Shader "Custom/PhotoGlass"
{
	Properties
	{
		[Slider(0.1)] _F0("F0", Range(0.0, 1.0)) = 0.02
		[Slider(0.1)] _ThicknessFactor("Thickness", Range(0.0, 1.0)) = 0.3
		[Slider(0.1)] _RefractionIndex("RefractionIndex", Range(1.0, 3.0)) = 1.33
		_CubeMap("Cube Map", Cube) = "white" {}
	}

	SubShader
	{
		Tags{ "Queue" = "Transparent" "RenderType" = "Transparent" }

		// Forward Base
		Pass
		{
			Tags{"LightMode" = "ForwardBase"}

			Blend SrcAlpha OneMinusSrcAlpha
			ColorMask RGB
			Cull Back
			// ZWrite Off

			CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag
			#pragma multi_compile_fwdbase

			#include "UnityCG.cginc"
			#include "AutoLight.cginc"

			struct appdata
			{
				float4 vertex   : POSITION;
				half3 normal    : NORMAL;
			};

			struct v2f
			{
				float4 vertex   : SV_POSITION;
				half3 viewDir : TEXCOORD1;
				half3 normal : TEXCOORD2;
				half3 lightDir : TEXCOORD3;
				float4 worldPos : TEXCOORD4;
				LIGHTING_COORDS(5, 6)
			};

			UNITY_DECLARE_TEXCUBE(_CubeMap);
			float _F0;
			float _ThicknessFactor;
			float _RefractionIndex;
			uniform fixed4 _LightColor0;

			v2f vert(appdata v)
			{
				v2f o;
				o.vertex = UnityObjectToClipPos(v.vertex);
				o.viewDir = normalize(WorldSpaceViewDir(v.vertex));
				o.normal = normalize(UnityObjectToWorldNormal(v.normal));
				o.lightDir = normalize(WorldSpaceLightDir(v.vertex));
				o.worldPos = mul(unity_ObjectToWorld, o.vertex);

				TRANSFER_VERTEX_TO_FRAGMENT(o);

				return o;
			}

			fixed4 frag(v2f i) : SV_Target
			{
				half atten = LIGHT_ATTENUATION(i);
				half3 ambient = UNITY_LIGHTMODEL_AMBIENT;
				half4 lightColor = _LightColor0;

				float fresnel = _F0 + (1.0h - _F0) * pow(1.0h - dot(i.viewDir, i.normal) + 0.3, 5);
				fresnel = clamp(fresnel, 0, 1);
				half3 reflDir = reflect(-i.viewDir, i.normal);
				half3 refrDir = refract(-i.viewDir, i.normal, 1.0 / _RefractionIndex);
				half3 dir = lerp(reflDir, refrDir, lerp(0, 1 - fresnel, _ThicknessFactor));

				fixed4 color = UNITY_SAMPLE_TEXCUBE_LOD(_CubeMap, dir, 0);
				color.rgb = DecodeHDR(color, unity_SpecCube0_HDR);
				color.rgb = (color * lightColor * atten) + ambient;
				color.a = lerp(fresnel, 1, _ThicknessFactor);
				return color;
			}
			ENDCG
		}

		// Forward Add
		Pass
		{
			Tags{"LightMode" = "ForwardAdd"}

			Blend SrcAlpha One
			ColorMask RGB
			Cull Back
			// ZWrite Off

			CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag
			#pragma multi_compile_fwdadd

			#include "UnityCG.cginc"
			#include "AutoLight.cginc"

			struct appdata
			{
				float4 vertex   : POSITION;
				half3 normal    : NORMAL;
			};

			struct v2f
			{
				float4 vertex   : SV_POSITION;
				half3 viewDir : TEXCOORD1;
				half3 normal : TEXCOORD2;
				half3 worldPos: TEXCOORD3;
				LIGHTING_COORDS(4, 5)
			};

			UNITY_DECLARE_TEXCUBE(_CubeMap);
			float _F0;
			float _ThicknessFactor;
			float _RefractionIndex;
			uniform fixed4 _LightColor0;

			v2f vert(appdata v)
			{
				v2f o;
				o.vertex = UnityObjectToClipPos(v.vertex);
				o.viewDir = normalize(WorldSpaceViewDir(v.vertex));
				o.normal = normalize(UnityObjectToWorldNormal(v.normal));
				o.worldPos = mul(unity_ObjectToWorld, v.vertex);

				TRANSFER_VERTEX_TO_FRAGMENT(o);

				return o;
			}

			fixed4 frag(v2f i) : SV_Target
			{
				half atten = LIGHT_ATTENUATION(i);
				half4 lightColor = _LightColor0;

				half3 lightDir;
				if (_WorldSpaceLightPos0.w > 0) {
					lightDir = _WorldSpaceLightPos0.xyz - i.worldPos.xyz;
				}
				else {
					lightDir = _WorldSpaceLightPos0.xyz;
				}
				lightDir = normalize(lightDir);

				float fresnel = _F0 + (1.0h - _F0) * pow(1.0h - dot(i.viewDir, i.normal) + 0.3, 5);
				fresnel = clamp(fresnel, 0, 1);
				half3 reflDir = reflect(-i.viewDir, i.normal);
				half3 refrDir = refract(-i.viewDir, i.normal, 1.0 / _RefractionIndex);
				half3 dir = lerp(reflDir, refrDir, lerp(0, 1 - fresnel, _ThicknessFactor));

				fixed4 color = UNITY_SAMPLE_TEXCUBE_LOD(_CubeMap, reflDir, (1 - fresnel));
				color.rgb = DecodeHDR(color, unity_SpecCube0_HDR);
				color.rgb *= dot(i.normal, lightDir);
				color.rgb = color * lightColor * atten;
				color.a = lerp(fresnel, 1, _ThicknessFactor);
				return color;
			}
			ENDCG
		}
	}
}