内置渲染管线中的接受阴影着色器示例

要实现对接受阴影的支持，必须将基础光照通道编译成若干变体，以正确处理“没有阴影的方向光”和“有阴影的方向光”这两种情况。#pragma multi_compile_fwdbase 指令可执行此操作（有关详细信息，请参阅多个着色器变体）。实际上它的功能还不止于此：它还为不同的光照贴图类型编译变体、Enlighten 实时全局光照打开或关闭等。目前我们不需要这些，所以我们将明确跳过这些变体。

然后，为了获得实际的阴影计算，我们将 #include “AutoLight.cginc” 着色器的 include 文件并使用该文件中的 SHADOW_COORDS、TRANSFER_SHADOW 和 SHADOW_ATTENUATION 宏。

下面是着色器：

Shader "Lit/Diffuse With Shadows"
{
    Properties
    {
        [NoScaleOffset] _MainTex ("Texture", 2D) = "white" {}
    }
    SubShader
    {
        Pass
        {
            Tags {"LightMode"="ForwardBase"}
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #include "UnityCG.cginc"
            #include "Lighting.cginc"

            // compile shader into multiple variants, with and without shadows
            // (we don't care about any lightmaps yet, so skip these variants)
            #pragma multi_compile_fwdbase nolightmap nodirlightmap nodynlightmap novertexlight
            // shadow helper functions and macros
            #include "AutoLight.cginc"

            struct v2f
            {
                float2 uv : TEXCOORD0;
                SHADOW_COORDS(1) // put shadows data into TEXCOORD1
                fixed3 diff : COLOR0;
                fixed3 ambient : COLOR1;
                float4 pos : SV_POSITION;
            };
            v2f vert (appdata_base v)
            {
                v2f o;
                o.pos = UnityObjectToClipPos(v.vertex);
                o.uv = v.texcoord;
                half3 worldNormal = UnityObjectToWorldNormal(v.normal);
                half nl = max(0, dot(worldNormal, _WorldSpaceLightPos0.xyz));
                o.diff = nl * _LightColor0.rgb;
                o.ambient = ShadeSH9(half4(worldNormal,1));
                // compute shadows data
                TRANSFER_SHADOW(o)
                return o;
            }

            sampler2D _MainTex;

            fixed4 frag (v2f i) : SV_Target
            {
                fixed4 col = tex2D(_MainTex, i.uv);
                // compute shadow attenuation (1.0 = fully lit, 0.0 = fully shadowed)
                fixed shadow = SHADOW_ATTENUATION(i);
                // darken light's illumination with shadow, keep ambient intact
                fixed3 lighting = i.diff * shadow + i.ambient;
                col.rgb *= lighting;
                return col;
            }
            ENDCG
        }

        // shadow casting support
        UsePass "Legacy Shaders/VertexLit/SHADOWCASTER"
    }
}

看看，现在我们实现了阴影！