实现轮胎印

接到一个任务，实现一个轮胎印记。特效用粒子做的效果， 感觉不是很好。主程大哥说，那程序来实现吧。

关键词

• 主程大哥，给了一些关键词。
• TrailRender
• Decal

• 在项目使用的版本上,纹理贴图是被拉伸的，实际是要的纹理复制使用，看网格的效果如下，在SomeTips的skidmarksTest.sence
  
  

• 看到Unity5.6.2.f上，使用TrailRender可以实现想要的效果,demo 的SkidmarksTest.unity
  
  

网格控制-网络

• 看到一个解决方案，是网格动画，参考A skidmark effect for vehicles in Unity3D
• 从文章的中github看到案例。是在初始化一定数目的网格，然后根据位置来使用。
• 代码分析

using UnityEngine;using UnityEngine.Rendering;// Skidmarks controller. Put one of these in a scene somewhere. Call AddSkidMark.// Copyright 2017 Nition, BSD licence (see LICENCE file). http://nition.copublic class Skidmarks : MonoBehaviour {    // INSPECTOR SETTINGS    [SerializeField]    Material skidmarksMaterial; // Material for the skidmarks to use    // END INSPECTOR SETTINGS    const int MAX_MARKS = 2048; // Max number of marks total for everyone together    const float MARK_WIDTH = 0.35f; // Width of the skidmarks. Should match the width of the wheels    const float GROUND_OFFSET = 0.02f;  // Distance above surface in metres    const float MIN_DISTANCE = 0.25f; // Distance between skid texture sections in metres. Bigger = better performance, less smooth    const float MIN_SQR_DISTANCE = MIN_DISTANCE * MIN_DISTANCE;    // Info for each mark created. Needed to generate the correct mesh    class MarkSection {        public Vector3 Pos = Vector3.zero;        public Vector3 Normal = Vector3.zero;        public Vector4 Tangent = Vector4.zero;        public Vector3 Posl = Vector3.zero;        public Vector3 Posr = Vector3.zero;        public byte Intensity;        public int LastIndex;    };    int markIndex;    MarkSection[] skidmarks;    Mesh marksMesh;    MeshRenderer mr;    MeshFilter mf;    Vector3[] vertices;    Vector3[] normals;    Vector4[] tangents;    Color32[] colors;    Vector2[] uvs;    int[] triangles;    bool meshUpdated;    bool haveSetBounds;    // #### UNITY INTERNAL METHODS ####    protected void Start() {        // Generate a fixed array of skidmarks        skidmarks = new MarkSection[MAX_MARKS];        for (int i = 0; i < MAX_MARKS; i++) {            skidmarks[i] = new MarkSection();        }        mf = GetComponent<MeshFilter>();        mr = GetComponent<MeshRenderer>();        if (mr == null) {            mr = gameObject.AddComponent<MeshRenderer>();        }        marksMesh = new Mesh();        marksMesh.MarkDynamic();        if (mf == null) {            mf = gameObject.AddComponent<MeshFilter>();        }        mf.sharedMesh = marksMesh;        vertices = new Vector3[MAX_MARKS * 4];        normals = new Vector3[MAX_MARKS * 4];        tangents = new Vector4[MAX_MARKS * 4];        colors = new Color32[MAX_MARKS * 4];        uvs = new Vector2[MAX_MARKS * 4];        triangles = new int[MAX_MARKS * 6];        mr.shadowCastingMode = ShadowCastingMode.Off;        mr.receiveShadows = false;        mr.material = skidmarksMaterial;        mr.lightProbeUsage = LightProbeUsage.Off;    }    protected void LateUpdate() {        if (!meshUpdated) return;        meshUpdated = false;        // Reassign the mesh if it's changed this frame        marksMesh.vertices = vertices;        marksMesh.normals = normals;        marksMesh.tangents = tangents;        marksMesh.triangles = triangles;        marksMesh.colors32 = colors;        marksMesh.uv = uvs;        if (!haveSetBounds) {            // Could use RecalculateBounds here each frame instead, but it uses about 0.1-0.2ms each time            // Save time by just making the mesh bounds huge, so the skidmarks will always draw            // Not sure why I only need to do this once, yet can't do it in Start (it resets to zero)            marksMesh.bounds = new Bounds(new Vector3(0, 0, 0), new Vector3(10000, 10000, 10000));            haveSetBounds = true;        }        mf.sharedMesh = marksMesh;    }    // #### PUBLIC METHODS ####    // Function called by the wheel that's skidding. Sets the intensity of the skidmark section    // by setting the alpha of the vertex color    public int AddSkidMark(Vector3 pos, Vector3 normal, float intensity, int lastIndex) {        if (intensity > 1) intensity = 1.0f;        else if (intensity < 0) return -1;        if (lastIndex > 0) {            float sqrDistance = (pos - skidmarks[lastIndex].Pos).sqrMagnitude;            if (sqrDistance < MIN_SQR_DISTANCE) return lastIndex;        }        MarkSection curSection = skidmarks[markIndex];        curSection.Pos = pos + normal * GROUND_OFFSET;        curSection.Normal = normal;        curSection.Intensity = (byte)(intensity * 255f);        curSection.LastIndex = lastIndex;        if (lastIndex != -1) {            MarkSection lastSection = skidmarks[lastIndex];            Vector3 dir = (curSection.Pos - lastSection.Pos);            Vector3 xDir = Vector3.Cross(dir, normal).normalized;            curSection.Posl = curSection.Pos + xDir * MARK_WIDTH * 0.5f;            curSection.Posr = curSection.Pos - xDir * MARK_WIDTH * 0.5f;            curSection.Tangent = new Vector4(xDir.x, xDir.y, xDir.z, 1);            if (lastSection.LastIndex == -1) {                lastSection.Tangent = curSection.Tangent;                lastSection.Posl = curSection.Pos + xDir * MARK_WIDTH * 0.5f;                lastSection.Posr = curSection.Pos - xDir * MARK_WIDTH * 0.5f;            }        }        UpdateSkidmarksMesh();        int curIndex = markIndex;        // Update circular index        markIndex = ++markIndex % MAX_MARKS;        return curIndex;    }    // #### PROTECTED/PRIVATE METHODS ####    // Update part of the mesh for the current markIndex    void UpdateSkidmarksMesh() {        MarkSection curr = skidmarks[markIndex];        // Nothing to connect to yet        if (curr.LastIndex == -1) return;        MarkSection last = skidmarks[curr.LastIndex];        vertices[markIndex * 4 + 0] = last.Posl;        vertices[markIndex * 4 + 1] = last.Posr;        vertices[markIndex * 4 + 2] = curr.Posl;        vertices[markIndex * 4 + 3] = curr.Posr;        normals[markIndex * 4 + 0] = last.Normal;        normals[markIndex * 4 + 1] = last.Normal;        normals[markIndex * 4 + 2] = curr.Normal;        normals[markIndex * 4 + 3] = curr.Normal;        tangents[markIndex * 4 + 0] = last.Tangent;        tangents[markIndex * 4 + 1] = last.Tangent;        tangents[markIndex * 4 + 2] = curr.Tangent;        tangents[markIndex * 4 + 3] = curr.Tangent;        colors[markIndex * 4 + 0] = new Color32(0, 0, 0, last.Intensity);        colors[markIndex * 4 + 1] = new Color32(0, 0, 0, last.Intensity);        colors[markIndex * 4 + 2] = new Color32(0, 0, 0, curr.Intensity);        colors[markIndex * 4 + 3] = new Color32(0, 0, 0, curr.Intensity);        uvs[markIndex * 4 + 0] = new Vector2(0, 0);        uvs[markIndex * 4 + 1] = new Vector2(1, 0);        uvs[markIndex * 4 + 2] = new Vector2(0, 1);        uvs[markIndex * 4 + 3] = new Vector2(1, 1);        triangles[markIndex * 6 + 0] = markIndex * 4 + 0;        triangles[markIndex * 6 + 2] = markIndex * 4 + 1;        triangles[markIndex * 6 + 1] = markIndex * 4 + 2;        triangles[markIndex * 6 + 3] = markIndex * 4 + 2;        triangles[markIndex * 6 + 5] = markIndex * 4 + 1;        triangles[markIndex * 6 + 4] = markIndex * 4 + 3;        meshUpdated = true;    }}

• 在LateUpdate()对位置做处理。
• 在理解了demo中用使用WheelCollider，rigidbody。其实是针对速度有每帧计算，速度大于0.5f有了颜色深浅的变化。还有在Y方向上，给予了(0,1,0)* 0.02f偏移值，和地面有一点间距。
• 针对项目中具体使用，加速度部分是可以不用的，但是从效率的角度考虑，mesh的数量不要太多，可以复用。同时可以随着时间渐渐隐藏。
• 不断使用回收，像对象池一样的。在原来的基础上，对代码做了二次开发。
• 在渲染角度上，只增加了一个DrawCall。
• 网络长度上和渐隐时间可以在预制件上修改，让美术调整出最好的效果。
• 当然发现自己计算的把运动物体本身的位移忽视了。

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因为公司原因，最终的代码不能分享。