法线外扩#

基本原理#

原理是渲染两次，第一个 Pass 正常渲染正面，将背面剔除，第二个 Pass 将正面剔除后先将背面顶点沿着法线的方向移动，外扩后再渲染背面，

最后两个 Pass 叠加在一起。

Unity 实现#

渲染正面

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Shader "nekoside/default"
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{
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    Properties
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    {
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        _BaseColor("BaseColor", Color) = (0, 0, 0, 1)
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    }
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    SubShader
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    {
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        Tags
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        {
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            "RenderType" = "Opaque"
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            "Queue" = "Geometry"
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        }
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        // 渲染正面
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        Pass
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        {
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            Cull Back
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            HLSLPROGRAM
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            #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"
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            #pragma vertex vert
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            #pragma fragment frag
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            CBUFFER_START(UnityPerMaterial)
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                half4 _BaseColor;
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            CBUFFER_END
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            struct Attributes
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            {
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                float3 positionOS : POSITION;
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            };
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            struct Varyings
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            {
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                float4 positionHCS : SV_POSITION;
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            };
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            Varyings vert(Attributes IN)
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            {
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                Varyings OUT;
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                OUT.positionHCS = TransformObjectToHClip(IN.positionOS);
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                return OUT;
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            }
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            half4 frag(Varyings IN) : SV_Target
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            {
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                half4 OUT;
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                OUT = half4(_BaseColor.rgba);
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                return OUT;
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            }
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            ENDHLSL
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        }
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    }
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}

渲染背面（描边）

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Shader "nekoside/outline"
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{
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    Properties
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    {
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        _OutlineColor ("Outline Color", Color) = (1, 1, 1, 1)
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        _OutlineWidth ("Outline Width", Range(0, 0.5)) = 0.25
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    }
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    SubShader
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    {
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        Tags
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        {
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            "RenderType" = "Opaque" "Queue" = "Geometry"
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        }
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        // 渲染背面（描边）
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        Pass
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        {
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            Cull Front
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            HLSLPROGRAM
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            #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"
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            #pragma vertex vert
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            #pragma fragment frag
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            CBUFFER_START(UnityPerMaterial)
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                half4 _OutlineColor;
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                float _OutlineWidth;
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            CBUFFER_END
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            struct Attributes
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            {
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                float3 positionOS : POSITION;
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                float3 normalOS : NORMAL;
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            };
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            struct Varyings
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            {
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                float4 positionHCS : SV_POSITION;
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            };
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            Varyings vert(Attributes IN)
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            {
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                Varyings OUT;
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                IN.positionOS += _OutlineWidth * IN.normalOS;
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                OUT.positionHCS = TransformObjectToHClip(IN.positionOS);
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                return OUT;
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            }
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            half4 frag(Varyings IN) : SV_Target
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            {
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                return _OutlineColor;
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            }
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            ENDHLSL
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        }
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    }
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}