寫在開篇：

越來越煩那些無腦轉發自己不做驗證的博主論壇樓主，網上好不容易找到一些資料，結果代碼搞下來卻是錯的，有些確實是因為版本問題太老不兼容，但是有些明顯是有問題的，轉發前自己試試就知道肯定是不能用的。結果。。。哎。。。真是不想說啥了。

這次是在小地圖中畫線畫圈，用到了動態繪制Mesh，小地圖需要對這些線進行裁切，所以去網上搜了一篇叫做《Unity NGUI UIPanel下對粒子的剪裁》的文章。當然還是感謝一下原作者提供的思路。我這裏對這篇文章中涉及到的代碼進行了優化改動，使之可以使用。沒錯！使之可以使用！！！不然沒法用啊啊啊啊！！！還有讓我最抓狂的一點，就是某些特定分辨率下裁切範圍有問題的bug，我也改掉了！！！

廢話不多說了，上代碼

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");
    }
}

將這個文件掛載到帶有裁切功能的UIPanel上

這個Panel下的粒子或者Mesh使用的shader代碼如下：

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 
            }
        }    
    }
}

如果有需要對shader做改動的，就用這個為範本進行修改吧

大功告成

哦對了，我這裏進行了優化，如果Panel尺寸不變並且子對象不會動態添加，可以不用進行重復發送裁切數據，請大家根據自己的情況進行代碼修改，如果有以上的情況，將Clip函數的Invoke調用註釋打開即可

本文出自 “月之影·影之海” 博客，請務必保留此出處http://abyss.blog.51cto.com/3625755/1982795

Unity NGUI UIPanel下對粒子或自定義Mesh的剪裁