When we should use the program variants

Unity Engine
1

hi guys

Can anyone help to explain what does program variant do? When we must add it into the code and when it’s not necessary .

Thanks in advance

 Pass{
            Tags{"LightMode"="ForwardBase"}

            CGPROGRAM

            #pragma vertex vert
            #pragma fragment frag

            #include "Lighting.cginc"
            #include "AutoLight.cginc"

            #pragma multi_compile_fwdbase

            sampler2D _MainTex;
            float4 _MainTex_ST;
            fixed4 _Color;
            samplerCUBE _CubeMap;
            fixed _ReflectAmount;
            fixed4 _ReflectColor;

            struct a2v{
                float4 vertex:POSITION;
                fixed3 normal:NORMAL;
                float4 texcoord:TEXCOORD0;

            };
            struct v2f{
                float4 pos:SV_POSITION;
                float3 worldPos:TEXCOORD5;
                float2 uv:TEXCOORD0;
                fixed3 worldNormal:TEXCOORD1;
                fixed3 worldViewDir:TEXCOORD2;
                fixed3 reflDir:TEXCOORD3;
                fixed3 worldLightDir:TEXCOORD6;
                SHADOW_COORDS(4)
            };

            v2f vert(a2v v){
                v2f o;
                o.pos=UnityObjectToClipPos(v.vertex);
                o.worldPos=mul(unity_ObjectToWorld,v.vertex).xyz;
                o.uv=v.vertex.xy*_MainTex_ST.xy+_MainTex_ST.zw;
                o.worldNormal=mul(v.normal,(float3x3)unity_WorldToObject);
                o.worldViewDir=_WorldSpaceCameraPos-v.vertex.xyz;
                o.reflDir=reflect(-o.worldViewDir,o.worldNormal);
                o.worldLightDir=_WorldSpaceLightPos0.xyz;

                TRANSFER_SHADOW(o);
                return o;

            }

            fixed4 frag(v2f i):SV_Target{
                fixed3 worldNormal=normalize(i.worldNormal);
                fixed3 worldLightDir=normalize(i.worldLightDir);
                fixed3 albedo=tex2D(_MainTex,i.uv).rgb*_Color.rgb;
                fixed3 reflColor=texCUBE(_CubeMap,i.reflDir).rgb*_ReflectColor.rgb;
                fixed3 ambient=UNITY_LIGHTMODEL_AMBIENT.xyz*albedo;
                UNITY_LIGHT_ATTENUATION(atten,i,i.worldPos);
                fixed3 diffuse=_LightColor0.rgb*albedo*max(0,dot(worldNormal,worldLightDir));
                return fixed4(ambient+lerp(diffuse,reflColor,_ReflectAmount),1.0)*atten;
            }
            ENDCG
2

Hi!

In the v2f struct you have worldLightDir that uses TEXCOORD4 and SHADOW_COORD that also uses TEXCOORD4.
Change either one to 6 (an unused one) and you should be good.

3

thanks for reminding, I’ve changed the number.
and I want to ask when i must add the #pragma multi_compile_fwdbase and when it’s not so necessary. cause I found the code can be run well without it.

4