shader 渐变半透明效果

// Upgrade NOTE: replaced 'mul(UNITY_MATRIX_MVP,*)' with 'UnityObjectToClipPos(*)'


Shader "Custom/zhengshuang" {
Properties
{
_MainTex ("Texture", 2D) = "white" {}
_AlphaLX("RangeAlphaLX",Float) = 0
_AlphaRX("RangeAlphaRX",Float) = 1
_AlphaTY("RangeAlphaTY",Float) = 1
_AlphaBY("RangeAlphaBY",Float) = 0
_AlphaPower("Power",Float) = 0 //透明度变化范围
}
SubShader
{
Tags { "RenderType"="Transparent" }
Blend SrcAlpha OneMinusSrcAlpha
Cull Back
Pass
{
CGPROGRAM
#pragma vertex vert
#pragma fragment frag

#include "UnityCG.cginc"


struct appdata
{
float4 vertex : POSITION;
float2 uv : TEXCOORD0;
};


struct v2f
{
float2 uv : TEXCOORD0;
float4 vertex : SV_POSITION;
};


sampler2D _MainTex;
float4 _MainTex_ST;
float _AlphaPower;
sampler2D _AlphaTex;
float _AlphaLX;
float _AlphaRX;
float _AlphaTY;
float _AlphaBY;


v2f vert (appdata v)
{
v2f o;
o.vertex = UnityObjectToClipPos(v.vertex);
o.uv = TRANSFORM_TEX(v.uv, _MainTex);
return o;
}
//此方法取自Unity默认Sprite的Shader
fixed4 SampleSpriteTexture (float2 uv)
{
fixed4 color = tex2D (_MainTex, uv);


#if ETC1_EXTERNAL_ALPHA
// get the color from an external texture (usecase: Alpha support for ETC1 on android)
color.a = tex2D (_AlphaTex, uv).r;
#endif //ETC1_EXTERNAL_ALPHA


return color;
}


fixed4 frag (v2f i) : SV_Target
{
// sample the texture
fixed4 col = SampleSpriteTexture(i.uv);
//利用透明度阈值和uv坐标的差来计算透明的程度和是否控制其半透
//四个方向只是对坐标的取值和正反方向不同，原理一致
fixed alphalx = col.a * lerp(1,_AlphaPower,(_AlphaLX-i.uv.x));
col.a = saturate(lerp(alphalx,col.a,step(_AlphaLX,i.uv.x)));


fixed alpharx = col.a * lerp(1,_AlphaPower,(i.uv.x-_AlphaRX));
col.a = saturate(lerp(col.a,alpharx,step(_AlphaRX,i.uv.x)));


fixed alphaby = col.a * lerp(1,_AlphaPower,(_AlphaBY-i.uv.y));
col.a = saturate(lerp(alphaby,col.a,step(_AlphaBY,i.uv.y)));


fixed alphaty = col.a * lerp(1,_AlphaPower,(i.uv.y-_AlphaTY));
col.a = saturate(lerp(col.a,alphaty,step(_AlphaTY,i.uv.y)));


return col;
}
ENDCG
}
}
}