Problems with writing a cutout shader, that can recieve shadows

eI tried multiple approaches, but non of them worked.

Here a try with two shader passes:

```
Shader "Cutout" {

Properties {
_MainTex ("Base (RGB)", 2D) = "white" {}
_Tint ("Tint", Color) = (1, 1, 1, 1)
_Brightness ("Brightness", Range(0,4)) = 1.25
_Light ("Light", Color) = (0, 0, 0, 1)
_Shadows ("Shadows", Range(0,1)) = 0.75
_Contrast ("Contrast", Range(-1,1)) = 0.0
_Cutoff ("Alpha cutoff", Range(0,1)) = 0.5
}

SubShader {
Tags {
"RenderType"="TransparentCutout"
}
LOD 80
Pass {
Name "Default"
CGPROGRAM
#pragma vertex vert
#pragma fragment frag
#pragma multi_compile_fwdbase
#include "UnityCG.cginc"
#include "Lighting.cginc"
#pragma multi_compile_fwdbase
#include "AutoLight.cginc"
sampler2D _MainTex;
float4 _MainTex_ST;
float4 _Tint;
fixed _Brightness;
fixed4 _Light;
fixed _Contrast;
fixed _Cutoff;
struct v2f {
float4 pos : SV_POSITION;
float2 texcoord : TEXCOORD1;
float3 normal : NORMAL;
};
v2f vert(appdata_base v) {
v2f o;
o.pos = UnityObjectToClipPos (v.vertex);
o.texcoord = TRANSFORM_TEX(v.texcoord, _MainTex);
o.normal = normalize(mul(float4(v.normal, 0.0), unity_WorldToObject).xyz);

return o;
}
fixed4 frag(v2f i) : SV_TARGET {

float4x4 modelMatrix = unity_ObjectToWorld;

float3 normalDirection = normalize(i.normal);

float4 col = tex2D(_MainTex, i.texcoord) * _Tint;
if (col.a < _Cutoff) discard;

float3 lightColor = _LightColor0.rgb * _Brightness;
float3 greyCol = (col.r + col.g + col.b) / 3.0f;
float3 realCol = lerp(col, greyCol, -_Contrast);

return fixed4(realCol.xyz * lightColor + _Light.xyz, 1.0);

}
ENDCG
}
Pass {
Blend SrcAlpha OneMinusSrcAlpha
Name "ShadowCatcher"
Tags { "LightMode" = "ForwardBase" }
CGPROGRAM
#pragma vertex vert
#pragma fragment frag Standard fullforwardshadows alphatest:_Cutoff addshadow
#pragma multi_compile_fwdbase
#include "UnityCG.cginc"
#include "Lighting.cginc"
#pragma multi_compile_fwdbase
#include "AutoLight.cginc"
sampler2D _MainTex;
float4 _MainTex_ST;
fixed _Shadows;
fixed _Cutoff;
struct v2f {
float4 pos : SV_POSITION;
float2 texcoord : TEXCOORD1;
LIGHTING_COORDS(2,3)
};
v2f vert(appdata_base v) {
v2f o;
o.pos = UnityObjectToClipPos (v.vertex);
TRANSFER_VERTEX_TO_FRAGMENT(o);
o.texcoord = TRANSFORM_TEX(v.texcoord, _MainTex);
return o;
}
fixed4 frag(v2f i) : SV_TARGET {

float atten = LIGHT_ATTENUATION(i);
half4 c;
c.rgb = 0;
c.a = (1 - atten) * _Shadows;
if (tex2D(_MainTex, i.texcoord).a < _Cutoff) c.a = 0;
return c;
}
ENDCG
}
}

}
```
Here one with only one:

```
Shader "Cutout" {

Properties {
_MainTex ("Base (RGB)", 2D) = "white" {}
_Tint ("Tint", Color) = (1, 1, 1, 1)
_Brightness ("Brightness", Range(0,4)) = 1.25
_Light ("Light", Color) = (0, 0, 0, 1)
_Shadows ("Shadows", Range(0,1)) = 0.75
_Contrast ("Contrast", Range(-1,1)) = 0.0
_Cutoff ("Alpha cutoff", Range(0,1)) = 0.5
}

SubShader {
Tags {
"RenderType"="TransparentCutout"
"Queue"="AlphaTest"
"IgnoreProjector"="True"
}
LOD 80
Pass {
Name "ShadowCatcher"
Tags { "LightMode" = "ForwardBase" }
CGPROGRAM
#pragma vertex vert
#pragma fragment frag
#pragma multi_compile_fwdbase
#include "UnityCG.cginc"
#include "Lighting.cginc"
#pragma multi_compile_fwdbase
#include "AutoLight.cginc"
sampler2D _MainTex;
float4 _MainTex_ST;
float4 _Tint;
fixed _Brightness;
fixed _Shadows;
fixed4 _Light;
fixed _Contrast;
fixed _Cutoff;
struct v2f {
float4 pos : SV_POSITION;
float2 texcoord : TEXCOORD1;
float3 normal : NORMAL;
LIGHTING_COORDS(2,3)
};
v2f vert(appdata_base v) {
v2f o;
o.pos = UnityObjectToClipPos (v.vertex);
TRANSFER_VERTEX_TO_FRAGMENT(o);
o.texcoord = TRANSFORM_TEX(v.texcoord, _MainTex);
o.normal = normalize(mul(float4(v.normal, 0.0), unity_WorldToObject).xyz);

return o;
}
fixed4 frag(v2f i) : SV_TARGET {

float4x4 modelMatrix = unity_ObjectToWorld;

float3 normalDirection = normalize(i.normal);

float4 col = tex2D(_MainTex, i.texcoord) * _Tint;
if (col.a < _Cutoff) discard;

float shadowFac =
_Brightness *
(1.0 - (1.0 - LIGHT_ATTENUATION(i)) * _Shadows);

float3 lightColor = _LightColor0.rgb * shadowFac;
float3 greyCol = (col.r + col.g + col.b) / 3.0f;
float3 realCol = lerp(col, greyCol, -_Contrast);

return fixed4(realCol.xyz * lightColor + _Light.xyz, 1.0);

}
ENDCG
}

}

}
```

Both results look the same; in both cases I don't see the shadows thrown onto the object, but the shadows thrown onto objects hidden by the object with this shader. This is what I would expect for the transparent parts.

If I add a custom shadow caster pass, which does never discard the result, everything catches the shadow, even the transparent parts...

Any idea how to fix this?

 

I finally found my problem. The custom shadow caster pass was wrong.