UGUI ScrollView中显示模型和特效

游戏开发中有时候会遇到在UI上显示模型和特效的需求，这次需要在ScrollView上显示。我们使用UGUI的Screen Space - Camera模式，修改模型和特效的layer使之显示在UI上面，但是会遇到ScrollView的mask无法剔除模型和特效的问题。

解决思路：计算出ScrollView的显示矩形框的世界坐标和尺寸，传给模型和特效的shader，在shader里判断这个像素的世界坐标是否超过矩形框，来判断是否显示图像。

C#代码部分：

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class ScrollViewModelAndEffectClip : MonoBehaviour
{

    public  RectTransform scrollViewArea;
    float mWidth, mHeight, m_canvasScale;
    Canvas mCanvas;
    public  Vector4 area;
    List<Material> modelMaterials = new List<Material>();
    // Start is called before the first frame update
    void Start()
    {

        var renderers=GetComponentsInChildren<Renderer>();
        for(int i = ; i < renderers.Length; i++)
        {
            //Debug.LogError(renderers[i]);
            modelMaterials.AddRange(renderers[i].GetMaterials());
        }
        for(int i = ; i < modelMaterials.Count; i++)
        {
            modelMaterials[i].shader = Shader.Find(modelMaterials[i].shader.name + "ScrollViewClip");
            //Debug.LogError(modelMaterials[i].shader.name + "ScrollViewClip");
        }

        mCanvas = GetComponentInParent<Canvas>();
        GetArea();
    }

    // Update is called once per frame
    void Update()
    {

    }

    public void GetArea()
    {
        m_canvasScale = mCanvas.transform.localScale.x;
        mWidth = scrollViewArea.rect.width * m_canvasScale;
        mHeight = scrollViewArea.rect.height * m_canvasScale;

        area = CalculateArea(scrollViewArea.position, scrollViewArea.pivot);

        for (int i = ; i < modelMaterials.Count; i++)
        {
            //Debug.LogError(area);
            modelMaterials[i].SetVector("_Area", area);
        }

    }

    Vector4 CalculateArea(Vector3 position,Vector2 pivot)
    {
        return new Vector4()
        {
            x = position.x - mWidth*pivot.x,
            y = position.y - mHeight * pivot.y,
            z = position.x + mWidth *(- pivot.x),
            w = position.y + mHeight * ( - pivot.y)
        };
    }

}

接下来是Shader：

Shader "SonicDance/AddtiveScrollViewClip"
{
    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
            //Clip新增
        _Area("Area", Vector) = (,,,)
            //
    }

    Category
    {
        SubShader
        {
            Tags { "Queue"="Transparent" "IgnoreProjector"="True" "RenderType"="Transparent" "PreviewType"="Plane" }
            Blend SrcAlpha OneMinusSrcAlpha
            ColorMask RGB
            Cull Off
            Lighting Off
            ZWrite Off

            Pass {

                CGPROGRAM
                #pragma vertex vert
                #pragma fragment frag
                #pragma target 2.0
                #pragma multi_compile_particles
                #pragma multi_compile_fog

                #include "UnityCG.cginc"

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

                };

                struct v2f
                {
                    float4 vertex : SV_POSITION;
                    fixed4 color : COLOR;
                    float4 texcoord : TEXCOORD0;
                    float4 worldPos:TEXCOORD3;
                    UNITY_FOG_COORDS()
                    #ifdef SOFTPARTICLES_ON
                    float4 projPos : TEXCOORD2;
                    #endif
                    UNITY_VERTEX_OUTPUT_STEREO

                };

                uniform sampler2D _MainTex;
                uniform fixed4 _TintColor;
                uniform float4 _MainTex_ST;
                uniform sampler2D_float _CameraDepthTexture;
                uniform float _InvFade;
                //Clip新增
                float4 _Area;
                //

                v2f vert ( appdata_t v  )
                {
                    v2f o;
                    UNITY_SETUP_INSTANCE_ID(v);
                    UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(o);

                    v.vertex.xyz +=  float3( , ,  ) ;
                    o.vertex = UnityObjectToClipPos(v.vertex);
                    o.worldPos= mul(unity_ObjectToWorld, v.vertex);
                    #ifdef SOFTPARTICLES_ON
                        o.projPos = ComputeScreenPos (o.vertex);
                        COMPUTE_EYEDEPTH(o.projPos.z);
                    #endif
                    o.color = v.color;
                    o.texcoord = v.texcoord;
                    UNITY_TRANSFER_FOG(o,o.vertex);
                    return o;
                }

                fixed4 frag ( v2f i  ) : SV_Target
                {

                    //新增，判断顶点坐标是否在裁剪框内

                    bool inArea = i.worldPos.x >= _Area.x && i.worldPos.x <= _Area.z && i.worldPos.y >= _Area.y && i.worldPos.y <= _Area.w;
                    if (!inArea)
                        discard;
                    //----end----

                    #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

                    fixed4 col = 2.0f * i.color * _TintColor * tex2D(_MainTex, i.texcoord.xy*_MainTex_ST.xy + _MainTex_ST.zw );
                    UNITY_APPLY_FOG(i.fogCoord, col);
                    return col;
                }
                ENDCG
            }
        }
    }
    CustomEditor "ASEMaterialInspector"
}

这个方法有一个问题就是，需要复制一份显示的模型和特效的shader，并且增加上面shader中注释的部分，如果模型和特效的shader多种多样的话，那工作量就比较大，需要其他的方法。