天气系统：雨、雪

实现原理：雨和雪的实现基本类似，天空中飘的雨和雪，地上的水花和雪花，增加一个下落速度和风速，就形成了天气了。

天气雪实现步骤：

1、预生成Mesh：随机生成多个空中飘落的雪网格和地面上的雪花网格。

2、预生成雪shader和雪花shader，雪shader支持雪的显示，雪花shader支持序列帧动画显示。

3、新建一个雪相机，该相机只渲染Water层，所有和雪有关的都挂到Water层。

4、创建雪模板gameobj，模板包括MeshRenderer、雪shader创建的材质Material、MeshFilter。

5、创建雪花模板gameobj，模板包括MeshRenderer、雪花shader创建的材质Material、MeshFilter。

6、根据模板创建雪群：按高度分为上中下三层，随着时间下落到一定高度最下层会放到最上层，如此循环。

7、帧循环更新：雪相机跟随主相机偏移(xz变y不变)，雪根据下落速度变化高度，根据风速变化水平位移，风速随时间变化，雪花随时间变化显示不同的动画关键帧。

8、雪从最高点重新下落会随机更新MeshFilter中mesh网格。

9、关闭雪的时候不是一下全部消失，得有个缓冲过程，都下落到最低点的时候消失。

 

雪网格：

  1 using UnityEngine;
  2 using UnityEditor;
  3 using System.IO;
  4 using System.Collections;
  5 
  6 public class GenSnowMesh
  7 {
  8 
  9     public const int numberOfParticles = 60;   //雪的粒子数
 10     public const float areaSize = 80.0f;    //范围 因为雪的下落速度比较慢，所以范围要大一点，防止人物移动太快造成穿帮
 11     public const float areaHeight = 15.0f;  
 12     public const float particleSize = 0.3f;
 13     public const float flakeRandom = 0.1f;
 14     public const float flakeWidth = 0.15f;
 15     public static Vector3 cameraRight = new Vector3(-1, 0, 0);
 16     [MenuItem("GameEditor/scene/Weather/Snow/GenMesh")]
 17     static public void GenMesh()
 18     {
 19         for (int i = 0; i < 10; i++)
 20         {
 21             Mesh m1 = CreateMesh();
 22             AssetDatabase.CreateAsset(m1, "Assets/_Resource/model/prefab/weather/snow/SnowFx/snow_LQ" + i + ".asset");
 23         }
 24     }
 25 
 26     public static Mesh CreateMesh()
 27     {
 28         //Vector3 cameraRight1 = cameraRight * Random.Range(0.1f, 2.0f) + cameraRight * Random.Range(0.1f, 2.0f);// Vector3.forward;//Camera.main.transform.right;
 29         //cameraRight1 = Vector3.Normalize(cameraRight1);
 30         Vector3 cameraUp = new Vector3(0, 0.7f, 0.7f);
 31         Mesh mesh = new Mesh();
 32         int particleNum = numberOfParticles;
 33         Vector3[] verts = new Vector3[4 * particleNum];
 34         Vector2[] uvs = new Vector2[4 * particleNum];
 35 
 36         int[] tris = new int[2 * 3 * particleNum];
 37 
 38         Vector3 position;
 39         for (int i = 0; i < particleNum; i++)
 40         {
 41             int i4 = i * 4;
 42             int i6 = i * 6;
 43 
 44             position.x = areaSize * (Random.value - 0.5f);
 45             position.y = areaHeight * Random.value;
 46             position.z = areaSize * (Random.value - 0.5f);
 47 
 48             //float rand = Random.value;
 49             float widthWithRandom = particleSize  + Random.Range(-flakeRandom, flakeRandom);
 50             float heightWithRandom = widthWithRandom;//particleSize + rand * flakeRandom;
 51 
 52             verts[i4 + 0] = position - cameraRight * widthWithRandom;// - 0.0 * heightWithRandom;
 53             verts[i4 + 1] = position + cameraRight * widthWithRandom;// - 0.0 * heightWithRandom;
 54             verts[i4 + 2] = position + cameraRight * widthWithRandom + cameraUp * 2.0f * heightWithRandom;
 55             verts[i4 + 3] = position - cameraRight * widthWithRandom + cameraUp * 2.0f * heightWithRandom;
 56 
 57 
 58             uvs[i4 + 0] = new Vector2(0.0f, 0.0f);
 59             uvs[i4 + 1] = new Vector2(1.0f, 0.0f);
 60             uvs[i4 + 2] = new Vector2(1.0f, 1.0f);
 61             uvs[i4 + 3] = new Vector2(0.0f, 1.0f);
 62 
 63 
 64             tris[i6 + 0] = i4 + 0;
 65             tris[i6 + 1] = i4 + 1;
 66             tris[i6 + 2] = i4 + 2;
 67             tris[i6 + 3] = i4 + 0;
 68             tris[i6 + 4] = i4 + 2;
 69             tris[i6 + 5] = i4 + 3;
 70         }
 71 
 72         mesh.vertices = verts;
 73         mesh.triangles = tris;
 74         mesh.uv = uvs;
 75         mesh.RecalculateBounds();
 76 
 77         return mesh;
 78     }
 79 
 80     [MenuItem("GameEditor/scene/Weather/Snow/GenSnowLieMesh")]
 81     static public void GenSnowlieMesh()
 82     {
 83         //#if UNITY_EDITOR    
 84         //    if (generateNewAssetsOnStart) {
 85         //        // create & save 3 meshes
 86         for (int i = 0; i < 10; i++)
 87         {
 88             Mesh m1 = CreateSplashMesh();
 89             AssetDatabase.CreateAsset(m1, "Assets/_Resource/model/prefab/weather/snow/SnowFx/snowlie_LQ" + i+".asset");
 90         }
 91         //AssetDatabase.CreateAsset(m2, "Assets/Objects/RainFx/" + gameObject.name + "_LQ1.asset");
 92         //AssetDatabase.CreateAsset(m3, "Assets/Objects/RainFx/" + gameObject.name + "_LQ2.asset");
 93         //Debug.Log ("Created new rain meshes in Assets/Objects/RainFx/");
 94         //    }        
 95         //#endif
 96     }
 97 
 98     static private Mesh CreateSplashMesh()
 99     {
100         Mesh mesh = new Mesh();
101         Vector3 cameraRight1 = cameraRight * Random.Range(0.1f, 2.0f) + cameraRight * Random.Range(0.1f, 2.0f);// Vector3.forward;//Camera.main.transform.right;
102         cameraRight1 = Vector3.Normalize(cameraRight1);
103         Vector3 cameraUp = Vector3.Cross(cameraRight1, Vector3.up);
104         cameraUp = Vector3.Normalize(cameraUp);
105 
106         //int particleNum = QualityManager.quality > Quality.Medium ? numberOfParticles : numberOfParticles / 2;
107         int particleNum = numberOfParticles;
108 
109         Vector3[] verts = new Vector3[4 * particleNum];
110         Vector2[] uvs = new Vector2[4 * particleNum];
111         Vector2[] uvs2 = new Vector2[4 * particleNum];
112         Vector3[] normals = new Vector3[4 * particleNum];
113 
114         int[] tris = new int[2 * 3 * particleNum];
115 
116         Vector3 position;
117         for (int i = 0; i < particleNum; i++)
118         {
119             int i4 = i * 4;
120             int i6 = i * 6;
121 
122             position.x = areaSize * (Random.value - 0.5f);
123             position.y = 0.0f;
124             position.z = areaSize * (Random.value - 0.5f);
125 
126             float rand = Random.value;
127             float widthWithRandom = flakeWidth + Random.Range(-flakeRandom, flakeRandom);
128             float heightWithRandom = widthWithRandom;//particleSize + rand * flakeRandom;
129 
130             verts[i4 + 0] = position - cameraRight1 * widthWithRandom;// - 0.0 * heightWithRandom;
131             verts[i4 + 1] = position + cameraRight1 * widthWithRandom;// - 0.0 * heightWithRandom;
132             verts[i4 + 2] = position + cameraRight1 * widthWithRandom + cameraUp * 2.0f * heightWithRandom;
133             verts[i4 + 3] = position - cameraRight1 * widthWithRandom + cameraUp * 2.0f * heightWithRandom;
134 
135             uvs[i4 + 0] = new Vector2(0.0f, 0.0f);
136             uvs[i4 + 1] = new Vector2(1.0f, 0.0f);
137             uvs[i4 + 2] = new Vector2(1.0f, 1.0f);
138             uvs[i4 + 3] = new Vector2(0.0f, 1.0f);
139 
140             Vector2 tc1 = new Vector2(Random.Range(0.0f, 1.0f), Random.Range(0.0f, 1.0f));
141             uvs2[i4 + 0] = new Vector2(tc1.x, tc1.y);
142             uvs2[i4 + 1] = new Vector2(tc1.x, tc1.y);
143             uvs2[i4 + 2] = new Vector2(tc1.x, tc1.y);
144             uvs2[i4 + 3] = new Vector2(tc1.x, tc1.y);
145 
146             tris[i6 + 0] = i4 + 0;
147             tris[i6 + 1] = i4 + 1;
148             tris[i6 + 2] = i4 + 2;
149             tris[i6 + 3] = i4 + 0;
150             tris[i6 + 4] = i4 + 2;
151             tris[i6 + 5] = i4 + 3;
152         }
153 
154         mesh.vertices = verts;
155         mesh.triangles = tris;
156         mesh.uv = uvs;
157         mesh.uv2 = uvs2;
158         mesh.RecalculateBounds();
159         return mesh;
160     }
161 }

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