刚好前几天有人问我这个问题，再加上新项目也可能用，所以这两天就研究了一下。其实如果粒子特效 和3D模型 都用RenderTexture来做的话就不会有裁切的问题，但是粒子特效用RenderTexture来做会有显示的问题，所以还是得用摄像机。废话不多说了，进入正题。

原理就是把Mask的裁切区域传给粒子特效Shader，当超出这个区域那么直接让它完全透明即可。粒子特效的源生shader大家可以去unity官网下载，我在这里把需要修改的地方标注给大家。

//add 注释中的内容就是我做修改的地方。

 

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Shader "Particles/Additive" { Properties { _TintColor ("Tint Color", Color) = (0.5,0.5,0.5,0.5) _MainTex ("Particle Texture", 2D) = "white" { } _InvFade ("Soft Particles Factor", Range(0.01,3.0)) = 1.0   //-------------------add----------------------   _MinX ("Min X", Float) = -10       _MaxX ("Max X", Float) = 10       _MinY ("Min Y", Float) = -10       _MaxY ("Max Y", Float) = 10       //-------------------add----------------------   }   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; //-------------------add---------------------- float _MinX;             float _MaxX;             float _MinY;             float _MaxY;             //-------------------add----------------------   struct appdata_t { float4 vertex : POSITION; fixed4 color : COLOR; float2 texcoord : TEXCOORD0; };   struct v2f { float4 vertex : SV_POSITION; fixed4 color : COLOR; float2 texcoord : TEXCOORD0; #ifdef SOFTPARTICLES_ON float4 projPos : TEXCOORD1; #endif //-------------------add---------------------- float3 vpos : TEXCOORD2; //-------------------add---------------------- };   float4 _MainTex_ST;   v2f vert (appdata_t v) { v2f o; //-------------------add---------------------- o.vpos = v.vertex.xyz; //-------------------add---------------------- o.vertex = mul(UNITY_MATRIX_MVP, v.vertex); #ifdef SOFTPARTICLES_ON o.projPos = ComputeScreenPos (o.vertex); COMPUTE_EYEDEPTH(o.projPos.z); #endif o.color = v.color; o.texcoord = TRANSFORM_TEX(v.texcoord,_MainTex); return o; }   sampler2D_float _CameraDepthTexture; float _InvFade;   fixed4 frag (v2f i) : SV_Target { #ifdef SOFTPARTICLES_ON float sceneZ = LinearEyeDepth (SAMPLE_DEPTH_TEXTURE_PROJ(_CameraDepthTexture, UNITY_PROJ_COORD(i.projPos))); float partZ = i.projPos.z; float fade = saturate (_InvFade * (sceneZ-partZ)); i.color.a *= fade; #endif   //-------------------add---------------------- fixed4 c =2.0f * i.color * _TintColor * tex2D(_MainTex, i.texcoord); c.a *= (i.vpos.x >= _MinX );            c.a *= (i.vpos.x <= _MaxX);              c.a *= (i.vpos.y >= _MinY);              c.a *= (i.vpos.y <= _MaxY);                  c.rgb *= c.a;                 return c;                 //-------------------add---------------------- } ENDCG } } } }

然后是自己写了个类继承Mask。把Mask的区域传给shader。

 

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using UnityEngine; using System.Collections; using UnityEngine.UI;   public class MyMask :Mask { protected override void Start () { base.Start ();   int width = Screen.width; int height = Screen.height; int designWidth = 960;//开发时分辨率宽 int designHeight = 640;//开发时分辨率高 float s1 = (float)designWidth / (float)designHeight; float s2 = (float)width / (float)height;   //目标分辨率小于 960X640的 需要计算缩放比例 float contentScale =1f; if(s1 > s2) { contentScale = s1/s2; } Canvas canvas = GameObject.Find("Canvas").GetComponent<Canvas>(); Vector2 pos; if(RectTransformUtility.ScreenPointToLocalPointInRectangle(canvas.transform as RectTransform, transform.position, canvas.camera, out pos)){ ParticleSystem  [] particlesSystems = transform.GetComponentsInChildren<ParticleSystem>(); RectTransform rectTransform = transform as RectTransform; float minX,minY,maxX,maxY; minX = rectTransform.rect.x  + pos.x; minY = rectTransform.rect.y+ pos.y; maxX = minX + rectTransform.rect.width ; maxY = minY + rectTransform.rect.height;     //这里 100  是因为ugui默认的缩放比例是100  你也可以去改这个值，但是我觉得最好别改。 foreach(ParticleSystem particleSystem in particlesSystems) { particleSystem.renderer.sharedMaterial.SetFloat("_MinX",minX/100/contentScale); particleSystem.renderer.sharedMaterial.SetFloat("_MinY",minY/100/contentScale); particleSystem.renderer.sharedMaterial.SetFloat("_MaxX",maxX/100/contentScale); particleSystem.renderer.sharedMaterial.SetFloat("_MaxY",maxY/100/contentScale); } } } }

OK，如下图所示，把粒子特效直接挂在Mask下面， 就可以进行裁切了。。