shader 素描画效果实现

素描效果基本原理：先将物体进行描边画出轮廓，计算物体的漫反射部分，漫反射越暗表明颜色越暗，然后根据漫反射的值来设置采样贴图的权重。

采样贴图：

Shader "Unlit/Sketch"
{
	Properties
	{
		_Color("Color",Color) = (1,1,1,1)
		//贴图平铺系数
	    _TileFactor("TileFactor", Range(0, 10)) = 1
		_Hatch0("Hatch0",2D)="white"{}
	    _Hatch1("Hatch1",2D) = "white"{}
	    _Hatch2("Hatch2",2D) = "white"{}
	    _Hatch3("Hatch3",2D) = "white"{}
	    _Hatch4("Hatch4",2D) = "white"{}
	    _Hatch5("Hatch5",2D) = "white"{}
		//描边系数
		_OutlineFactor("OutlineFactor",Range(0.0,0.1))=0.01
	}
	SubShader
	{
		Tags{ "Queue" = "Transparent" }
		//描边使用两个Pass，第一个pass沿法线挤出一点，只输出描边的颜色
		Pass
		{
			//剔除正面，只渲染背面
			Cull Front
			//关闭深度写入
			ZWrite Off
			//控制深度偏移，描边pass远离相机一些，防止与正常pass穿插
			Offset 1,1

			CGPROGRAM
            #include "UnityCG.cginc"
            #pragma vertex vert
            #pragma fragment frag
		    float _OutlineFactor;

		    struct v2f
		    {
			    float4 pos : SV_POSITION;
		    };

		    v2f vert(appdata_full v)
		    {
			    v2f o;
			    o.pos = UnityObjectToClipPos(v.vertex);
			    //将法线方向转换到视空间
			    float3 vnormal = mul((float3x3)UNITY_MATRIX_IT_MV, v.normal);
			    //将视空间法线xy坐标转化到投影空间
			    float2 offset = TransformViewToProjection(vnormal.xy);
			    //在最终投影阶段输出进行偏移操作
			    o.pos.xy += offset * _OutlineFactor;
			    return o;
		    }

		    fixed4 frag(v2f i) : SV_Target
		    {
			    return float4(0,0,0,1);
		    }
			ENDCG
		}
		

		Pass
		{
			CGPROGRAM
            #include "UnityCG.cginc"
            #include "Lighting.cginc"
			//使用阴影需添加
            #include "AutoLight.cginc"
			#pragma vertex vert
			#pragma fragment frag
			//使主要平行光产生阴影
            #pragma multi_compile_fwdbase

			

			float4 _Color;
	        float _TileFactor;
			sampler2D _Hatch0;
			sampler2D _Hatch1;
			sampler2D _Hatch2;
			sampler2D _Hatch3;
			sampler2D _Hatch4;
			sampler2D _Hatch5;

			struct v2f
			{
				float2 uv : TEXCOORD0;
				float4 vertex : SV_POSITION;
				//6张依次加深的贴图
				float3 hatchWeights0:TEXCOORD1;
				float3 hatchWeights1:TEXCOORD2;
				//声明阴影
				SHADOW_COORDS(4)
				float3 worldPos:TEXCOORD3;
			};
		
			v2f vert (appdata_full v)
			{
				v2f o;
				o.vertex = UnityObjectToClipPos(v.vertex);
				//平铺系数越大，显示的贴图越密集
				o.uv = v.texcoord* _TileFactor;
				float3 worldLightDir = normalize(WorldSpaceLightDir(v.vertex));
				float3 worldNormal = UnityObjectToWorldNormal(v.normal);
				//漫反射
				float diffuse = max(0, dot(worldLightDir, worldNormal));
				o.worldPos = mul(unity_ObjectToWorld, v.vertex).xyz ;
				//六张图片的权重
				o.hatchWeights0 = float3(0, 0, 0);
				o.hatchWeights1 = float3(0, 0, 0);
				//根据漫反射值计算权重，漫反射越暗，线条越密集
				float hatchFactor = diffuse * 7.0;
				if (hatchFactor > 6.0) {
				}
				else if (hatchFactor > 5.0) {
					o.hatchWeights0.x = hatchFactor - 5.0;
				}
				else if (hatchFactor > 4.0) {
					o.hatchWeights0.x = hatchFactor - 4.0;
					o.hatchWeights0.y = 1.0 - o.hatchWeights0.x;
				}
				else if (hatchFactor > 3.0) {
					o.hatchWeights0.y = hatchFactor - 3.0;
					o.hatchWeights0.z = 1.0 - o.hatchWeights0.y;
				}
				else if (hatchFactor > 2.0) {
					o.hatchWeights0.z = hatchFactor - 2.0;
					o.hatchWeights1.x = 1.0 - o.hatchWeights0.z;
				}
				else if (hatchFactor > 1.0) {
					o.hatchWeights1.x = hatchFactor - 1.0;
					o.hatchWeights1.y = 1.0 - o.hatchWeights1.x;
				}
				else {
					o.hatchWeights1.y = hatchFactor;
					o.hatchWeights1.z = 1.0 - o.hatchWeights1.y;
				}
				//把计算的阴影传到fragment中
				TRANSFER_SHADOW(o);
				return o;
			}
			
			fixed4 frag (v2f i) : SV_Target
			{ 
				float4 hatchTex0 = tex2D(_Hatch0, i.uv) * i.hatchWeights0.x;
				float4 hatchTex1 = tex2D(_Hatch1, i.uv) * i.hatchWeights0.y;
				float4 hatchTex2 = tex2D(_Hatch2, i.uv) * i.hatchWeights0.z;
				float4 hatchTex3 = tex2D(_Hatch3, i.uv) * i.hatchWeights1.x;
				float4 hatchTex4 = tex2D(_Hatch4, i.uv) * i.hatchWeights1.y;
				float4 hatchTex5 = tex2D(_Hatch5, i.uv) * i.hatchWeights1.z;
				//漫反射暗色部分权重越大，白色越少
				float4 whiteColor = float4(1, 1, 1, 1)*(1 - i.hatchWeights0.x - i.hatchWeights0.y - i.hatchWeights0.z - i.hatchWeights1.x - i.hatchWeights1.y - i.hatchWeights1.z);
				float4 hatchColor = hatchTex0 + hatchTex1 + hatchTex2 + hatchTex3 + hatchTex4 + hatchTex5+ whiteColor;
				//使物体接受阴影
				UNITY_LIGHT_ATTENUATION(atten, i, i.worldPos);
				return float4(hatchColor.rgb*_Color.rgb*atten, 1.0);
			}
			ENDCG
		}		
	}
}

最终效果：