// Unity built-in shader source. Copyright (c) 2016 Unity Technologies. MIT license (see license.txt)

Shader "Mirza Beig/Particles/Distance Fade/Additive"
{
Properties 
{
	_TintColor("Tint Color", Color) = (0.5,0.5,0.5,0.5)
	_MainTex("Particle Texture", 2D) = "white" {}

	_InvFade("Soft Particles Factor", Range(0.01,3.0)) = 1.0

	_FadeMin("Fade Min", Range(0.0, 10.0)) = 1.0
	_FadeMax("Fade Max", Range(0.0, 10.0)) = 2.0
}

Category {
	Tags { "Queue"="Transparent" "IgnoreProjector"="True" "RenderType"="Transparent" "PreviewType"="Plane" }
	Blend SrcAlpha One
	ColorMask RGB
	Cull Off Lighting Off ZWrite Off
	
	SubShader {
		Pass {
		
			CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag
			#pragma target 2.0
			#pragma multi_compile_particles
			#pragma multi_compile_fog

			#include "UnityCG.cginc"

			sampler2D _MainTex;
			fixed4 _TintColor;
			
			struct appdata_t {
				float4 vertex : POSITION;
				fixed4 color : COLOR;
				float2 texcoord : TEXCOORD0;
				UNITY_VERTEX_INPUT_INSTANCE_ID
			};

			struct v2f {
				float4 vertex : SV_POSITION;
				fixed4 color : COLOR;
				float2 texcoord : TEXCOORD0;
				UNITY_FOG_COORDS(1)

				#ifdef SOFTPARTICLES_ON

				float4 projPos : TEXCOORD2;

				#endif
				UNITY_VERTEX_OUTPUT_STEREO
			};
			
			float4 _MainTex_ST;

			float _FadeMin;
			float _FadeMax;

			v2f vert (appdata_t v)
			{
				v2f o;
				UNITY_SETUP_INSTANCE_ID(v);
				UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(o);
				o.vertex = UnityObjectToClipPos(v.vertex);

				#ifdef SOFTPARTICLES_ON

				o.projPos = ComputeScreenPos (o.vertex);
				COMPUTE_EYEDEPTH(o.projPos.z);

				#endif

				o.color = v.color;				
				
				float4 viewPos = mul(UNITY_MATRIX_MV, v.vertex);

				float distance = -viewPos.z - _ProjectionParams.y;
				float alpha = (distance - _FadeMin) / _FadeMax;

				alpha = min(alpha, 1.0);

				o.color.a *= alpha;

				o.texcoord = TRANSFORM_TEX(v.texcoord,_MainTex);
				UNITY_TRANSFER_FOG(o,o.vertex);
				return o;
			}

			UNITY_DECLARE_DEPTH_TEXTURE(_CameraDepthTexture);
			float _InvFade;
			
			fixed4 frag (v2f i) : SV_Target
			{
				#ifdef SOFTPARTICLES_ON

				float sceneZ = LinearEyeDepth (SAMPLE_DEPTH_TEXTURE_PROJ(_CameraDepthTexture, UNITY_PROJ_COORD(i.projPos)));
				float partZ = i.projPos.z;
				float fade = saturate (_InvFade * (sceneZ-partZ));
				i.color.a *= fade;

				#endif
				
				fixed4 col = 2.0f * i.color * _TintColor * tex2D(_MainTex, i.texcoord);

				UNITY_APPLY_FOG_COLOR(i.fogCoord, col, fixed4(0,0,0,0)); // fog towards black due to our blend mode
				return col;
			}
			ENDCG 
		}
	}	
}
}