.texcoord = 0.5 * (o.position.xy / o.position.w);
34.         return o;
35.     }
36.  
37.     half4 frag(v2f i) : COLOR
38.     {
39.         float2 uv = i.texcoord;
40.  
41.         float radians = _Angle * 0.01745329;
42.         float2 rotation = float2(sin(radians), cos(radians));
43.  
44.         float topCoefficient    = dot( rotation, uv) + 0.5;
45.         float BottomCoefficient = dot(-rotation, uv) + 0.5;
46.  
47.         half4 color = topCoefficient * _TopColor + BottomCoefficient * _BottomColor;
48.  
49.         return color;
50.     }
51.  
52.     ENDCG
53.  
54.     SubShader
55.     {
56.         Tags{ "RenderType" = "Background" "Queue" = "Background" }
57.  
58.         Pass
59.         {
60.             ZWrite Off
61.             Cull Off
62.             Fog { Mode Off }
63.             CGPROGRAM
64.             #pragma fragmentoption ARB_precision_hint_fastest
65.             #pragma vertex vert
66.             #pragma fragment frag
67.             ENDCG
68.         }
69.     }
70.  
71.     CustomEditor "GradientSkyboxInspector"
72. }

Code (CSharp):

1. Shader "Unlit/DepthMask"
2. {      
3.     SubShader
4.     {
5.         Tags {"Queue" = "Geometry-10" }
6.  
7.         ColorMask 0
8.         ZWrite On
9.  
10.         Pass {}
11.     }
12. }
13.  

 

My first guess is that this is to do with draw order. For performance reasons, the skybox is drawn after opaque geometry to prevent overdraw - meaning that the skybox won't be drawn whenever something has written to the depth buffer before it. Ordinarily, this would be fine because you would have something drawn in its place, but in this case you write to the depth buffer without writing to the colour buffer. As such, the skybox rendering skips the mask's geometry, leaving nothing behind it (also explaining why objects in front appear to not be cleared). Not sure how you would get around this in the built-in render pipeline. Render queue for skyboxes doesn't do much because they are drawn separately after opaques anyway. I can only suggest not using a skybox, but instead having a regular sphere object that is always drawn in the background.

 

Hi @Namey5, I am facing this same issue and need to stick to built-in render pipeline. Is it possible to work around this by having a custom render pipeline which is created extending the built-in render pipeline and changing the skybox rendering behaviour?