Max或maya导出的模型经常会有单面材质的效果，大概率是法线或是单面材质的问题。可以用双面shader解决。发现一个比较好用的，转载码一下。原地址：https://blog.csdn.net/liang_704959721/article/details/88681768

shader代码如下：

Shader "yh/DoubleSide" {
 
    Properties     
    {    
		_MainTex ("MainTex (RGB)", 2D) = "white" {}	//颜色贴图
 
		_MainTint ("Main Color", Color) = (0.5, 0.5, 0.5, 1)
		_MainTintPower ("Main Color Power", Float ) = 1.2
 
		_XRayColor ("XRay Color", Color) = (1, 1, 1, 1) //(0.435, 0.851, 1, 0.419)    
		_XRayPower ("XRay Power", Float) = 0.5
 
		//透明度裁剪（模型头发之类的）
		_AlphaCutoff ("Alpha cutoff", Float) = 0.5
 
		//受击发光颜色
		_HitColor ("Hit Color", Color) = (0.6,0.6,0.6,1)
		_HitColorWidth ("Hit Color Width", Float) = 0.8
		//是否被击0没有被击 1被击中，正常要设置为0（制作材质球时打到1可调受击颜色，然后调到0即可正常显示颜色）
		_IsHit ("Is Hit", Range(0, 1)) = 0
 
		//是否经济模式，经济模式不透明裁剪
		_IsECHO ("Is ECHO", Range(0, 1)) = 0
 
    }    
        
    SubShader     
    {    
		Tags { "Queue"="Geometry+200" "RenderType"="Opaque" }
		Fog { Mode off }  
		//LOD 200
		
        Blend SrcAlpha OneMinusSrcAlpha    
 
 
        Pass {
       		Lighting Off
 
			Cull Off 
 
 
 
			Blend SrcAlpha  OneMinusSrcAlpha
 
            CGPROGRAM
                #pragma vertex vert
                #pragma fragment frag
                #include "UnityCG.cginc"
 
                struct appdata 
                {
                    float4 vertex : POSITION;
                    float3 normal : NORMAL;
                    float2 texcoord : TEXCOORD0;
                };
 
                struct v2f 
                {
                    float4 pos : SV_POSITION;
                    float2 uv : TEXCOORD0;
                    fixed3 color : COLOR;
                };
 
                uniform float4 _MainTex_ST;
                uniform fixed4 _HitColor;
                float _HitColorWidth;
				fixed _AlphaCutoff;
				float _IsHit;
				float _MainTintPower;
				float _IsECHO;
 
 
                v2f vert (appdata_base v) {
                    v2f o;
                    o.pos = UnityObjectToClipPos (v.vertex);
 
					if(_IsHit==1)
					{
						float3 viewDir = normalize(ObjSpaceViewDir(v.vertex));
						float dotProduct = 1 - dot(v.normal, viewDir);
						o.color = smoothstep(1 - _HitColorWidth, 1.0, dotProduct);
						o.color *= _HitColor;
					}
 
					if (_IsHit==0)
					{
						o.color = 0;
					}
 
                    o.uv = v.texcoord.xy;
                    return o;
                }
 
                uniform sampler2D _MainTex;
                uniform fixed4 _MainTint;
 
                fixed4 frag(v2f i) : COLOR {
 
                    fixed4 texcol = tex2D(_MainTex, i.uv);
                    texcol *= _MainTint;
					//texcol *= _MainTintPower * 2;
                    texcol.rgb += i.color;
//texcol.a=0;
					if(_IsECHO == 0)
					{
						clip(texcol.a - _AlphaCutoff);
					}
 
                    return texcol;
                }
            ENDCG
        }
    }    
}