// Author: Blastom
// 仅用于摄像机拍摄UI面板的RenderTexture
// 该材质会向颜色Buffer中写入Alpha值，因此不会在没有背景时被剔除
Shader "Zhanyou/Particles/ParticleAlphaDissolve"
{
	Properties
	{
		_TintColor ("Tint Color", Color) = (0.5, 0.5, 0.5, 0.5)
		_MainTex ("Particle Texture", 2D) = "white" {}
		// 溶解贴图，RGB为颜色，A为溶解开始数值
		_DissolveTex ("Dissolve Tex", 2D) = "white" {}
		// 部分溶解的渐变区域值
		_DissolveFade ("Dissolve Fade", Range(0, 1)) = 0.1
		// 完全溶解的Alpha数值
		_DissolveEnd ("Dissolve End", Range(0, 1)) = 0.5
	}
	Category {
		Tags { "Queue"="Transparent" "IgnoreProjector"="True" "RenderType"="Transparent" "PreviewType"="Plane" }
		//BlendOp Add, Max
		Blend SrcAlpha OneMinusSrcAlpha//, One One
		Cull Off
		Lighting Off
		ZWrite Off
		//ColorMask RGB
		
		SubShader {
			Pass {
				CGPROGRAM
				#pragma vertex vert
				#pragma fragment frag
				#pragma multi_compile_fog
				#pragma multi_compile_particles
				#include "UnityCG.cginc"
	
				sampler2D _MainTex;
				fixed4 _TintColor;
				
				struct appdata_t {
					float4 vertex : POSITION;
					fixed4 color : COLOR;
					float2 texcoord : TEXCOORD0;
				};
				
				struct v2f {
					float4 vertex : SV_POSITION;
					fixed4 color : COLOR;
					float2 texcoord : TEXCOORD0;
					float2 dissolveCoord : TEXCOORD1;
					UNITY_FOG_COORDS(2)
				};
				
				uniform float4 _MainTex_ST;
				uniform sampler2D _DissolveTex;
				uniform half4 _DissolveTex_ST;
				uniform half _DissolveFade;
				uniform half _DissolveEnd;

				v2f vert (appdata_t v)
				{
					v2f o;
					o.vertex = UnityObjectToClipPos(v.vertex);
					o.color = v.color;
					o.texcoord = TRANSFORM_TEX(v.texcoord, _MainTex);
					o.dissolveCoord = TRANSFORM_TEX(v.texcoord, _DissolveTex);
					UNITY_TRANSFER_FOG(o, o.vertex);
					return o;
				}
				fixed4 frag (v2f i) : SV_Target
				{
					// 对齐AlphaWriteAlpha，不乘以2
					fixed4 col = i.color * _TintColor * tex2D(_MainTex, i.texcoord);
					fixed4 dissolve = tex2D(_DissolveTex, i.dissolveCoord);
					if (dissolve.a <= _DissolveEnd + _DissolveFade)
					{
						float alpha = max(0.0, (dissolve.a - _DissolveEnd) / _DissolveFade);
						col.a *= alpha;
						col.rgb = lerp(lerp(dissolve.rgb, col.rgb, alpha), dissolve.rgb, alpha * alpha);
					}
					UNITY_APPLY_FOG(i.fogCoord, col);
					return col;
				}
				ENDCG 
			}
		}	
	}
}