Why does this code work without any "Pass{}" expressions? And is there a way to add shadow collections?

Questions & Answers
1

Hey guys! I don’t know much about shaders, but I found this shader on the internet. I turned culling off for both of the passes. My character consists of some sprites that are flipped, and I wanted them all to be visible and to cast shadows on the same side. I only vaguely understand the code. Just enough to get it working for my purposes. So, my question is two-fold:

  1. Why are there no Pass{} expressions? Aren’t you supposed to surround each pass with one? Or is that optional?

  2. How do I add shadow collections to the shader? I tried adding this section of code, but it didn’t do anything:

    // Pass to render object as a shadow collector
    Pass {
    Name “ShadowCollector”
    Tags { “LightMode” = “ShadowCollector” }

           Cull Off//new 
       Lighting On //new
        Fog {Mode Off}
        ZWrite On ZTest LEqual
 
        CGPROGRAM
        #pragma vertex vert
        #pragma fragment frag
        #pragma fragmentoption ARB_precision_hint_fastest
        #pragma multi_compile_shadowcollector
 
        #define SHADOW_COLLECTOR_PASS
        #include "UnityCG.cginc"
 
        struct appdata {
            float4 vertex : POSITION;
        };
 
        struct v2f {
            V2F_SHADOW_COLLECTOR;
        };
 
        v2f vert (appdata v)
        {
            v2f o;
            TRANSFER_SHADOW_COLLECTOR(o)
            return o;
        }
 
        fixed4 frag (v2f i) : COLOR
        {
            SHADOW_COLLECTOR_FRAGMENT(i)
        }
        ENDCG
 
    }

Shader “Sprites/Bumped Diffuse both sides with Shadows 2”
{
Properties
{
[PerRendererData] _MainTex (“Base (RGB)”, 2D) = “white” {}
_BumpMap (“Normalmap”, 2D) = “bump” {}
_Color (“Tint”, Color) = (1,1,1,1)
[MaterialToggle] PixelSnap (“Pixel snap”, Float) = 0
_Cutoff (“Alpha Cutoff”, Range (0,1)) = 0.5

     }
 
     SubShader
     {
         Tags
         { 
             "Queue"="Transparent" 
             "IgnoreProjector"="True" 
             "RenderType"="TransparentCutOut" 
             "PreviewType"="Plane"
             "CanUseSpriteAtlas"="True"
             
         }
         LOD 300
 
         // Render back faces first
         Cull Off
         Lighting On
         ZWrite Off
         Fog { Mode Off }
         
         CGPROGRAM
         #pragma surface surf Lambert alpha vertex:vert addshadow alphatest:_Cutoff 
         #pragma multi_compile DUMMY PIXELSNAP_ON 
 
         sampler2D _MainTex;
         sampler2D _BumpMap;
         fixed4 _Color;
         float _ScaleX;
 
         struct Input
         {
             float2 uv_MainTex;
             float2 uv_BumpMap;
             fixed4 color : COLOR;
         };
         
         void vert (inout appdata_full v, out Input o)
         {
             #if defined(PIXELSNAP_ON) && !defined(SHADER_API_FLASH)
             v.vertex = UnityPixelSnap (v.vertex);
             #endif
             float3 normal = v.normal;
             
             v.normal = float3(0,0,-1);
             v.tangent =  float4(1, 0, 0, 1);
             
             UNITY_INITIALIZE_OUTPUT(Input, o);
             o.color += _Color;
         }
 
         void surf (Input IN, inout SurfaceOutput o)
         {
             fixed4 c = tex2D(_MainTex, IN.uv_MainTex) * IN.color;
             o.Albedo = c.rgb;
             o.Alpha = c.a;
             o.Normal = UnpackNormal(tex2D(_BumpMap, IN.uv_BumpMap));
         }
         ENDCG
         
         // Now render front faces first
         Cull Off
         Lighting On
         ZWrite Off
         Fog { Mode Off }
         
         CGPROGRAM
         #pragma surface surf Lambert alpha vertex:vert addshadow alphatest:_Cutoff 
         #pragma multi_compile DUMMY PIXELSNAP_ON 
 
         sampler2D _MainTex;
         sampler2D _BumpMap;
         fixed4 _Color;
         float _ScaleX;
 
         struct Input
         {
             float2 uv_MainTex;
             float2 uv_BumpMap;
             fixed4 color: COLOR;
         };
         
         void vert (inout appdata_full v, out Input o)
         {
             #if defined(PIXELSNAP_ON) && !defined(SHADER_API_FLASH)
             v.vertex = UnityPixelSnap (v.vertex);
             #endif
             float3 normal = v.normal;
             
             v.normal = float3(0,0,1);
             v.tangent =  float4(1, 0, 0, 1);
             
             UNITY_INITIALIZE_OUTPUT(Input, o);
             o.color += _Color;
         }
 
         void surf (Input IN, inout SurfaceOutput o)
         {
             fixed4 c = tex2D(_MainTex, IN.uv_MainTex) * IN.color;
             o.Albedo = c.rgb;
             o.Alpha = c.a;
             o.Normal = UnpackNormal(tex2D(_BumpMap, IN.uv_BumpMap));
             o.Normal.z *= -1;
         }
         ENDCG
         

   
	    // Pass to render object as a shadow collector
	    Pass {
	        Name "ShadowCollector"
	        Tags { "LightMode" = "ShadowCollector" }
	       
	       Cull Off//new 
	       Lighting On //new
	        Fog {Mode Off}
	        ZWrite On ZTest LEqual
	 
	        CGPROGRAM
	        #pragma vertex vert
	        #pragma fragment frag
	        #pragma fragmentoption ARB_precision_hint_fastest
	        #pragma multi_compile_shadowcollector
	 
	        #define SHADOW_COLLECTOR_PASS
	        #include "UnityCG.cginc"
	 
	        struct appdata {
	            float4 vertex : POSITION;
	        };
	 
	        struct v2f {
	            V2F_SHADOW_COLLECTOR;
	        };
	 
	        v2f vert (appdata v)
	        {
	            v2f o;
	            TRANSFER_SHADOW_COLLECTOR(o)
	            return o;
	        }
	 
	        fixed4 frag (v2f i) : COLOR
	        {
	            SHADOW_COLLECTOR_FRAGMENT(i)
	        }
	        ENDCG
	 
	    }
	    
	    
         
     }
 
 Fallback "Transparent/Cutout/Diffuse"
 }
2

You don’t define explicit passes for surface shaders - Unity defines them when it compiles the shader.
To add shadows, you simply include the addshadow option to the #pragma that declares the surface shader function - Unity - Manual: Writing Surface Shaders.