Distance shader returns strage distance when not at 0,0,0

Questions & Answers
1

i have this shader that is suposed to make objects transparent if they are to close to the camera and it works perfectly when the object is at 0,0,0 but for example when the object is at 0,0,40 i get full fade at around 0,0,20 (for this example the variables FadeStartDistance = 0 and FadeDistance = 10)

i also have a problem that the range of the fade is half, ea if i have FadeDistance = 10 then the actual lenght of the fade is 5 meters. i currectly get around this problem by multiplaying the distance by 0.5 but that doesnt seem like the right way and im guessing that the problems are related

EDIT

changed to using the correct matrix to get the worldspace and now it works for normal mashes but the problem now is that when i use it for a particle shader (im using the new 3.5 version) it again only works when its at 0,0,0 if i move it to 0,0,20 it doesnt work at all and if its at 0,0,10 i can see some particles no matter where the camera is

EDIT2

i have preformed some more testing and it seems like the Object2World matrix always is the identity matrix for particle system
is there some other matrix i can/should use instead?

Shader "Custom/DistanceFade" 
{
	Properties 
	{
	    _MainTex ("Main Tex", 2D) = "white" {}
		_FadeStartDistance ("Fade Start Distance", Float) = 0
		_FadeDistance ("Fade Distance", Float) = 0
		_MinFade ("Minimum Fade", Float) = 0
	}
	SubShader 
	{
	    Pass 
	    {
		//Blend SrcAlpha One
		//Cull Off Lighting Off ZWrite Off Fog { Color (0,0,0,0) }
		CGPROGRAM
		#pragma vertex vert
		#pragma fragment frag
		#include "UnityCG.cginc"
		
		sampler2D _MainTex;
		float4 _MainTex_ST;

		float _FadeStartDistance;
		float _FadeDistance;
		float _MinFade;
		
		struct v2f 
		{
		    float4  pos : SV_POSITION;
		    float2  uv : TEXCOORD0;
		    float	newAlpha : TEXCOORD1;
		};
		
		v2f vert (appdata_full v)
		{
		    v2f o;
		    o.pos = mul (UNITY_MATRIX_MVP, v.vertex);
		    o.uv = TRANSFORM_TEX(v.texcoord, _MainTex);
	
			float3 worldSpaceObjectPos = mul(v.vertex, _Object2World).xyz;
			float dist = distance(worldSpaceObjectPos.xyz, _WorldSpaceCameraPos.xyz);
			float fade = (dist - _FadeStartDistance) / _FadeDistance;
			fade *= fade;
			o.newAlpha = clamp(fade, _MinFade, 1.0f);
			
		    return o;
		}
		
		half4 frag (v2f i) : COLOR
		{
			fixed4 c = tex2D(_MainTex, i.uv);
			
			//c.w = i.newAlpha;
			if(i.newAlpha <= _MinFade)
				c = fixed4(1,0,0,1);
			else if(i.newAlpha >= 0.99)
				c = fixed4(0,1,0,1);
			else
				c = fixed4(i.newAlpha, i.newAlpha, i.newAlpha, 1.0f);
			
			return c;
		}
		ENDCG
		
		}
	}
}
2

I’m not an expert but are you certain to use the right matrix conversion?

If I’m not mistaking, UNITY_MATRIX_MVP transform the coordinates into screen position, whereas you are checking against world camera position. Can’t this work better with UNITY_MATRIX_MV?

Of course at the end, you will need to transform it again to screen position, with:

o.pos = mul(UNITY_MATRIX_P, o.pos);

See here for a definition of the different matrices.

3

length(mul (UNITY_MATRIX_MV,v.vertex)) is distance of vertex from camera.