Anybody to tell me why,about zdepth comparing

Unity Engine
1

I want to do a shadow mapping, i have the zdepth of light view rendered to a map and the zdepth of camera caculated.here is the initial shader code for render zdepth and the shader code for comparation:

v2f vert (appdata_base v) {
			    v2f o;
			    o.pos = mul (UNITY_MATRIX_MVP, v.vertex);
			    o.depth.xy=o.pos.zw;
			    return o;
			}
			
			float4 frag(v2f i) : COLOR {
			    float d=i.depth.x/i.depth.y;
			    float4 c=EncodeFloatRGBA(d);
			    return c;
			}

and the code to compare them

vertOut vert(appdata_base v)
		{
			vertOut o;
			o.pos=mul(UNITY_MATRIX_MVP,v.vertex);
			float4 wVertex=mul(_Object2World ,v.vertex);
			o.litPos=mul(_litMVP,wVertex);
			return o;
		}
		float4 frag(vertOut i):COLOR
		{
			float2 shadowTexc=0.5*i.litPos.xy/i.litPos.w+float2(0.5,0.5);
			float litZ=i.litPos.z/i.litPos.w;
			float4 c=tex2D(_myShadow,shadowTexc);
			float t=DecodeFloatRGBA(c);
			if(litZ>t)
			return 0.3;
			else
			return 0.7;
		}

it result something like this:

1104432--41518--$2012-12-06_133741.png
1104432--41518--$2012-12-06_133741.png800×600 17.8 KB

After i do some offset of both the z depth of light view and camera view like this

v2f vert (appdata_base v) {
			    v2f o;
			    o.pos = mul (UNITY_MATRIX_MVP, v.vertex);
			    o.depth.xy=o.pos.zw;
			    return o;
			}
			
			float4 frag(v2f i) : COLOR {
			   float d=i.depth.x/i.depth.y-4/i.depth.y;//I modified the ZDepth here
			    float4 c=EncodeFloatRGBA(d);
			    return c;
			}
			ENDCG

the shader code to compares them in camera view:

vertOut vert(appdata_base v)
		{
			vertOut o;
			o.pos=mul(UNITY_MATRIX_MVP,v.vertex);
			float4 wVertex=mul(_Object2World ,v.vertex);
			o.litPos=mul(_litMVP,wVertex);
			return o;
		}
		float4 frag(vertOut i):COLOR
		{
			float2 shc=0.5*i.litPos.xy/i.litPos.w+float2(0.5,0.5);
			float oZ=i.litPos.z/i.litPos.w-4/i.litPos.w;//I modified the ZDepth here
			float4 c=tex2D(_myShadow,shc);
			float sZ=DecodeFloatRGBA(c);
			float r=0;
			if(oZ<=sZ)
			r=0.8;
			else
			r=0.5;
			return r;
		}

the result seems correct,like this:

1108447--41751--$2012-12-11_125242.png
1108447--41751--$2012-12-11_125242.png800×600 17.9 KB

it is what i want,
but could somebody tell me why i need to offset the zdepth by this way:
float d=i.depth.x/i.depth.y-4/i.depth.y;
float oZ=i.litPos.z/i.litPos.w-4/i.litPos.w;

2

The artifact I think you’re referring to is called Peter Panning, and is the result of a workaround for shadow acne. In unity you can control the settings for this in any light source that casts shadows, and it is referred to as the bias of the shadow. You can also read more about those things here.

At least, I think that is what you were referring to, I had a little trouble reading your post.

3

:smile:You guy are so geat,sorry about my poor english,Thanks!