Games 101 - Shading

Shader "Custom/Blinn-Phong"
{
    Properties
    {
        _BaseColor ("Base Color", Color) = (1.0, 1.0, 1.0, 1.0)
        _BaseMap ("Main Texture", 2D) = "white"{}
        _SpecColor("Specular Color", Color) = (1.0, 1.0, 1.0, 1.0)
        _Smoothness("Smoothness", range(8, 256)) = 20
    }
    SubShader
    {
        Tags {
            "RenderType"="Opaque" 
            "RenderPipeline"="UniversalRenderPipeline" 
            "LightMode" = "UniversalForward"
            "ShaderModel"="4.5"
        }
        LOD 100
        Pass
        {
            HLSLPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            
            #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"
            #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Lighting.hlsl"
            
            struct Attributes
            {
                half4 positionOS : POSITION;
                half3 normal : NORMAL;
                half4 tangetOS : TANGENT;
                half2 uv : TEXCOORD0;
            };

            struct Varyings
            {
                half4 positionCS : SV_POSITION;
                half3 positionWS : POSITION_WS;
                half2 uv : TEXCOORD0;
                half3 normalWS : NORMAL_WS;
            };

            TEXTURE2D(_BaseMap);
            SAMPLER(sampler_BaseMap);
            
            CBUFFER_START(UnityPerMaterial)
                half4 _BaseMap_ST;
                half4 _BaseColor;
                half4 _SpecColor;
                half _Smoothness;
            CBUFFER_END
            
            Varyings vert (Attributes IN)
            {
                const VertexPositionInputs vertex_position_inputs = GetVertexPositionInputs(IN.positionOS);
                const VertexNormalInputs vertex_normal_inputs = GetVertexNormalInputs(IN.normal);

                Varyings OUT;
                OUT.positionWS = vertex_position_inputs.positionWS;
                OUT.positionCS = vertex_position_inputs.positionCS;
                OUT.uv = TRANSFORM_TEX(IN.uv, _BaseMap);
                OUT.normalWS = vertex_normal_inputs.normalWS;
                return OUT;
            }
            
            half4 frag (Varyings IN) : SV_Target
            {
                Light mainLight = GetMainLight();
                half3 lightColor = mainLight.color;
                half3 lightDir = normalize(mainLight.direction);
                half3 lightAtten = mainLight.distanceAttenuation;
                // diffuse
                half3 albedo = SAMPLE_TEXTURE2D(_BaseMap, sampler_BaseMap, IN.uv) * _BaseColor;
                half kd = albedo;
                half light = lightColor * lightAtten;
                half ndotL = max(0, dot(IN.normalWS, lightDir));
                half3 diffuse = kd * light * ndotL;
                // specular
                half ks = 1 - kd;
                half3 viewDirWS = normalize(GetCameraPositionWS() - IN.positionWS);
                half3 halfDir = normalize(viewDirWS + lightDir);
                half nDotH = max(0, dot(halfDir, IN.normalWS));
                half3 specular = ks * light * pow(nDotH, _Smoothness) * saturate(_SpecColor);
                // Ambient
                half3 ambient = 0.1;
                // Combine
                half4 finalColor = half4(ambient + diffuse + specular, 1.0);
                return finalColor;
            }
            ENDHLSL
        }
    }
}