1 需求描述

        本文将模拟激光灯（或碰撞）特效，详细需求如下：

• 从鼠标位置发射屏幕射线，检测是否与物体发生碰撞
• 当与物体发生碰撞时，在物体表面覆盖一层激光灯（或碰撞）特效

        本文代码见→激光灯、碰撞特效

2 原理

        获取屏幕射线与物体的碰撞点，并在 shader 中计算顶点与碰撞点的距离（记为 dist），通过以下衰减函数计算顶点对应的透明度，透明度随碰撞点的距离增大逐渐减小，激光灯（或碰撞）效果逐渐减弱。

alpha = pow(exp(-dist), 4)

        为使特效更加逼真，激光灯（或碰撞）特效的红色分量由以下漫反射公式控制。其中，red 为红色分量值，λ 为漫反射因子，值越大，漫反射效果越强，本文 λ = 0.1；lightDir 为顶点光源向量，normalDir 为顶点法线向量。

red = λ * dot(lightDir, normalDir) + (1 - λ)

3 需求实现

        SelectController.cs

using UnityEngine;
 
public class SelectController : MonoBehaviour { // 单击选中控制
    private Transform target; // 选中的目标
    private RaycastHit hit; // 碰撞信息
 
    private void Update() {
        if (Input.GetMouseButtonUp(0)) {
            Transform temp = GetHitTrans();
            if (temp != target) {
                DrawEffect(target, temp);
                target = temp;
            }
        }
    }

    private void DrawEffect(Transform old, Transform now) { // 绘制特效
        DrawEffect(old, false);
        DrawEffect(now, true);
    }

    private void DrawEffect(Transform trans, bool enable) { // 绘制特效
        if (trans != null) {
            foreach(Transform child in trans.transform.GetComponents<Transform>()) {
                if (child.GetComponent<ColliderEffect>() == null) {
                    if (enable) {
                        child.gameObject.AddComponent<ColliderEffect>();
                    }
                }
                else {
                    child.GetComponent<ColliderEffect>().enabled = enable;
                }
            }
        }
    }
 
    private Transform GetHitTrans() { // 获取屏幕射线碰撞的物体
        Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
        if (Physics.Raycast(ray, out hit)) {
            return hit.transform;
        }
        return null;
    }
}

        ColliderEffect.cs

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

[DisallowMultipleComponent]
public class ColliderEffect : MonoBehaviour { // 激光灯(或碰撞)特效
    private Renderer[] renderers; // 当前对象及其子对象的渲染器
    private Material colliderMaterial; // 激光灯(碰撞)材质
    private Vector4 hitPos; // 碰撞点
    private RaycastHit hit; // 碰撞信息

    private void Awake() {
        renderers = GetComponentsInChildren<Renderer>();
        colliderMaterial = new Material(Shader.Find("MyShader/ColliderEffect"));
        hitPos = Vector4.zero;
        CombineSubmeshes();
    }

    private void OnEnable() {
        hitPos = GetHitPoint();
        colliderMaterial.SetVector("_HitPos", hitPos);
        foreach (var renderer in renderers) {
            List<Material> materials = renderer.sharedMaterials.ToList();
            materials.Add(colliderMaterial);
            renderer.sharedMaterials = materials.ToArray();
        }
    }

    private void Update() {
        hitPos = GetHitPoint();
        if (!hitPos.Equals(Vector4.zero)) {
            colliderMaterial.SetInt("_Enable", 1);
            colliderMaterial.SetVector("_HitPos", hitPos);
        } else {
            colliderMaterial.SetInt("_Enable", 0);
        }
    }

    private void OnDisable() {
        foreach (var renderer in renderers) {
            List<Material> materials = renderer.sharedMaterials.ToList();
            materials.Remove(colliderMaterial);
            renderer.sharedMaterials = materials.ToArray();
        }
    }

    private Vector4 GetHitPoint() {
        Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
        if (Physics.Raycast(ray, out hit, 1000) && hit.transform == transform) {
            return hit.point;
        }
        return Vector4.zero;
    }

    private void CombineSubmeshes() { // 绑定子网格
        foreach (var meshFilter in GetComponentsInChildren<MeshFilter>()) {
            var renderer = meshFilter.GetComponent<Renderer>();
            if (renderer != null) {
                CombineSubmeshes(meshFilter.sharedMesh, renderer.sharedMaterials.Length);
            }
        }
        foreach (var skinnedMeshRenderer in GetComponentsInChildren<SkinnedMeshRenderer>()) {
            CombineSubmeshes(skinnedMeshRenderer.sharedMesh, skinnedMeshRenderer.sharedMaterials.Length);
        }
    }

    private void CombineSubmeshes(Mesh mesh, int materialsLength) { // 绑定子网格
        if (mesh.subMeshCount == 1) {
            return;
        }
        if (mesh.subMeshCount > materialsLength) {
            return;
        }
        mesh.subMeshCount++;
        mesh.SetTriangles(mesh.triangles, mesh.subMeshCount - 1);
    }
}

        ColliderEffect.shader

Shader "MyShader/ColliderEffect" {
    Properties {
        _HitPos ("HitPos", Vector) = (0, 0, 0, 0) // 屏幕射线碰撞位置
        _Enable ("Enable", Int) = 0 // 是否开启特效
    }

    SubShader {
        Tags {
            // 渲染队列: Background(1000, 后台)、Geometry(2000, 几何体, 默认)、Transparent(3000, 透明)、Overlay(4000, 覆盖)
            "Queue" = "Transparent+110"
            "RenderType" = "Transparent"
            "DisableBatching" = "True"
        }

        Pass {
            Blend SrcAlpha OneMinusSrcAlpha // 混合测试, 与背后的物体颜色混合

            CGPROGRAM
            #include "UnityCG.cginc"

            #pragma vertex vert
            #pragma fragment frag

            uniform int _Enable;
            uniform float4 _HitPos;
   
            struct appdata {
                float4 vertex : POSITION;
                float3 normal : NORMAL;
            };

            struct v2f {
                float4 worldPos : TEXCOORD0;
                float3 worldNormal : Normal;
                float4 clipPos : SV_POSITION;
            };

            v2f vert(appdata input) {
                v2f output;
                output.worldPos = mul(unity_ObjectToWorld, input.vertex); // 世界坐标系下顶点坐标
                output.worldNormal = UnityObjectToWorldNormal(input.normal); // 世界坐标系下顶点法线向量
                output.clipPos = UnityObjectToClipPos(input.vertex); // 裁剪坐标系下顶点坐标
                return output;
            }

            fixed4 frag(v2f input) : SV_Target {
                if(_Enable == 1)
				{
                    float3 worldLightDir = normalize(UnityWorldSpaceLightDir(input.worldPos)); // 世界坐标系下由顶点指向光源的方向向量
                    float diffuse = (0.1 * dot(worldLightDir, input.worldNormal.xyz) + 0.9); // 漫反射颜色强度
                    float dist = distance(input.worldPos.xyz, _HitPos);
                    float alpha = pow(exp(-dist), 4); // 透明度(随距离衰减)
                    return float4(diffuse , 0, 0, alpha);
				}
				else
				{
					return float4(0, 0, 0, 0);
				}
            }

            ENDCG
        }
    }
}

4 运行效果

5 推荐阅读

•  渲染管线
• 固定管线着色器一
• 固定管线着色器二
• 表面着色器
• 顶点和片元着色器
• 选中物体描边特效
• 基于模板测试和顶点膨胀的描边方法
• 水波特效
• 半球卷屏特效
• 卷轴特效