Unity NGUI UIPanel下对粒子或自定义Mesh的剪裁

写在开篇：
越来越烦那些无脑转发自己不做验证的博主论坛楼主，网上好不容易找到一些资料，结果代码搞下来却是错的，有些确实是因为版本问题太老不兼容，但是有些明显是有问题的，转发前自己试试就知道肯定是不能用的。结果。。。哎。。。真是不想说啥了。
这次是在小地图中画线画圈，用到了动态绘制Mesh，小地图需要对这些线进行裁切，所以去网上搜了一篇叫做《Unity NGUI UIPanel下对粒子的剪裁》的文章。当然还是感谢一下原作者提供的思路。我这里对这篇文章中涉及到的代码进行了优化改动，使之可以使用。没错！使之可以使用！！！不然没法用啊啊啊啊！！！还有让我最抓狂的一点，就是某些特定分辨率下裁切范围有问题的bug，我也改掉了！！！
废话不多说了，上代码
CustomUIClipper.cs

using System;
using UnityEngine;

[RequireComponent(typeof(UIPanel))]
public class CustomUIClipper : MonoBehaviour
{
const string ShaderName = "Bleach/Particles Additive Area Clip";
const float ClipInterval = 0.5f;

UIPanel m_targetPanel;
Shader m_shader;

void Start()
{
// find panel
m_targetPanel = GetComponent<UIPanel>();

if (m_targetPanel == null)
throw new ArgumentNullException("Cann't find the right UIPanel");
if (m_targetPanel.clipping != UIDrawCall.Clipping.SoftClip)
throw new InvalidOperationException("Don't need to clip");

m_shader = Shader.Find(ShaderName);

//if (!IsInvoking("Clip"))
//    InvokeRepeating("Clip", 0, ClipInterval);

Clip();
}

Vector4 CalcClipArea()
{
var clipRegion = m_targetPanel.finalClipRegion;
Vector4 nguiArea = new Vector4()
{
x = clipRegion.x - clipRegion.z / 2,
y = clipRegion.y - clipRegion.w / 2,
z = clipRegion.x + clipRegion.z / 2,
w = clipRegion.y + clipRegion.w / 2
};

var uiRoot = m_targetPanel.root;
var pos = m_targetPanel.transform.position;
float rate1 = (float)Screen.width / (float)Screen.height;
float rate2 = (float)uiRoot.manualWidth / (float)uiRoot.manualHeight;
float h = 2f;
float w = h * rate1;
float tempH = h / uiRoot.manualHeight;
float tempW = w / uiRoot.manualWidth;
float tempRate = Mathf.Max(tempW, tempH);
if (rate1 < rate2)
{
tempRate = Mathf.Min(tempW, tempH);
}

Vector4 result =  new Vector4()
{
x = pos.x + nguiArea.x * tempRate,
y = pos.y + nguiArea.y * tempRate,
z = pos.x + nguiArea.z * tempRate,
w = pos.y + nguiArea.w * tempRate
};

return result;
}

void Clip()
{
Vector4 clipArea = CalcClipArea();
Renderer[] renderers = GetComponentsInChildren<Renderer>();
for (int i = 0; i < renderers.Length; ++i)
{
var mat = renderers[i].material;

if (mat.shader.name != ShaderName)
mat.shader = m_shader;

mat.SetVector("_Area", clipArea);
}
}

void OnDestroy()
{
//CancelInvoke("Clip");
}
}

将这个文件挂载到带有裁切功能的UIPanel上
这个Panel下的粒子或者Mesh使用的shader代码如下：

Shader "Bleach/Particles Additive Area Clip"
{
Properties
{
_TintColor ("Tint Color", Color) = (0.5,0.5,0.5,0.5)
_MainTex ("Particle Texture", 2D) = "white" {}
_Area ("Area", Vector) = (0,0,1,1)
}

Category
{
Tags { "Queue"="Transparent" "IgnoreProjector"="True" "RenderType"="Transparent" }
Blend SrcAlpha One
AlphaTest Greater .01
ColorMask RGB
Cull Off
Lighting Off
ZWrite Off
Fog { Color (0,0,0,0) }

SubShader
{
Pass
{
CGPROGRAM
#pragma vertex vert
#pragma fragment frag
#pragma multi_compile_particles

#include "UnityCG.cginc"

sampler2D _MainTex;
fixed4 _TintColor;
float4 _Area;

struct appdata_t
{
float4 vertex : POSITION;
fixed4 color : COLOR;
float2 texcoord : TEXCOORD0;
};

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

float4 _MainTex_ST;

v2f vert (appdata_t v)
{
v2f o;
o.vertex = mul(UNITY_MATRIX_MVP, v.vertex);
o.texcoord = TRANSFORM_TEX(v.texcoord,_MainTex);
o.color = v.color;
o.worldPos = mul(_Object2World, v.vertex).xy;
return o;
}

fixed4 frag (v2f i) : SV_Target
{
bool inArea = i.worldPos.x >= _Area.x && i.worldPos.x <= _Area.z && i.worldPos.y >= _Area.y && i.worldPos.y <= _Area.w;
return inArea? 2.0f * i.color * _TintColor * tex2D(_MainTex, i.texcoord) : fixed4(0,0,0,0);
}
ENDCG
}
}
}
}

如果有需要对shader做改动的，就用这个为范本进行修改吧
大功告成

哦对了，我这里进行了优化，如果Panel尺寸不变并且子对象不会动态添加，可以不用进行重复发送裁切数据，请大家根据自己的情况进行代码修改，如果有以上的情况，将Clip函数的Invoke调用注释打开即可