Blur Material Single Pass Instanced for AR - unity3d

Question

so I am trying to make a material which causes all rendered objects behind it to be blurred. It is important for me to not be a global or screen space effect. I need a kind of mask, which is why I chose this approach.
I found some blur shader which works perfectly and just as I need it, but only in non XR rendering. As soon as I enabled the Single Pass Instanced rendering (or testing on the AR device) this does not work anymore.
Since I am not that good in shader-stuff, I quickly found out that there are some special things to be considered when doing single pass instanced shaders, or multi view shaders in general. What I did so far is changing the return-type of frags to SV_Target, change sample2d to UNITY_DECLARE_SCREENSPACE_TEXTURE and added all these UNITY_X macros to the functions, as described in the doc.
But for some reason, the effect does not work at all. Depending on my changes, I see nothing, and sometimes I see some weird artifacts going on.
Is there something else I forgot to make this shader work as I described? My biggest fear is that the vert-part of the shader does not work for multiview rendering, since the calculations might be off and require a more complicated approach?! But I am not good when it comes to such kind of math. (For now I removed the distort part of the shader, since this did not work at all.)
Shader "Custom/MRTKBlur"
{
Properties{
_Color("Main Color", Color) = (1,1,1,1)
_BumpAmt("Distortion", Range(0,128)) = 10
_MainTex("Tint Color (RGB)", 2D) = "white" {}
_BumpMap("Normalmap", 2D) = "bump" {}
_Size("Size", Range(0, 20)) = 1
}
Category{
// We must be transparent, so other objects are drawn before this one.
Tags { "Queue" = "Transparent+1" "IgnoreProjector" = "True" "RenderType" = "TransparentCutout" }
LOD 200
SubShader {
// Horizontal blur
GrabPass {
Tags { "LightMode" = "Always" }
}
Pass {
Blend SrcAlpha OneMinusSrcAlpha
ZWrite On
Lighting Off
Tags { "LightMode" = "Always" }
CGPROGRAM
#pragma vertex vert
#pragma fragment frag
#pragma fragmentoption ARB_precision_hint_fastest
#include "UnityCG.cginc"
struct appdata_t {
float4 vertex : POSITION;
float2 texcoord: TEXCOORD0;
UNITY_VERTEX_INPUT_INSTANCE_ID
};
struct v2f {
float4 vertex : SV_POSITION;
float4 uvgrab : TEXCOORD0;
UNITY_VERTEX_INPUT_INSTANCE_ID
UNITY_VERTEX_OUTPUT_STEREO
};
v2f vert(appdata_t v) {
v2f o;
UNITY_SETUP_INSTANCE_ID(v); //Insert
UNITY_TRANSFER_INSTANCE_ID(v, o);
UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(o); //Insert
o.vertex = UnityObjectToClipPos(v.vertex);
#if UNITY_UV_STARTS_AT_TOP
float scale = -1.0;
#else
float scale = 1.0;
#endif
o.uvgrab.xy = (float2(o.vertex.x, o.vertex.y * scale) + o.vertex.w) * 0.5;
o.uvgrab.zw = o.vertex.zw;
return o;
}
UNITY_DECLARE_SCREENSPACE_TEXTURE(_GrabTexture);
float4 _GrabTexture_TexelSize;
float _Size;
half4 frag(v2f i) : SV_TARGET {
UNITY_SETUP_INSTANCE_ID(i);
half4 sum = half4(0,0,0,0);
#if UNITY_SINGLE_PASS
#define GRABPIXEL(weight,kernelx) UNITY_SAMPLE_SCREENSPACE_TEXTURE( _GrabTexture, UNITY_PROJ_COORD(UnityStereoScreenSpaceUVAdjust(float4(i.uvgrab.x + _GrabTexture_TexelSize.x * kernelx*_Size, i.uvgrab.y, i.uvgrab.z, i.uvgrab.w), _GrabTexture_TexelSize))) * weight
#else
#define GRABPIXEL(weight,kernelx) UNITY_SAMPLE_SCREENSPACE_TEXTURE( _GrabTexture, ((float4(i.uvgrab.x + _GrabTexture_TexelSize.x * kernelx*_Size, i.uvgrab.y, i.uvgrab.z, i.uvgrab.w), _GrabTexture_TexelSize))) * weight
#endif
sum += GRABPIXEL(0.05, -4.0);
sum += GRABPIXEL(0.09, -3.0);
sum += GRABPIXEL(0.12, -2.0);
sum += GRABPIXEL(0.15, -1.0);
sum += GRABPIXEL(0.18, 0.0);
sum += GRABPIXEL(0.15, +1.0);
sum += GRABPIXEL(0.12, +2.0);
sum += GRABPIXEL(0.09, +3.0);
sum += GRABPIXEL(0.05, +4.0);
return sum;
}
ENDCG
}
// Vertical blur
GrabPass {
Tags { "LightMode" = "Always" }
}
Pass {
Tags { "LightMode" = "Always" }
Blend SrcAlpha OneMinusSrcAlpha
ZWrite On
Lighting Off
CGPROGRAM
#pragma vertex vert
#pragma fragment frag
#pragma fragmentoption ARB_precision_hint_fastest
#include "UnityCG.cginc"
struct appdata_t {
float4 vertex : POSITION;
float2 texcoord: TEXCOORD0;
UNITY_VERTEX_INPUT_INSTANCE_ID
};
struct v2f {
float4 vertex : SV_POSITION;
float4 uvgrab : TEXCOORD0;
UNITY_VERTEX_INPUT_INSTANCE_ID
UNITY_VERTEX_OUTPUT_STEREO
};
v2f vert(appdata_t v) {
v2f o;
UNITY_SETUP_INSTANCE_ID(v); //Insert
UNITY_TRANSFER_INSTANCE_ID(v, o);
UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(o); //Insert
o.vertex = UnityObjectToClipPos(v.vertex);
#if UNITY_UV_STARTS_AT_TOP
float scale = -1.0;
#else
float scale = 1.0;
#endif
o.uvgrab.xy = (float2(o.vertex.x, o.vertex.y * scale) + o.vertex.w) * 0.5;
o.uvgrab.zw = o.vertex.zw;
return o;
}
UNITY_DECLARE_SCREENSPACE_TEXTURE(_GrabTexture);
float4 _GrabTexture_TexelSize;
float _Size;
half4 frag(v2f i) : SV_Target {
UNITY_SETUP_INSTANCE_ID(i);
half4 sum = half4(0,0,0,0);
#if UNITY_SINGLE_PASS
#define GRABPIXEL(weight,kernelx) UNITY_SAMPLE_SCREENSPACE_TEXTURE( _GrabTexture, UNITY_PROJ_COORD(UnityStereoScreenSpaceUVAdjust(float4(i.uvgrab.x + _GrabTexture_TexelSize.x * kernelx*_Size, i.uvgrab.y, i.uvgrab.z, i.uvgrab.w), _GrabTexture_TexelSize))) * weight
#else
#define GRABPIXEL(weight,kernelx) UNITY_SAMPLE_SCREENSPACE_TEXTURE( _GrabTexture, ((float4(i.uvgrab.x + _GrabTexture_TexelSize.x * kernelx*_Size, i.uvgrab.y, i.uvgrab.z, i.uvgrab.w), _GrabTexture_TexelSize))) * weight
#endif
//G(X) = (1/(sqrt(2*PI*deviation*deviation))) * exp(-(x*x / (2*deviation*deviation)))
sum += GRABPIXEL(0.05, -4.0);
sum += GRABPIXEL(0.09, -3.0);
sum += GRABPIXEL(0.12, -2.0);
sum += GRABPIXEL(0.15, -1.0);
sum += GRABPIXEL(0.18, 0.0);
sum += GRABPIXEL(0.15, +1.0);
sum += GRABPIXEL(0.12, +2.0);
sum += GRABPIXEL(0.09, +3.0);
sum += GRABPIXEL(0.05, +4.0);
return sum;
}
ENDCG
}
/*
// Distortion
GrabPass {
Tags { "LightMode" = "Always" }
}
Pass {
Tags { "LightMode" = "Always" }
CGPROGRAM
#pragma vertex vert
#pragma fragment frag
#pragma fragmentoption ARB_precision_hint_fastest
#include "UnityCG.cginc"
struct appdata_t {
float4 vertex : POSITION;
float2 texcoord: TEXCOORD0;
UNITY_VERTEX_INPUT_INSTANCE_ID
};
struct v2f {
float4 vertex : SV_POSITION;
float4 uvgrab : TEXCOORD0;
float2 uvbump : TEXCOORD1;
float2 uvmain : TEXCOORD2;
UNITY_VERTEX_INPUT_INSTANCE_ID
UNITY_VERTEX_OUTPUT_STEREO
};
float _BumpAmt;
float4 _BumpMap_ST;
float4 _MainTex_ST;
v2f vert(appdata_t v) {
v2f o;
UNITY_SETUP_INSTANCE_ID(v);
UNITY_TRANSFER_INSTANCE_ID(v, o);
UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(o);
o.vertex = UnityObjectToClipPos(v.vertex);
#if UNITY_UV_STARTS_AT_TOP
float scale = -1.0;
#else
float scale = 1.0;
#endif
o.uvgrab.xy = (float2(o.vertex.x, o.vertex.y * scale) + o.vertex.w) * 0.5;
o.uvgrab.zw = o.vertex.zw;
o.uvbump = TRANSFORM_TEX(v.texcoord, _BumpMap);
o.uvmain = TRANSFORM_TEX(v.texcoord, _MainTex);
return o;
}
fixed4 _Color;
UNITY_DECLARE_SCREENSPACE_TEXTURE(_GrabTexture);
float4 _GrabTexture_TexelSize;
sampler2D _BumpMap;
sampler2D _MainTex;
half4 frag(v2f i) : SV_Target {
UNITY_SETUP_INSTANCE_ID(i);
// calculate perturbed coordinates
half2 bump = UnpackNormal(tex2D(_BumpMap, i.uvbump)).rg; // we could optimize this by just reading the x y without reconstructing the Z
float2 offset = bump * _BumpAmt * _GrabTexture_TexelSize.xy;
i.uvgrab.xy = offset * i.uvgrab.z + i.uvgrab.xy;
half4 col = UNITY_SAMPLE_SCREENSPACE_TEXTURE(_GrabTexture, i.uvgrab.xy / i.uvgrab.w);
half4 tint = tex2D(_MainTex, i.uvmain) * _Color;
return col * tint;
}
ENDCG
}
*/
}
}
}