modifying Z-buffer depth

Unity Engine
1

does anyone know if there is a way to modify what is being written to the z-buffer in a shader ?
for example adding noise or using a texture or alpha channel to modify the z-depth ?

thx in advance

2

Yes, this is called offset. Here is an explanation in the Unity Documentation:

But I am not sure if this works with textures since it is a parameter.

1 Like
3

Thanks, I didn’t know about offset, that may be useful.
But I guess I should have posted more info… I was thinking is it possible to do on a per pixel bases, in fragment shader ?

4

there is an entire tutorial somewhere about z clashing and offset tricks here:

https://www.google.fr/search?q=zclashing+unity&oq=zclashing+unity&aqs=chrome…69i57j69i60l2j69i61j69i59l2.2787j0&sourceid=chrome&espv=2&es_sm=93&ie=UTF-8#es_sm=93&espv=2&psj=1&q=z++fighting+unity&tbm=vid

5

It should be possible in latest version of Unity, but I haven’t tried it yet.

Try googling unity/cg depth output or something like that.
IRC it need at least Shader Model 4, so DX11 in Unity, but I may be wrong.

6

In the vertex shader, does modifying the Z coord write to depth, or does depth get written before that?

7

hrmmm shader model 4 ? I guess not possible for mobile then :confused: ?
still … worth researching though. Thanks for the replies.

8

It works on iOS. did you see
Unity iOS ShaderLab - Tutorial 10-1 (Z-Fighting) - YouTube
Unity iOS ShaderLab - Tutorial 10-2 (Offset) - YouTube

9

Depth is written per pixel (as a pixel could still be discarded in fragment shader e.g. alpha cutoff)

It is also possible in DX9 to write depth directly, however mobile seems to be a no-go according to Aras:
http://forum.unity3d.com/threads/66153-Writing-depth-value-in-fragment-program

Shader "Custom/WriteDepth" {
	Properties {
		_MainTex ("Base (RGB)", 2D) = "white" {}
	}
	SubShader {
		Tags { "RenderType"="Opaque" }

		Pass {
            CGPROGRAM        
                #pragma exclude_renderers gles flash
                #pragma vertex vert
                #pragma fragment frag
                
                #include "UnityCG.cginc"
                				
                struct v2f {
                    float4 pos : POSITION;
                    float2 uv : TEXCOORD0;
                };
                
                struct fout {
                    half4 color : COLOR;
                    float depth : DEPTH;
                };                
               
                uniform sampler2D _MainTex;
                
                v2f vert (appdata_base v) {
                    v2f vo;
                    vo.pos = mul( UNITY_MATRIX_MVP, v.vertex );
                    vo.uv = v.texcoord.xy;
                    return vo;
                }
             
                fout frag( v2f i ) {               
                    fout fo;
                    fo.color = tex2D(_MainTex, i.uv);
					fo.depth = 0.99;
                    return fo;
                }
            ENDCG
            }
	
	} 
	FallBack "Diffuse"
}
10

thanks Big Bug.
shame its not possible on mobile… yet

11

OK but how would I modify the Depth? The following example forces to hide the texture. Also I get very strange behaviour like adding float2(0) vs. float2(0,0), which should be the same, right?

struct v2f {
    float4 pos : POSITION;
    float2 uv : TEXCOORD0;
    float2 depth : TEXCOORD1;
};
                   
v2f vert (appdata_base v) {
    v2f o;
    o.pos = mul( UNITY_MATRIX_MVP, v.vertex );
    o.uv = v.texcoord.xy;
	UNITY_TRANSFER_DEPTH(o.depth);
    return o;
}
                 
half4 frag( v2f i ) : COLOR {
	fixed4 c = tex2D(_MainTex, i.uv);
	float2 depth = i.depth;
	UNITY_OUTPUT_DEPTH(depth);

	return float4(c.rgb * _Color.rgb, c.a);
}