utilities/Runtime/MeshUtils.cs

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

namespace KairoEngine.Utility
{
	public static class MeshUtils {
		
		private static readonly Vector3 Vector3zero = Vector3.zero;
		private static readonly Vector3 Vector3one = Vector3.one;
		private static readonly Vector3 Vector3yDown = new Vector3(0,-1);

		
		private static Quaternion[] cachedQuaternionEulerArr;
		private static void CacheQuaternionEuler() {
			if (cachedQuaternionEulerArr != null) return;
			cachedQuaternionEulerArr = new Quaternion[360];
			for (int i=0; i<360; i++) {
				cachedQuaternionEulerArr[i] = Quaternion.Euler(0,0,i);
			}
		}
		private static Quaternion GetQuaternionEuler(float rotFloat) {
			int rot = Mathf.RoundToInt(rotFloat);
			rot = rot % 360;
			if (rot < 0) rot += 360;
			//if (rot >= 360) rot -= 360;
			if (cachedQuaternionEulerArr == null) CacheQuaternionEuler();
			return cachedQuaternionEulerArr[rot];
		}


		public static Mesh CreateEmptyMesh() {
			Mesh mesh = new Mesh();
			mesh.vertices = new Vector3[0];
			mesh.uv = new Vector2[0];
			mesh.triangles = new int[0];
			return mesh;
		}

		public static void CreateEmptyMeshArrays(int quadCount, out Vector3[] vertices, out Vector2[] uvs, out int[] triangles) {
			vertices = new Vector3[4 * quadCount];
			uvs = new Vector2[4 * quadCount];
			triangles = new int[6 * quadCount];
		}
			
		public static Mesh CreateMesh(Vector3 pos, float rot, Vector3 baseSize, Vector2 uv00, Vector2 uv11) {
			return AddToMesh(null, pos, rot, baseSize, uv00, uv11);
		}

		public static Mesh AddToMesh(Mesh mesh, Vector3 pos, float rot, Vector3 baseSize, Vector2 uv00, Vector2 uv11) {
			if (mesh == null) {
				mesh = CreateEmptyMesh();
			}
			Vector3[] vertices = new Vector3[4 + mesh.vertices.Length];
			Vector2[] uvs = new Vector2[4 + mesh.uv.Length];
			int[] triangles = new int[6 + mesh.triangles.Length];
				
			mesh.vertices.CopyTo(vertices, 0);
			mesh.uv.CopyTo(uvs, 0);
			mesh.triangles.CopyTo(triangles, 0);

			int index = vertices.Length / 4 - 1;
			//Relocate vertices
			int vIndex = index*4;
			int vIndex0 = vIndex;
			int vIndex1 = vIndex+1;
			int vIndex2 = vIndex+2;
			int vIndex3 = vIndex+3;

			baseSize *= .5f;

			bool skewed = baseSize.x != baseSize.y;
			if (skewed) {
				vertices[vIndex0] = pos+GetQuaternionEuler(rot)*new Vector3(-baseSize.x,  baseSize.y);
				vertices[vIndex1] = pos+GetQuaternionEuler(rot)*new Vector3(-baseSize.x, -baseSize.y);
				vertices[vIndex2] = pos+GetQuaternionEuler(rot)*new Vector3( baseSize.x, -baseSize.y);
				vertices[vIndex3] = pos+GetQuaternionEuler(rot)*baseSize;
			} else {
				vertices[vIndex0] = pos+GetQuaternionEuler(rot-270)*baseSize;
				vertices[vIndex1] = pos+GetQuaternionEuler(rot-180)*baseSize;
				vertices[vIndex2] = pos+GetQuaternionEuler(rot- 90)*baseSize;
				vertices[vIndex3] = pos+GetQuaternionEuler(rot-  0)*baseSize;
			}
			
			//Relocate UVs
			uvs[vIndex0] = new Vector2(uv00.x, uv11.y);
			uvs[vIndex1] = new Vector2(uv00.x, uv00.y);
			uvs[vIndex2] = new Vector2(uv11.x, uv00.y);
			uvs[vIndex3] = new Vector2(uv11.x, uv11.y);
			
			//Create triangles
			int tIndex = index*6;
			
			triangles[tIndex+0] = vIndex0;
			triangles[tIndex+1] = vIndex3;
			triangles[tIndex+2] = vIndex1;
			
			triangles[tIndex+3] = vIndex1;
			triangles[tIndex+4] = vIndex3;
			triangles[tIndex+5] = vIndex2;
				
			mesh.vertices = vertices;
			mesh.triangles = triangles;
			mesh.uv = uvs;

			//mesh.bounds = bounds;

			return mesh;
		}

		public static void AddToMeshArrays(Vector3[] vertices, Vector2[] uvs, int[] triangles, int index, Vector3 pos, float rot, Vector3 baseSize, Vector2 uv00, Vector2 uv11) {
			//Relocate vertices
			int vIndex = index*4;
			int vIndex0 = vIndex;
			int vIndex1 = vIndex+1;
			int vIndex2 = vIndex+2;
			int vIndex3 = vIndex+3;

			baseSize *= .5f;

			bool skewed = baseSize.x != baseSize.y;
			if (skewed) {
				vertices[vIndex0] = pos+GetQuaternionEuler(rot)*new Vector3(-baseSize.x, 0,  baseSize.z);
				vertices[vIndex1] = pos+GetQuaternionEuler(rot)*new Vector3(-baseSize.x, 0, -baseSize.z);
				vertices[vIndex2] = pos+GetQuaternionEuler(rot)*new Vector3( baseSize.x, 0, -baseSize.z);
				vertices[vIndex3] = pos+GetQuaternionEuler(rot)*baseSize;
			} else {
				vertices[vIndex0] = pos+GetQuaternionEuler(rot-270)*baseSize;
				vertices[vIndex1] = pos+GetQuaternionEuler(rot-180)*baseSize;
				vertices[vIndex2] = pos+GetQuaternionEuler(rot- 90)*baseSize;
				vertices[vIndex3] = pos+GetQuaternionEuler(rot-  0)*baseSize;
			}
			
			//Relocate UVs
			uvs[vIndex0] = new Vector2(uv00.x, uv11.y);
			uvs[vIndex1] = new Vector2(uv00.x, uv00.y);
			uvs[vIndex2] = new Vector2(uv11.x, uv00.y);
			uvs[vIndex3] = new Vector2(uv11.x, uv11.y);
			
			//Create triangles
			int tIndex = index*6;
			
			triangles[tIndex+0] = vIndex0;
			triangles[tIndex+1] = vIndex3;
			triangles[tIndex+2] = vIndex1;
			
			triangles[tIndex+3] = vIndex1;
			triangles[tIndex+4] = vIndex3;
			triangles[tIndex+5] = vIndex2;
		}
	}
}