NGUI实现Sprite裁切成圆形或者椭圆形(不完美)

先上效果

有个问题就是，UISprie用的Atlas的公用的材质，无法从当前要绘制的片段shader上获得uv百分比，所以当有其他的Sprite使用相同的Atlas时显示就有问题

其实Mesh是可以接受另外一套uv的，不过目前还没有找到给NGUI造的mesh传另外一套uv的方法。

//代码

using System;
using UnityEngine;
using System.Collections;

public class UIRoundSprite : UISprite 
{
    public float RoundRate = 0.8f;
    protected override void OnUpdate ()
    {
        if(mChanged)
        {
            var atlas = GetAtlasSprite();
            if (null != atlas && null != material)
            {
                 var w = material.mainTexture.width;
                 var h = material.mainTexture.height;
                 var sx = atlas.x*1.0f/w;
                 var sy = atlas.y * 1.0f / h;
                 var wr = atlas.width * 1.0f / w;
                 var hr = atlas.height * 1.0f / h;
                 var wr_2 = wr/2;
                 var hr_2 = hr/2;
                 material.SetFloat("_CenterX", sx + wr_2);
                 material.SetFloat("_CenterY", sy + hr_2);
                 material.SetFloat("_Width", wr_2);
                 material.SetFloat("_Height", hr_2);
                 material.SetFloat("_LengthRate",  RoundRate);
                
            }
        }
        base.OnUpdate();
    }

}

//Shader

Shader "Unlit/Transparent Colored Round"
{
    Properties
    {
        _MainTex ("Base (RGB), Alpha (A)", 2D) = "black" {}
        _CenterX("CenterX", Float) = 0.0
        _CenterY("CenterY", Float) = 0.0
        _Width("Width", Float) = 0.0
        _Height("Height", Float) = 0.0
        _LengthRate("LengthRate", Float) = 0.0
    }
    
    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;
            float _CenterX;
            float _CenterY;
            float _Width;
            float _Height;
            float _LengthRate;

            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 IN) : COLOR
            {
                float2 pt = IN.texcoord-float2(_CenterX,(1-_CenterY));
                if((pt.x*pt.x)/(_Width*_Width)+(pt.y*pt.y)/(_Height*_Height)>_LengthRate)
                {
                    discard;
                }
                
                return tex2D(_MainTex, IN.texcoord) * IN.color;
            }
            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
            }
        }
    }
}