// Upgrade NOTE: replaced 'mul(UNITY_MATRIX_MVP,*)' with 'UnityObjectToClipPos(*)'

Shader "Unlit/NormalTangent"
{
    Properties
    {
        _Color("Color Tint", Color) = (1, 1, 1, 1)
        _MainTex("Main Tex", 2D) = "While"{}
        //法线纹理
        _BumpMap("Normal Map", 2D) = "bump"{}
        //控制凹凸程度，为0时意味该法线纹理不会对光照产生任何影响
        _BumpScale("Bump Scale", Float) = 1.0
        _Specular("Specular", Color) = (1,1,1,1)
        _Gloss("Gloss", Range(8.0, 256)) = 20
    }
    SubShader
    {
        Pass{
            Tags{"LightMode" = "ForwardBase"}
            CGPROGRAM

            #pragma vertex vert
            #pragma fragment frag

            #include "Lighting.cginc"

            fixed4 _Color;
            sampler2D _MainTex;
            float4 _MainTex_ST;
            sampler2D _BumpMap;
            float4 _BumpMap_ST;
            float _BumpScale;
            fixed4 _Specular;
            float _Gloss;

            struct a2v{
                float4 vertex : POSITION;
                float3 normal : NORMAL;
                float4 tangent : TANGENT;
                float4 texcoord : TEXCOORD0;
            };

            struct v2f{
                float4 pos : SV_POSITION;
                float4 uv : TEXCOORD0;
                float3 lightDir : TEXCOORD1;
                float3 viewDir : TEXCOORD2;
            };

            v2f vert(a2v v){
                v2f o;
                o.pos = UnityObjectToClipPos(v.vertex);
                o.uv.xy = v.texcoord.xy * _MainTex_ST.xy + _MainTex_ST.zw;
                o.uv.zw = v.texcoord.xy * _BumpMap_ST.xy + _BumpMap_ST.zw;

                TANGENT_SPACE_ROTATION;
                //将光照方向从模型空间转换到切线空间中，ObjSpaceLightDir是内置函数，得到模型空间中的光照
                o.lightDir = mul(rotation, ObjSpaceLightDir(v.vertex)).xyz;
                //将视角方向从模型空间转换到切线空间中，ObjSpaceViewDir是内置函数，得到模型空间中的视角方向
                o.viewDir = mul(rotation, ObjSpaceViewDir(v.vertex)).xyz;
                return o;
            }

            fixed4 frag(v2f i) : SV_Target{
                fixed3 tangentLightDir = normalize(i.lightDir);
                fixed3 tangentViewDir = normalize(i.viewDir);

                fixed4 packedNormal = tex2D(_BumpMap, i.uv.zw);
                fixed3 tangentNormal;

                //如果没有在Unity中把该法线纹理类型设置成Normal map
                //tangentNormal.xy = (packedNormal.xy * 2 - 1) * _BumpScale;
                //tangentNormal.z = sqrt(1.0 - saturate(dot(tangentNormal.xy, tangentNormal.xy)));

                //如果设置了Normal map
                tangentNormal = UnpackNormal(packedNormal);
                tangentNormal.xy *= _BumpScale;
                tangentNormal.z = sqrt(1.0 - saturate(dot(tangentNormal.xy, tangentNormal.xy)));

                fixed3 albedo = tex2D(_MainTex, i.uv).rgb * _Color.rgb;
                fixed3 ambient = UNITY_LIGHTMODEL_AMBIENT.xyz * albedo;
                fixed3 diffuse = _LightColor0.rgb * albedo * max(0, dot(tangentNormal, tangentLightDir));

                fixed3 halfDir = normalize(tangentLightDir + tangentViewDir);
                fixed3 specular = _LightColor0.rgb * _Specular * pow(max(0, dot(tangentNormal, halfDir)), _Gloss);

                return fixed4(ambient + diffuse +specular, 1.0);
            }
            ENDCG
        }
        
    }
    Fallback "Specular"
}