關於NGUI置灰的方案

網上有很多關於NGUI置灰的方案，核心都是修改shader犧牲一個顏色值實現的。

我們可以直接修改NGUI的shader來避免一些出界的情況。這是一個比較簡單的解決方案，當然也可以創建多個shader來實現。但目前我瞭解到的核心都是用一個值作標識來置灰。

貼代碼：

Shader "Unlit/Transparent Colored"
{
	Properties
	{
		_MainTex ("Base (RGB), Alpha (A)", 2D) = "black" {}
	}
	
	SubShader
	{
		LOD 200

		Tags
		{
			"Queue" = "Transparent"
			"IgnoreProjector" = "True"
			"RenderType" = "Transparent"
		}
		
		Pass
		{
			Cull Off
			Lighting Off
			ZWrite Off
			Fog { Mode Off }
			Offset -1, -1
			Blend SrcAlpha OneMinusSrcAlpha

			CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag			
			#include "UnityCG.cginc"

			sampler2D _MainTex;
			float4 _MainTex_ST;
	
			struct appdata_t
			{
				float4 vertex : POSITION;
				float2 texcoord : TEXCOORD0;
				fixed4 color : COLOR;
			};
	
			struct v2f
			{
				float4 vertex : SV_POSITION;
				half2 texcoord : TEXCOORD0;
				fixed4 color : COLOR;
			};
	
			v2f o;

			v2f vert (appdata_t v)
			{
				o.vertex = mul(UNITY_MATRIX_MVP, v.vertex);
				o.texcoord = v.texcoord;
				o.color = v.color;
				return o;
			}
				
			fixed4 frag (v2f i) : COLOR
			{
				fixed4 col;
				if (i.color.r==0&&i.color.g==0&&i.color.b==0)
				{
					col = tex2D(_MainTex, i.texcoord);
					float grey = dot(col.rgb, float3(0.299, 0.587, 0.114));
					col.rgb = float3(grey, grey, grey);
				}
				else
				{
				col = tex2D(_MainTex, i.texcoord) * i.color;
				}
				
				return col;
			}
			ENDCG
		}
	}

	SubShader
	{
		LOD 100

		Tags
		{
			"Queue" = "Transparent"
			"IgnoreProjector" = "True"
			"RenderType" = "Transparent"
		}
		
		Pass
		{
			Cull Off
			Lighting Off
			ZWrite Off
			Fog { Mode Off }
			Offset -1, -1
			ColorMask RGB
			Blend SrcAlpha OneMinusSrcAlpha
			ColorMaterial AmbientAndDiffuse
			
			SetTexture [_MainTex]
			{
				Combine Texture * Primary
			}
		}
	}
}

核心代碼：

<span style="white-space:pre">				</span>if (i.color.r==0&&i.color.g==0&&i.color.b==0)
				{
					col = tex2D(_MainTex, i.texcoord);
					float grey = dot(col.rgb, float3(0.299, 0.587, 0.114));
					col.rgb = float3(grey, grey, grey);
				}