hue shift shader, a simple way 简单高效方法

hue shift effect in Photoshop：
http://forum.unity3d.com/threads/hue-saturation-brightness-contrast-shader.260649/

Shader "Craft/Simple Hue"{    Properties {    _Color ("Main Color", Color) = (1,1,1,1)    _MainTex ("Base (RGB)", 2D) = "white" {}    }    SubShader {    Tags {  "RenderType"="Opaque" }    LOD 100    Pass {        CGPROGRAM        #pragma vertex vert          #pragma fragment frag        #pragma target 3.0            #include "UnityCG.cginc"        sampler2D _MainTex;        float4  _Color;        struct appdata {        float4 vertex : POSITION;        float3 texcoord : TEXCOORD0;        };        struct v2f {        float4 pos : SV_POSITION;        float2 uv : TEXCOORD0;            };        v2f vert(appdata v)         {        v2f o;        o.pos = mul(UNITY_MATRIX_MVP, v.vertex);        o.uv = v.texcoord;        return o;        }        fixed4 frag(v2f i) : COLOR        {            float4 tex = tex2D(_MainTex, i.uv);            return fixed4(            tex.r-_Color.r*(2*tex.r-tex.g-tex.b),            tex.g-_Color.g*(2*tex.g-tex.r-tex.b),            tex.b-_Color.b*(2*tex.b-tex.r-tex.g),            tex.a                );        }        ENDCG    }    }}

效果：

ref:
https://dexint.wordpress.com/2015/02/03/awkward-but-a-cheaper-option-instead-of-hue-shift-shader/