Shader "Custom/Standard_Single_Flash"
{
    Properties
    {
        _Color ("Color", Color) = (1,1,1,1)
        _MainTex ("Albedo (RGB)", 2D) = "white" {}
        _Glossiness ("Smoothness", Range(0,1)) = 0.5
        _Metallic ("Metallic", Range(0,1)) = 0.0
        _FlashPos ("Flash Position",Color) =(0,0,0,0)
        _FlashColor("Flash Color",Color) = (0,0,0,1)
        _FlashStartTime("Flash Start", float) = 0
        _FlashEndTime("Flash End", float) = 0
        _FlashRange("Flash Range",float) = 10.0
    }
    SubShader
    {
        Tags { "RenderType"="Opaque" }
        LOD 200

        CGPROGRAM
        // Physically based Standard lighting model, and enable shadows on all light types
        #pragma surface surf Standard fullforwardshadows

        // Use shader model 3.0 target, to get nicer looking lighting
        #pragma target 3.0

        sampler2D _MainTex;

        struct Input
        {
            float2 uv_MainTex;
            float3 worldPos;
            float3 worldNormal;
        };

        half    _Glossiness;
        half    _Metallic;
        fixed4  _Color;
        fixed4  _FlashPos;
        fixed4  _FlashColor;
        fixed   _FlashStartTime;
        fixed   _FlashEndTime;
        fixed   _FlashRange;

        // Add instancing support for this shader. You need to check 'Enable Instancing' on materials that use the shader.
        // See https://docs.unity3d.com/Manual/GPUInstancing.html for more information about instancing.
        // #pragma instancing_options assumeuniformscaling
        UNITY_INSTANCING_BUFFER_START(Props)
            // put more per-instance properties here
        UNITY_INSTANCING_BUFFER_END(Props)

        void surf (Input IN, inout SurfaceOutputStandard o)
        {
            //Animated intensity value controlled from script
            fixed flashIntensity =  1.0-clamp((_Time.y - _FlashStartTime)/(_FlashEndTime - _FlashStartTime),0.0,1.0);
            //_FlashPos coming from script as well
            fixed3 lightDir =_FlashPos.xyz - IN.worldPos;
            float dist = length(lightDir);

            //Fairly standard NDotL

            float nl = max(0, dot(IN.worldNormal,lightDir));
            //All the different attenuation formulas Ive played around with:
            //float atten = 1.0/dist * 0.5;
            //float inverseRange = _FlashRange;
            //float atten = 1.0-(dist / (1.0 / inverseRange));
            //float atten=1.0/(1.0+0.1*dist+0.01*dist*dist);
            //float att = clamp(1.0 - dist/_FlashRange, 0.0, 1.0);
            //att *= att;

            float att = 1.0 / (1.0 + 0 * dist + 1.0 * dist * dist);
            float3 flashTerm = nl* _FlashColor * flashIntensity * att;
            fixed4 c = tex2D (_MainTex, IN.uv_MainTex) * _Color;

            o.Albedo = c.rgb;
            o.Metallic = _Metallic;
            o.Smoothness = _Glossiness;
            o.Alpha = c.a;
            o.Emission = flashTerm;
        }
        ENDCG
    }
    FallBack "Diffuse"
}