Unity Shader实现太空中的大气层效果

Shader "Custom/Atmosphere Glow"
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	Properties
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		//大气层的颜色
		_AtmoColor("Glow Color", Color) = (1,1,1,1)
		//大气层反射效果的强化量
		_InnterRingFactor("Glow Factor", Float) = 5
		//大气层相对于地表的偏移
		_Offset("Vertex Offset", Float) = 0
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	SubShader
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		Tags
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			"IgnoreProjector" = "True"
			"Queue" = "Transparent"
			"RenderType" = "Transparent"
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		Pass
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			Blend One One
			AlphaTest Greater 0.1
			ColorMask RGBA
			Cull Back Lighting Off ZWrite Off Fog｛ Color(0,0,0,0) ｝
			CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag
			#pragma glsl
			#pragma target 3.0
			uniform float _InnterRingFactor;
			uniform float4 _AtmoColor;
			uniform float _Offset;
			struct VertexInput
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				float4 vertex : POSITION;
				float3 normal : NORMAL;
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			struct VertexOutput
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				float4 pos : SV_POSITION;
				float4 posWorld : TEXCOORD0;
				float3 normalDir : TEXCOORD1;
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			VertexOutput vert(VertexInput v)
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				VertexOutput o;
				//获得顶点的发现方向
				o.normalDir = normalize(mul(unity_ObjectToWorld,float4(v.normal, 0)).xyz);
				//对原来的顶点进行偏移
				v.vertex.xyz += (_Offset*v.normal);
				//在世界中的顶点信息
				o.posWorld = mul(unity_ObjectToWorld, v.vertex);
				//转换后得到偏移后的顶点信息
				o.pos = mul(UNITY_MATRIX_MVP, v.vertex);
				return o;
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			float4 frag(VertexOutput i) : COLOR
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				//视角方向
				float3 viewDirection = normalize(_WorldSpaceCameraPos.xyz - i.posWorld.xyz);
				//项目里没有使用光源，shader中模拟（0,0,0）点为太阳光照（点光源）
				float3 lightDirection = normalize((0,0,0) - i.posWorld.xyz);
				float ndl = dot(i.normalDir, lightDirection);
				float ndv = dot(i.normalDir, viewDirection);
				//实现的效果为内侧描边
				//这里当ndv为正数时，指数越大，效果越小，ndv为负数时1-ndv为大于1的数，指数越大，效果越强
				float3 innerRing = saturate(_AtmoColor.xyz * pow(1 - ndv,_InnterRingFactor)) ;
				//光源方向参与到运算中
				float3 finalColor = saturate(pow(ndl + max(0.2, dot(-lightDirection, viewDirection)), 3)) * (innerRing * 2) ;
				return float4(finalColor, 1);
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		ENDCG
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