Question ShaderLab ZClip False produces unexpected result on Android with OpenGLES3

Dear Forum,

I have run into an issue with ZClip False. The shader behaves as expected in the Editor and on iOS. However behavior is different for Android OpenGLES3.

GOAL: Write a shader that also renders triangles behind the clip plane

Using below shader, triangles will be drawn when they are behind the near clip plane and part of the renderer is at least in front of the near clip plane.

This can be achieved using ZClip False.

Code (Boo):

1. Shader "NoZClip"
2. {
3.     Properties
4.     {
5.         _Color("Color", Color) = (1,1,1,1)
6.     }
7.         SubShader
8.     {
9.         Tags { "RenderType" = "Opaque" "Queue" = "Geometry"}
10.         Pass
11.         {
12.             Name "DrawWithoutZTest"
13.             Cull Off
14.             ZClip False
15.  
16.             CGPROGRAM
17.             #pragma vertex vert
18.             #pragma fragment frag
19.             #include "UnityCG.cginc"
20.  
21.             half4 _Color;
22.  
23.             half4 vert(float4 v : POSITION) : SV_POSITION
24.             {
25.                 return UnityObjectToClipPos(v);
26.             }
27.              
28.             half4 frag() : SV_Target
29.             {
30.                 return _Color;
31.             }
32.             ENDCG
33.         }
34.     }
35. }
36.  

EXPECTED BEHAVIOR: Renderer should NOT be clipped
- Unity 2022.3.4f1

The shader works as expected in Unity Editor on Windows.

The test scene includes 2 duplicate quads: one is fully inside the viewing frustum whereas the other cuts the near clip plane.





UNEXPECTED BEHAVIOR: Renderer gets clipped on Android phone
- Samsung Galaxy S20 FE
- OpenGLES3

The renderer gets clipped. The result is different from the editor, and also from iOS builds.



QUESTIONS:
- Is the shown behavior expected behavior on Android OpenGLES3?
- If so are there any options to replicate Editor behavior on Android?

Thank you so much for your feedback and ideas!

 

Thank you very much for your prompt and informative reply @aleksandrk

So if I understand correctly Shaderlab's ZClip=False will translate into "GL_EXT_depth_clamp" when using OpenGLES3.x and feature "depthClamp" for Vulkan API respectively? Or in other words availability of the respective feature on the target hardware would guarantee the shader to work?

 

OK thanks a lot! You definitely helped me with the issue!