转成unity可用的 shader

将给定的Cocos Creator Shader转换为Unity可用的Shader需要进行一些调整和重构。以下是基于提供的Cocos Creator Shader代码生成的一个Unity Shader示例：

### Unity Shader 示例

Shader "Custom/CocosCreatorShader"
{
    Properties
    {
        _MainTex ("Albedo Map", 2D) = "white" {}
        _Albedo ("Albedo Color", Color) = (1,1,1,1)
        _TilingOffset ("Tiling Offset", Vector) = (1,1,0,0)
        _AlphaThreshold ("Alpha Threshold", Range(0,1)) = 0.5
        _Occlusion ("Occlusion", Range(0,1)) = 1.0
        _Roughness ("Roughness", Range(0,1)) = 0.8
        _Metallic ("Metallic", Range(0,1)) = 0.6
        _SpecularIntensity ("Specular Intensity", Range(0,1)) = 0.5
        _NormalStrength ("Normal Strength", Range(0,1)) = 1.0
        _Emissive ("Emissive Color", Color) = (0,0,0,1)
        _EmissiveScale ("Emissive Scale", Vector) = (1,1,1,1)
        _NormalMap ("Normal Map", 2D) = "bump" {}
        _PBRMap ("PBR Map", 2D) = "white" {}
        _MetallicRoughnessMap ("Metallic Roughness Map", 2D) = "white" {}
        _OcclusionMap ("Occlusion Map", 2D) = "white" {}
        _EmissiveMap ("Emissive Map", 2D) = "white" {}
    }

    SubShader
    {
        Tags { "RenderType"="Opaque" }
        LOD 200

        Pass
        {
            Name "FORWARD"
            Tags { "LightMode"="ForwardBase" }

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

            struct appdata
            {
                float4 vertex : POSITION;
                float3 normal : NORMAL;
                float4 tangent : TANGENT;
                float2 uv : TEXCOORD0;
                float2 uv1 : TEXCOORD1;
                fixed4 color : COLOR;
            };

            struct v2f
            {
                float4 pos : SV_POSITION;
                float3 worldPos : TEXCOORD0;
                float3 worldNormal : TEXCOORD1;
                float3 worldTangent : TEXCOORD2;
                float3 worldBitangent : TEXCOORD3;
                float2 uv : TEXCOORD4;
                float2 uv1 : TEXCOORD5;
                fixed4 color : COLOR;
                SHADOW_COORDS(6)
            };

            sampler2D _MainTex;
            sampler2D _NormalMap;
            sampler2D _PBRMap;
            sampler2D _MetallicRoughnessMap;
            sampler2D _OcclusionMap;
            sampler2D _EmissiveMap;

            float4 _MainTex_ST;
            float4 _TilingOffset;
            float4 _Albedo;
            float _AlphaThreshold;
            float _Occlusion;
            float _Roughness;
            float _Metallic;
            float _SpecularIntensity;
            float _NormalStrength;
            float4 _Emissive;
            float4 _EmissiveScale;

            v2f vert (appdata v)
            {
                v2f o;
                o.pos = UnityObjectToClipPos(v.vertex);
                o.worldPos = mul(unity_ObjectToWorld, v.vertex).xyz;
                o.worldNormal = UnityObjectToWorldNormal(v.normal);
                o.worldTangent = UnityObjectToWorldDir(v.tangent.xyz);
                o.worldBitangent = cross(o.worldNormal, o.worldTangent) * v.tangent.w;
                o.uv = TRANSFORM_TEX(v.uv, _MainTex) * _TilingOffset.xy + _TilingOffset.zw;
                o.uv1 = TRANSFORM_TEX(v.uv1, _MainTex) * _TilingOffset.xy + _TilingOffset.zw;
                o.color = v.color;
                TRANSFER_SHADOW(o);
                return o;
            }

            fixed4 frag (v2f i) : SV_Target
            {
                fixed4 baseColor = _Albedo;
                baseColor *= tex2D(_MainTex, i.uv);

                if (baseColor.a < _AlphaThreshold)
                    discard;

                float3 normal = i.worldNormal;
                if (_NormalStrength > 0)
                {
                    float3 normalMap = UnpackNormal(tex2D(_NormalMap, i.uv));
                    normal = normalize(i.worldTangent * normalMap.x * _NormalStrength +
                                      i.worldBitangent * normalMap.y * _NormalStrength +
                                      i.worldNormal * normalMap.z);
                }

                float4 pbr = float4(_Occlusion, _Roughness, _Metallic, _SpecularIntensity);
                if (tex2D(_PBRMap, i.uv).r > 0)
                {
                    pbr.x *= tex2D(_PBRMap, i.uv).r;
                    pbr.y *= tex2D(_PBRMap, i.uv).g;
                    pbr.z *= tex2D(_PBRMap, i.uv).b;
                    pbr.w *= tex2D(_PBRMap, i.uv).a;
                }

                if (tex2D(_MetallicRoughnessMap, i.uv).r > 0)
                {
                    pbr.z *= tex2D(_MetallicRoughnessMap, i.uv).b;
                    pbr.y *= tex2D(_MetallicRoughnessMap, i.uv).g;
                }

                if (tex2D(_OcclusionMap, i.uv).r > 0)
                {
                    pbr.x *= tex2D(_OcclusionMap, i.uv).r;
                }

                float3 emissive = _Emissive.rgb * _EmissiveScale.xyz;
                if (tex2D(_EmissiveMap, i.uv).rgb > 0)
                {
                    emissive *= tex2D(_EmissiveMap, i.uv).rgb;
                }

                UNITY_LIGHT_ATTENUATION(attenuation, i, i.worldPos)

                fixed4 finalColor = baseColor * attenuation;
                finalColor.rgb += emissive;

                return finalColor;
            }
            ENDCG
        }

        Pass
        {
            Name "SHADOWCASTER"
            Tags { "LightMode"="ShadowCaster" }

            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #pragma multi_compile_shadowcaster
            #include "UnityCG.cginc"

            struct appdata
            {
                float4 vertex : POSITION;
                float2 uv : TEXCOORD0;
                float2 uv1 : TEXCOORD1;
            };

            struct v2f
            {
                V2F_SHADOW_CASTER;
                float2 uv : TEXCOORD1;
                float2 uv1 : TEXCOORD2;
            };

            sampler2D _MainTex;
            float4 _MainTex_ST;
            float4 _TilingOffset;
            float _AlphaThreshold;

            v2f vert (appdata v)
            {
                v2f o;
                TRANSFER_SHADOW_CASTER_NORMALOFFSET(o)
                o.uv = TRANSFORM_TEX(v.uv, _MainTex) * _TilingOffset.xy + _TilingOffset.zw;
                o.uv1 = TRANSFORM_TEX(v.uv1, _MainTex) * _TilingOffset.xy + _TilingOffset.zw;
                return o;
            }

            float4 frag (v2f i) : SV_Target
            {
                fixed4 baseColor = tex2D(_MainTex, i.uv);
                if (baseColor.a < _AlphaThreshold)
                    discard;

                SHADOW_CASTER_FRAGMENT(i)
            }
            ENDCG
        }
    }

    FallBack "Diffuse"
}

### 解释

1. **Properties**:
- 定义了与Cocos Creator Shader中对应的属性，如 `_MainTex`, `_Albedo`, `_TilingOffset` 等。

2. **SubShader**:
- 包含两个Pass：一个用于前向渲染（`FORWARD`），另一个用于阴影投射（`SHADOWCASTER`）。

3. **Vertex Shader (`vert`)**:
- 处理顶点变换，计算世界坐标、法线、切线和副切线，并传递纹理坐标和颜色。

4. **Fragment Shader (`frag`)**:
- 计算基础颜色、法线、PBR参数、自发光等，并应用阴影衰减。
- 使用 `discard` 关键字处理透明度测试。

5. **ShadowCaster Pass**:
- 用于生成阴影贴图，处理透明度测试并丢弃不满足条件的片段。

这个Unity Shader应该能够实现类似Cocos Creator Shader的效果。你可以根据具体需求进一步调整和优化。