Unity实现残影特效

版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/langresser/article/details/50976029

实现效果如上图所示。代码如下：

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

// 残影效果
public class AfterImageComponent : ActorComponent
{
    class AfterImage
    {
        public Mesh mesh;
        public Material material;
        public Matrix4x4 matrix;
        public float showStartTime;
        public float duration;  // 残影镜像存在时间
        public float alpha;
        public bool needRemove = false;
    }

    private float _duration; // 残影特效持续时间
    private float _interval; // 间隔
    private float _fadeTime; // 淡出时间
    
    private List<AfterImage> _imageList = new List<AfterImage>();
    private Shader _shaderAfterImage;

    void Awake()
    {
        _shaderAfterImage = Shader.Find("Shader/AfterImage");
    }

    public void Play(float duration, float interval, float fadeout)
    {
        _duration = duration;
        _interval = interval;
        _fadeTime = fadeout;

        StartCoroutine(DoAddImage());
    }

    IEnumerator DoAddImage()
    {
        float startTime = Time.realtimeSinceStartup;
        while (true) {
            CreateImage();

            if (Time.realtimeSinceStartup - startTime > _duration) {
                break;
            }

            yield return new WaitForSeconds(_interval);
        }
    }

    private void CreateImage()
    {
        SkinnedMeshRenderer[] renderers = GetComponentsInChildren<SkinnedMeshRenderer>();
        MeshRenderer[] meshRenderers = GetComponentsInChildren<MeshRenderer>();

        CombineInstance[] combineInstances = new CombineInstance[renderers.Length + meshRenderers.Length];

        Transform t = transform;
        Material mat = null;
        for (int i = 0; i < renderers.Length; ++i) {
            var item = renderers[i];
            t = item.transform;
            mat = new Material(item.material);
            mat.shader = _shaderAfterImage;

            var mesh = new Mesh();
            item.BakeMesh(mesh);
            combineInstances[i] = new CombineInstance {
                mesh = mesh,
                subMeshIndex = 0,
            };
        }

        Mesh combinedMesh = new Mesh();
        combinedMesh.CombineMeshes(combineInstances, true, false);

        _imageList.Add(new AfterImage {
            mesh = combinedMesh,
            material = mat,
            matrix = t.localToWorldMatrix,
            showStartTime = Time.realtimeSinceStartup,
            duration = _fadeTime,
        });
    }

    private void DrawMesh(Mesh trailMesh, Material trailMaterial)
    {
        Graphics.DrawMesh(trailMesh, Matrix4x4.identity, trailMaterial, gameObject.layer);
    }

    void Update()
    {
       
    }

    void LateUpdate()
    {
        bool hasRemove = false;
        foreach (var item in _imageList) {
            float time = Time.realtimeSinceStartup - item.showStartTime;

            if (time > item.duration) {
                item.needRemove = true;
                hasRemove = true;
                continue;
            }

            if (item.material.HasProperty("_Color")) {
                item.alpha = Mathf.Max(0, 1 - time / item.duration);
                Color color = Color.white;
                color.a = item.alpha;
                item.material.SetColor("_Color", color);
            }

            Graphics.DrawMesh(item.mesh, item.matrix, item.material, gameObject.layer);
        }

        if (hasRemove) {
            _imageList.RemoveAll(x => x.needRemove);
        }
    }
}

这个并不一定是最终版本，具体效率还有待测试，多材质的关联也需要完善，不过理论上方向和思路是正确的。

核心点有：

1、创建Mesh，使用CombineInstance合并Mesh

2、使用Graphic.DrawMesh绘制模型，不需要创建额外的GameObject

3、如果要支持淡出效果，需要shader支持半透明处理