[Shader]制作一个电流扩散效果

<1>效果图:需要制作一下（那个LOL选大区不是有个电流扩散的效果吗）

思路：从圆心开始扩散，圆半径随时间递增，UV坐标大于半径剔除，小于半径Alpha衰减

代码：

float2 uv = IN.texcoord.xy;
fixed4 col = IN.color;
//从圆心扩散
float radius = sin(_Time.z / 2 % PI);//值域0-1-0
//float radius = _Time.y/4%0.5;
float2 nor = float2(0.5, 0.5) - uv;
float len = length(nor);//计算向量模长
float dis = len - radius;
//扩散到UV坐标外面时越小alpha越小 [0,-0.5]
if (dis < 0)
col.a = 0.5+dis;
if (col.a > 0)
col.a += 0.2;
if (dis > 0)
col.a = 0;

clip(col.a - 0.01);

源码：

Shader "Tang/UIFlash"
{
Properties
{
[PerRendererData] _MainTex("Sprite Texture", 2D) = "white" {}
_Color("Tint", Color) = (1,1,1,1)

_StencilComp("Stencil Comparison", Float) = 8
_Stencil("Stencil ID", Float) = 0
_StencilOp("Stencil Operation", Float) = 0
_StencilWriteMask("Stencil Write Mask", Float) = 255
_StencilReadMask("Stencil Read Mask", Float) = 255

_ColorMask("Color Mask", Float) = 15

//my member

[Toggle(UNITY_UI_ALPHACLIP)] _UseUIAlphaClip("Use Alpha Clip", Float) = 0
}

SubShader
{
Tags
{
"Queue" = "Transparent"
"IgnoreProjector" = "True"
"RenderType" = "Transparent"
"PreviewType" = "Plane"
"CanUseSpriteAtlas" = "True"
}

Stencil
{
Ref[_Stencil]
Comp[_StencilComp]
Pass[_StencilOp]
ReadMask[_StencilReadMask]
WriteMask[_StencilWriteMask]
}

Cull Off
Lighting Off
ZWrite Off
ZTest[unity_GUIZTestMode]
Blend SrcAlpha OneMinusSrcAlpha
ColorMask[_ColorMask]

Pass
{
Name "Default"
CGPROGRAM
#pragma vertex vert
#pragma fragment frag
#pragma target 2.0

#include "UnityCG.cginc"
#include "UnityUI.cginc"

#pragma multi_compile __ UNITY_UI_ALPHACLIP
#define PI 3.1415926

struct appdata_t
{
float4 vertex : POSITION;
float4 color : COLOR;
float2 texcoord : TEXCOORD0;
UNITY_VERTEX_INPUT_INSTANCE_ID
};

struct v2f
{
float4 vertex : SV_POSITION;
fixed4 color : COLOR;
float2 texcoord : TEXCOORD0;
float4 worldPosition : TEXCOORD1;
UNITY_VERTEX_OUTPUT_STEREO
};

fixed4 _Color;
fixed4 _TextureSampleAdd;
float4 _ClipRect;

v2f vert(appdata_t IN)
{
v2f OUT;
UNITY_SETUP_INSTANCE_ID(IN);
UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(OUT);
OUT.worldPosition = IN.vertex;
OUT.vertex = UnityObjectToClipPos(OUT.worldPosition);

OUT.texcoord = IN.texcoord;

OUT.color = IN.color * _Color;
return OUT;
}

sampler2D _MainTex;

fixed4 frag(v2f IN) : SV_Target
{
float2 uv = IN.texcoord.xy;
fixed4 col = IN.color;
//从圆心扩散
float radius = sin(_Time.z / 2 % PI);
//float radius = _Time.y/4%0.5;
float2 nor = float2(0.5, 0.5) - uv;
float len = length(nor);
float dis = len - radius;
//扩散到UV坐标外面时越小alpha越小 [0,-0.5]
if (dis < 0)
col.a = 0.5+dis;
if (col.a > 0)
col.a += 0.2;

if (dis > 0)
col.a = 0;

clip(col.a - 0.01);

half4 color = (tex2D(_MainTex, uv) + _TextureSampleAdd) * col;
color.a *= UnityGet2DClipping(IN.worldPosition.xy, _ClipRect);

#ifdef UNITY_UI_ALPHACLIP
clip(color.a - 0.001);
#endif

return color;
}
ENDCG
}
}
}

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更多shader效果，请看我的github：https://github.com/tianjiuwan