实现轮胎印

本文主要是介绍实现轮胎印，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

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.co
public class Skidmarks : MonoBehaviour {// INSPECTOR SETTINGS[SerializeField]Material skidmarksMaterial; // Material for the skidmarks to use// END INSPECTOR SETTINGSconst int MAX_MARKS = 2048; // Max number of marks total for everyone togetherconst float MARK_WIDTH = 0.35f; // Width of the skidmarks. Should match the width of the wheelsconst float GROUND_OFFSET = 0.02f;  // Distance above surface in metresconst float MIN_DISTANCE = 0.25f; // Distance between skid texture sections in metres. Bigger = better performance, less smoothconst float MIN_SQR_DISTANCE = MIN_DISTANCE * MIN_DISTANCE;// Info for each mark created. Needed to generate the correct meshclass 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 skidmarksskidmarks = 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 framemarksMesh.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 colorpublic 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 indexmarkIndex = ++markIndex % MAX_MARKS;return curIndex;}// #### PROTECTED/PRIVATE METHODS ####// Update part of the mesh for the current markIndexvoid UpdateSkidmarksMesh() {MarkSection curr = skidmarks[markIndex];// Nothing to connect to yetif (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。

因为公司原因，最终的代码不能分享。

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