Mesh网格编程(一） 流体

Mesh网格编程（一） 流体水

通过Mesh网格随Sin函数实时变化模拟液体的流动，从而达到动态水的效果。

效果图：

Mesh网格编程步骤:

一：确定数量

确定该几何图形应有多少个三角形面，顶点坐标、顶点序列、UV贴图、法线向量皆为三角形面数的三倍。

二：根据三角形面确定顶点坐标

这里我习惯把一个面的顶点确定好之后再去找下一个面，这样做可以是法线和顶点序列确定起来很容易。但是要注意的是在确定顶点时要按照顺时针顺序确定，否则会导致三角形面相反。

三：确定法线

法线大致分为两种：
其一是棱角分明的几何体，这种几何体的法线可以用确定好的顶点坐标两两相减，得到的向量做叉乘并赋值给三个顶点上的法线。
其二是圆滑的几何体，这种几何体需要求出该点在曲面上的切线，从而确定垂直于切线的法线。如果是圆形。可以使用顶点减圆心所得的向量。
此外，求得的法线尽量单位化，否则可能出现一个面上的颜色不同。

四：确定顶点序列

若三角形顶点按照面数去确定，顶点序列就会变得非常简单，按顺序赋值即可。

五：确定UV贴图

根据所做几何体的不同，贴图左边也会有所改变，并不固定。

六：创建网格

实现代码如下：

using UnityEngine;
using System.Collections;

public class Water : MonoBehaviour {

	Mesh mesh;

	public int tier = 10;			//长度分段
	private float length = 10;		//长
	private int width = 3;			//宽
	private int hight = 10;			//高

	private Vector3[] vs;			//顶点坐标
	private int[] ts;				//顶点序列
	private Vector2[] newUVs;		//UV贴图
	private Vector3[] newNormals;	//法线
	
	void Update () {

		int temp = ((tier + 1) * 8 + 4) * 3;	//确定顶点数量

		vs = new Vector3[temp];
		ts = new int[temp];
		newUVs = new Vector2[temp];
		newNormals = new Vector3[temp];

		float dis = 2 * Mathf.PI / tier;		//两段之差的横坐标

		int count = 0;
		for (int i = 0; i < tier; i++) {

			float pos1 = i * length / tier - length / 2;
			float pos2 = (i + 1) * length / tier - length / 2;
			//顶面顶点坐标
			vs[count] = new Vector3(pos1,Mathf.Sin(Time.time + i * dis), width);
			vs[count + 1] = new Vector3(pos2,Mathf.Sin(Time.time + (i + 1) * dis), -width);
			vs[count + 2] = new Vector3(pos1,Mathf.Sin(Time.time + i * dis), -width);

			vs[count + 3] = new Vector3(pos1,Mathf.Sin(Time.time + i * dis), width);
			vs[count + 4] = new Vector3(pos2,Mathf.Sin(Time.time + (i + 1) * dis), width);
			vs[count + 5] = new Vector3(pos2,Mathf.Sin(Time.time + (i + 1) * dis), -width);
			//顶面法线
			newNormals[count] = Vector3.Normalize(new Vector3(1,Mathf.Cos(Time.time + i * dis), 0));
			newNormals[count + 1] = Vector3.Normalize(new Vector3(1,Mathf.Cos(Time.time + (i + 1) * dis), 0));
			newNormals[count + 2] = Vector3.Normalize(new Vector3(1,Mathf.Cos(Time.time + i * dis), 0));
				
			newNormals[count + 3] = Vector3.Normalize(new Vector3(1,Mathf.Cos(Time.time + i * dis), 0));
			newNormals[count + 4] = Vector3.Normalize(new Vector3(1,Mathf.Cos(Time.time + (i + 1) * dis), 0));
			newNormals[count + 5] = Vector3.Normalize(new Vector3(1,Mathf.Cos(Time.time + (i + 1) * dis), 0));

			//前面顶点坐标
			vs[count + 6] = new Vector3(pos1,Mathf.Sin(Time.time + i * dis), -width);
			vs[count + 7] = new Vector3(pos2,-hight, -width);
			vs[count + 8] = new Vector3(pos1,-hight, -width);

			vs[count + 9] = new Vector3(pos1,Mathf.Sin(Time.time + i * dis), -width);
			vs[count + 10] = new Vector3(pos2,Mathf.Sin(Time.time + (i + 1) * dis), -width);
			vs[count + 11] = new Vector3(pos2,-hight, -width);
			//前面法线
			for (int j = 0; j < 6; j++) {
				newNormals[count + 6 + j] = Vector3.back;
			}
			//后面顶点坐标
			vs[count + 12] = new Vector3(pos1,Mathf.Sin(Time.time + i * dis), width);
			vs[count + 13] = new Vector3(pos1,-hight, width);
			vs[count + 14] = new Vector3(pos2,-hight, width);
			
			vs[count + 15] = new Vector3(pos1,Mathf.Sin(Time.time + i * dis), width);
			vs[count + 16] = new Vector3(pos2,-hight, width);
			vs[count + 17] = new Vector3(pos2,Mathf.Sin(Time.time + (i + 1) * dis), width);
			//后面法线
			for (int j = 0; j < 6; j++) {
				newNormals[count + 12 + j] = Vector3.forward;
			}
			//下面顶点坐标
			vs[count + 18] = new Vector3(pos1,-hight, width);
			vs[count + 19] = new Vector3(pos1,-hight, -width);
			vs[count + 20] = new Vector3(pos2,-hight, -width);

			vs[count + 21] = new Vector3(pos1,-hight, width);
			vs[count + 22] = new Vector3(pos2,-hight, -width);
			vs[count + 23] = new Vector3(pos2,-hight, width);
			//下面法线
			for (int j = 0; j < 6; j++) {
				newNormals[count + 18 + j] = Vector3.down;
			}

			count += 24;
		}

		//两侧顶点坐标及法线
		vs [vs.Length - 12] = new Vector3 (-length / 2, Mathf.Sin (Time.time), width);
		vs [vs.Length - 11] = new Vector3 (-length / 2, -hight, -width);
		vs [vs.Length - 10] = new Vector3 (-length / 2, -hight, width);

		vs [vs.Length - 9] = new Vector3 (-length / 2, Mathf.Sin (Time.time), width);
		vs [vs.Length - 8] = new Vector3 (-length / 2, Mathf.Sin (Time.time), -width);
		vs [vs.Length - 7] = new Vector3 (-length / 2, -hight, -width);

		for (int j = 0; j < 6; j++) {
			newNormals[vs.Length - 12 + j] = Vector3.left;
		}

		vs [vs.Length - 6] = new Vector3 (length / 2, Mathf.Sin (Time.time + tier * dis), width);
		vs [vs.Length - 5] = new Vector3 (length / 2, -hight, width);
		vs [vs.Length - 4] = new Vector3 (length / 2, -hight, -width);

		vs [vs.Length - 3] = new Vector3 (length / 2, Mathf.Sin (Time.time + tier * dis), width);
		vs [vs.Length - 2] = new Vector3 (length / 2, -hight, -width);
		vs [vs.Length - 1] = new Vector3 (length / 2, Mathf.Sin (Time.time + tier * dis), -width);

		for (int j = 0; j < 6; j++) {
			newNormals[vs.Length - 6 + j] = Vector3.right;
		}

		for (int i = 0; i < ts.Length; i++) {	//顶点序列赋值
			ts[i] = i;
		}

		mesh = new Mesh();
		GetComponent<MeshFilter>().mesh = mesh;
		mesh.vertices = vs;
		mesh.uv = newUVs;
		mesh.triangles = ts;
		mesh.normals = newNormals;
	}
}

注：波浪上方的面为曲面，故使用切线求法线。其他面很有规则，并没有使用叉乘的方法。

几何体没有使用UV贴图，newUVs没有赋值。