效果展示：

原模型：

一、简单分析

卡通渲染又叫非真实渲染（None-Physical Rendering-NPR）,一般日漫里的卡通风格有几个特点：

1.人物有描边

2.有明显的阴影分界线，没有太平滑的过渡

以下就根据这两点来实现卡渲效果；

二、描边

1.法线外扩

实现描边方式多种，比如卷积区分边界；

这里使用更简单的两个Pass，一个只用纯色画背面，利用法线外扩顶点，根据深度的不同这个纯色的背面会被显示出来，同时又不会遮挡正面；

Pass
{
    Tags {"LightMode"="ForwardBase"}
	//裁剪正面，只画背面
    Cull Front
    
    CGPROGRAM
    #pragma vertex vert
    #pragma fragment frag
    #include "UnityCG.cginc"

    half _OutlineWidth;
    half4 _OutLineColor;

    struct a2v 
    {
        float4 vertex : POSITION;
        float3 normal : NORMAL;
        float2 uv : TEXCOORD0;
        float4 vertColor : COLOR;
        float4 tangent : TANGENT;
    };

    struct v2f
    {
        float4 vertColor : TEXCOORD0;
        float4 pos : SV_POSITION;
    };

    v2f vert (a2v v) 
    {
        v2f o;
        UNITY_INITIALIZE_OUTPUT(v2f, o);
        
        //顶点沿着法线方向外扩
        o.pos = UnityObjectToClipPos(float4(v.vertex.xyz + v.normal * _OutlineWidth * 0.1 ,1));
        
        o.vertColor = fixed4(v.vertColor.rgb,1.0);
        return o;
    }

    half4 frag(v2f i) : SV_TARGET 
    {
        return half4(_OutLineColor.rgb * i.vertColor.rgb, 0);
    }
    ENDCG
}

2.细节处理（坑）

摄像机远近边缘线粗细不同

由于世界坐标系下做外扩，摄像机里物体远近会影响法线外扩的多少；

解决方案，在NDC坐标系下法线外扩；

//顶点着色器替换以下代码
float4 pos = UnityObjectToClipPos(v.vertex);

//摄像机空间法线
float3 viewNormal = mul((float3x3)UNITY_MATRIX_IT_MV, v.normal.xyz);

//将法线变换到NDC空间，投影空间*W分量
float3 ndcNormal = normalize(TransformViewToProjection(viewNormal.xyz)) * pos.w;

//xy两方向外扩
pos.xy += 0.01 * _OutlineWidth * ndcNormal.xy * v.vertColor.a;
o.pos = pos;

上下和左右边缘线粗细不同

NDC空间是正方形，而视口宽高比是长方体，导致描边上下和左右的粗细不统一；

解放方案，根据屏幕宽高比缩放法线再外扩；

//将近裁剪面右上角位置的顶点变换到观察空间
//unity_CameraInvProjection摄像机矩阵逆矩阵，UNITY_NEAR_CLIP_VALUE近截面值，DX：0，OpenGL-1.0;_ProjectionParams.y摄像机近截面
float4 nearUpperRight = mul(unity_CameraInvProjection, float4(1, 1, UNITY_NEAR_CLIP_VALUE, _ProjectionParams.y));

//求得屏幕宽高比
float aspect = abs(nearUpperRight.y / nearUpperRight.x);
ndcNormal.x *= aspect;

顶点重合法线不连续

模型顶点重合时会出现多条法线，在不同的面上法线不同导致描边不连续；

解决方案，修改模型顶点数据，同顶点多条法线求平均值；

需要和美工协商修改模型数据，这里写了脚本临时修改模型数据；

public class PlugTangentTools
{
    [MenuItem("Tools/模型平均法线写入切线数据")]
    public static void WirteAverageNormalToTangentToos()
    {
        MeshFilter[] meshFilters = Selection.activeGameObject.GetComponentsInChildren();
        foreach (var meshFilter in meshFilters)
        {
            Mesh mesh = meshFilter.sharedMesh;
            WirteAverageNormalToTangent(mesh);
        }

        SkinnedMeshRenderer[] skinMeshRenders = Selection.activeGameObject.GetComponentsInChildren();
        foreach (var skinMeshRender in skinMeshRenders)
        {
            Mesh mesh = skinMeshRender.sharedMesh;
            WirteAverageNormalToTangent(mesh);
        }
        Debug.Log("重合顶点平均法线写入成功");
    }

    private static void WirteAverageNormalToTangent(Mesh mesh)
    {
        var averageNormalHash = new Dictionary();
        for (var j = 0; j < mesh.vertexCount; j++)
        {
            if (!averageNormalHash.ContainsKey(mesh.vertices[j]))
            {
                averageNormalHash.Add(mesh.vertices[j], mesh.normals[j]);
            }
            else
            {
                averageNormalHash[mesh.vertices[j]] =
                    (averageNormalHash[mesh.vertices[j]] + mesh.normals[j]).normalized;
            }
        }

        var averageNormals = new Vector3[mesh.vertexCount];
        for (var j = 0; j < mesh.vertexCount; j++)
        {
            averageNormals[j] = averageNormalHash[mesh.vertices[j]];
        }

        var tangents = new Vector4[mesh.vertexCount];
        for (var j = 0; j < mesh.vertexCount; j++)
        {
            tangents[j] = new Vector4(averageNormals[j].x, averageNormals[j].y, averageNormals[j].z, 0);
        }
        mesh.tangents = tangents;
    }
}

细节处理前后对比：

ps：利用模型顶点的四个通道RGBA——对描边粗细显影相机距离缩放进行精细控制，需要美工配合；

三、着色

1.减少色阶

二分法

将有阴影和没阴影的地方做明显的区分；

half4 frag(v2f i) : SV_TARGET 
{
    half4 col = 1;
    half4 mainTex = tex2D(_MainTex, i.uv);
    half3 viewDir = normalize(_WorldSpaceCameraPos.xyz - i.worldPos.xyz);
    half3 worldNormal = normalize(i.worldNormal);
    half3 worldLightDir = normalize(_WorldSpaceLightPos0.xyz);

    //半兰伯特光照模型
    half halfLambert = dot(worldNormal, worldLightDir) * 0.5 + 0.5;
    
    //_ShadowRange区分阴影范围，_ShadowSmooth控制分界线的柔和程度，求出ramp值（百分比）
    half ramp = smoothstep(0, _ShadowSmooth, halfLambert - _ShadowRange);

    //根据ramp值插值取样，将阴影和main颜色混合
    half3 diffuse = lerp(_ShadowColor, _MainColor, ramp);
    diffuse *= mainTex;
    col.rgb = _LightColor0 * diffuse;
    return col;
}

Ramp贴图

使用明显分界的色阶图来取样，使阴影有明显的分界线；

逻辑和二分一样，只是多加个几个色阶；

//_ShadowRange范围取样Ramp贴图
half ramp =  tex2D(_RampTex, float2(saturate(halfLambert - _ShadowRange), 0.5)).r;

?

高光色阶

卡渲高光和阴影一样，和周围色块有明显的分界线；

half3 specular = 0;
half3 halfDir = normalize(worldLightDir + viewDir);
half NdotH = max(0, dot(worldNormal, halfDir));
//_SpecularGloss控制高光光泽度
half SpecularSize = pow(NdotH, _SpecularGloss);

//_SpecularRange高光范围，_SpecularMulti强度，在范围内显示高光有明显分界
if (SpecularSize >= 1 - _SpecularRange)
{
	specular = _SpecularMulti * _SpecularColor;
}

ilmTexture贴图

《GUILTY GEAR Xrd》中使用的方法，又叫Threshold贴图；

贴图的R通道控制漫反射的阴影阈值，G通道控制高光强度，B通道控制高光范围;

需要和美工配合，没贴图就不测了；

总之万物皆可用贴图来传递信息，rgba代表什么意思可以自行做各种trick；

half4 frag (v2f i) : SV_Target
{
	half4 col = 0;
	half4 mainTex = tex2D (_MainTex, i.uv);
    //取样ilmTexture
	half4 ilmTex = tex2D (_IlmTex, i.uv);
	half3 viewDir = normalize(_WorldSpaceCameraPos.xyz - i.worldPos.xyz);
	half3 worldNormal = normalize(i.worldNormal);
	half3 worldLightDir = normalize(_WorldSpaceLightPos0.xyz);
	
    //漫反射+阴影
	half3 diffuse = 0;
	half halfLambert = dot(worldNormal, worldLightDir) * 0.5 + 0.5;
    //g通道控制高光强度
	half threshold = (halfLambert + ilmTex.r) * 0.5;
	half ramp = saturate(_ShadowRange  - threshold); 
	ramp =  smoothstep(0, _ShadowSmooth, ramp);
	diffuse = lerp(_MainColor, _ShadowColor, ramp);
	diffuse *= mainTex.rgb;

	half3 specular = 0;
	half3 halfDir = normalize(worldLightDir + viewDir);
	half NdotH = max(0, dot(worldNormal, halfDir));
	half SpecularSize = pow(NdotH, _SpecularGloss);
    //b通道控制高光遮罩
	half specularMask = ilmTex.b;
	if (SpecularSize >= 1 - specularMask * _SpecularRange)
	{
        //g控制高光强度
		specular = _SpecularMulti * (ilmTex.g) * _SpecularColor;
	}

	col.rgb = (diffuse + specular) * _LightColor0.rgb;
	return col;
}

【翻译】西川善司「实验做出的游戏图形」「GUILTY GEAR Xrd -SIGN-」中实现的「纯卡通动画的实时3D图形」的秘密，前篇（1）

【翻译】西川善司「实验做出的游戏图形」「GUILTY GEAR Xrd -SIGN-」中实现的「纯卡通动画的实时3D图形」的秘密，前篇（2）

【翻译】西川善司的「实验做出的游戏图形」「GUILTY GEAR Xrd -SIGN-」中实现的「纯卡通动画的实时3D图形」的秘密，后篇

2.边缘泛光

三渲二加点边缘泛光会增加立体感，让画质更真实；效果如下；

_RimMin、_RimMax控制边缘泛光范围；

smoothstep使过渡平缓；再乘以RimColor，alpha控制强度；

half f =  1.0 - saturate(dot(viewDir, worldNormal));
half rim = smoothstep(_RimMin, _RimMax, f);
rim = smoothstep(0, _RimSmooth, rim);
half3 rimColor = rim * _RimColor.rgb *  _RimColor.a;
col.rgb = (diffuse + specular + rimColor) * _LightColor0.rgb;

3.mask遮罩图

用一张贴图来修正边缘泛光的效果；

边缘光的计算使用的是法线点乘视线。在物体的法线和视线垂直的时候，边缘光会很强。在球体上不会有问题，但是在一些有平面的物体，当平面和视线接近垂直的时候，会导致整个平面都有边缘光。这会让一些不该有边缘光的地方出现边缘光。

4.屏幕后效

post-processing官方组件中有bloom效果；

原理：提取图像中较亮区域，存储在纹理中，使用高斯模糊模拟光线扩散效果，将该纹理和原图像混合；过程比较复杂，后面写屏幕后期效果再分析吧；

完整Shader:

Shader "Unlit/CelRenderFull"
{
	Properties
	{
		_MainTex ("MainTex", 2D) = "white" {}
        _IlmTex ("IlmTex", 2D) = "white" {}

		[Space(20)]
		_MainColor("Main Color", Color) = (1,1,1)
		_ShadowColor ("Shadow Color", Color) = (0.7, 0.7, 0.7)
		_ShadowSmooth("Shadow Smooth", Range(0, 0.03)) = 0.002
		_ShadowRange ("Shadow Range", Range(0, 1)) = 0.6

		[Space(20)]
		_SpecularColor("Specular Color", Color) = (1,1,1)
		_SpecularRange ("Specular Range",  Range(0, 1)) = 0.9
        _SpecularMulti ("Specular Multi", Range(0, 1)) = 0.4
		_SpecularGloss("Sprecular Gloss", Range(0.001, 8)) = 4

		[Space(20)]
		_OutlineWidth ("Outline Width", Range(0, 1)) = 0.24
        _OutLineColor ("OutLine Color", Color) = (0.5,0.5,0.5,1)
			
		[Space(20)]
		_RimMin	("imMin",float) = 1.0
		_RimMax	("RimMax",float) = 2.0
		_RimSmooth("RimSmooth",Range(0.0,1))=0.5
		_RimColor("RimColor",Color) = (1,1,1,1)
	}

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

			CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
			#pragma multi_compile_fwdbase
			
			#include "UnityCG.cginc"
			#include "Lighting.cginc"
            #include "AutoLight.cginc"

            sampler2D _MainTex; 
			float4 _MainTex_ST;
            sampler2D _IlmTex; 
			float4 _IlmTex_ST;

			half3 _MainColor;
			half3 _ShadowColor;
			half _ShadowSmooth;
			half _ShadowRange;
			
			half3 _SpecularColor;
			half _SpecularRange;
        	half _SpecularMulti;
			half _SpecularGloss;

			half _RimMin;		
			half _RimMax;
			half _RimSmooth;
			fixed4 _RimColor;

			struct a2v
			{
				float4 vertex : POSITION;
				float2 uv : TEXCOORD0;
				float3 normal : NORMAL;
			};

			struct v2f
			{
				float4 pos : SV_POSITION;
				float2 uv : TEXCOORD0;	
				float3 worldNormal : TEXCOORD1;
				float3 worldPos : TEXCOORD2; 
			};
			
			v2f vert (a2v v)
			{
				v2f o = (v2f)0;
				o.pos = UnityObjectToClipPos(v.vertex);
				o.uv = TRANSFORM_TEX(v.uv, _MainTex);
				o.worldNormal = UnityObjectToWorldNormal(v.normal);
				o.worldPos = mul(unity_ObjectToWorld, v.vertex).xyz;
				return o;
			}
			
			half4 frag (v2f i) : SV_Target
			{
				half4 col = 0;
				half4 mainTex = tex2D (_MainTex, i.uv);
				half4 ilmTex = tex2D (_IlmTex, i.uv);
				half3 viewDir = normalize(_WorldSpaceCameraPos.xyz - i.worldPos.xyz);
				half3 worldNormal = normalize(i.worldNormal);
				half3 worldLightDir = normalize(_WorldSpaceLightPos0.xyz);

				half3 diffuse = 0;
				half halfLambert = dot(worldNormal, worldLightDir) * 0.5 + 0.5;
				half threshold = (halfLambert + ilmTex.g) * 0.5;
				half ramp = saturate(_ShadowRange  - threshold); 
				ramp =  smoothstep(0, _ShadowSmooth, ramp);
				diffuse = lerp(_MainColor, _ShadowColor, ramp);
				diffuse *= mainTex.rgb;

				half3 specular = 0;
				half3 halfDir = normalize(worldLightDir + viewDir);
				half NdotH = max(0, dot(worldNormal, halfDir));
				half SpecularSize = pow(NdotH, _SpecularGloss);
				half specularMask = ilmTex.b;
				if (SpecularSize >= 1 - specularMask * _SpecularRange)
				{
					specular = _SpecularMulti * (ilmTex.r) * _SpecularColor;
				}

				half f =  1.0 - saturate(dot(viewDir, worldNormal));
				half rim = smoothstep(_RimMin, _RimMax, f);
				rim = smoothstep(0, _RimSmooth, rim);
				half3 rimColor = rim * _RimColor.rgb *  _RimColor.a;
				col.rgb = (diffuse + specular + rimColor) * _LightColor0.rgb;

				return col;
			}
			ENDCG
		}

        Pass
	    {
	        Tags {"LightMode"="ForwardBase"}
			 
            Cull Front
            
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #include "UnityCG.cginc"

            half _OutlineWidth;
            half4 _OutLineColor;

            struct a2v 
	        {
                float4 vertex : POSITION;
                float3 normal : NORMAL;
                float2 uv : TEXCOORD0;
                float4 vertColor : COLOR;
                float4 tangent : TANGENT;
            };

            struct v2f

	        {
                float4 vertColor : TEXCOORD0;
                float4 pos : SV_POSITION;
            };


            v2f vert (a2v v) 
	        {
                v2f o;
		        UNITY_INITIALIZE_OUTPUT(v2f, o);
                
                float4 pos = UnityObjectToClipPos(v.vertex);
                float3 viewNormal = mul((float3x3)UNITY_MATRIX_IT_MV, v.tangent.xyz);
                float3 ndcNormal = normalize(TransformViewToProjection(viewNormal.xyz)) * pos.w;
				

                float4 nearUpperRight = mul(unity_CameraInvProjection, float4(1, 1, UNITY_NEAR_CLIP_VALUE, _ProjectionParams.y));
                float aspect = abs(nearUpperRight.y / nearUpperRight.x);
                ndcNormal.x *= aspect;

                pos.xy += 0.01 * _OutlineWidth * ndcNormal.xy * v.vertColor.a;
                o.pos = pos;
                o.vertColor = fixed4(v.vertColor.rgb,1.0);
                return o;
            }

            half4 frag(v2f i) : SV_TARGET 
	        {
                return half4(_OutLineColor.rgb * i.vertColor.rgb, 0);
            }
            ENDCG
        }
	}
	FallBack Off
}