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描述

点击鼠标左键在屏幕上绘制线段

准备

1. VertexHelper 网格绘制工具类
2. 向量、叉乘
3. RectTransformUtility.ScreenPointToLocalPointInRectangle
4. SetVerticesDirty
5. OnPopulateMesh

思路

1. 鼠标按下，记录线段起点；
2. 鼠标持续按下，记录鼠标当前帧的移动向量；
3. 使用叉乘获取垂直与移动向量的单位向量；
4. 根据设置的宽度获取四个顶点；设置顶点脏数据,更新网格

示例

新建脚本，继承MaskableGraphic；
创建一个Image,移除Image组件，添加新建脚本。
脚本内容如下：

引入命名空间

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

属性

private List<List<UIVertex>> vertexList = new List<List<UIVertex>>();//缓存线段上的网格顶点
private Vector3 lastPoint;//上一帧的点击点
private Vector3 lastLeftPoint;
private Vector3 lastRightPoint;
bool isNewLine;//绘制新的线段
[SerializeField] private float lineWidth = 4f;//线段宽度

方法 绘制网格

protected override void OnPopulateMesh(VertexHelper vh)//绘制网格
{vh.Clear();for (int i = 0; i < vertexList.Count; i++)vh.AddUIVertexQuad(vertexList[i].ToArray());
}

方法 屏幕坐标转为本地坐标

Vector2 ScreenPointToLocalPoint(Vector2 mousePoint)
{var Rect = GetComponent<RectTransform>();Vector2 result = Vector2.zero;switch (canvas.renderMode){case RenderMode.ScreenSpaceOverlay:RectTransformUtility.ScreenPointToLocalPointInRectangle(Rect, mousePoint, null, out result);break;case RenderMode.ScreenSpaceCamera:RectTransformUtility.ScreenPointToLocalPointInRectangle(Rect, mousePoint, canvas.worldCamera, out result);break;case RenderMode.WorldSpace:RectTransformUtility.ScreenPointToLocalPointInRectangle(Rect, mousePoint, canvas.worldCamera, out result);break;}return result;
}

方法 设置网格顶点

private void Update()
{if (Input.GetMouseButtonDown(0))//按下鼠标坐标表示 绘制新的线段{lastPoint = ScreenPointToLocalPoint(Input.mousePosition);//屏幕点转换到当前recttransform上的点isNewLine = true;vertexList.Clear();//清除上一次绘制的线段 若要保留 可不清除}else{if (Input.GetMouseButton(0)){Vector3 currentPoint = ScreenPointToLocalPoint(Input.mousePosition);Vector3 dir = currentPoint - lastPoint;//移动向量if (dir.magnitude < 10)//移动量过小 不绘制网格return;Vector3 normal = Vector3.Cross(dir.normalized, transform.forward);//移动向量和当前ui的朝向 进行叉乘if (isNewLine){isNewLine = false;lastLeftPoint = lastPoint + normal * lineWidth;//绘制新的线段时 作为左侧起点lastRightPoint = lastPoint - normal * lineWidth;}Vector3 leftPoint = currentPoint + normal * lineWidth;//当前线段的左侧终点Vector3 rightPoint = currentPoint - normal * lineWidth;List<UIVertex> ver = new List<UIVertex>();UIVertex uIVertex = new UIVertex();//网格顶点列表uIVertex.position = lastLeftPoint;uIVertex.color = color;ver.Add(uIVertex);UIVertex uIVertex2 = new UIVertex();uIVertex2.position = lastRightPoint;uIVertex2.color = color;ver.Add(uIVertex2);UIVertex uIVertex3 = new UIVertex();uIVertex3.position = rightPoint;uIVertex3.color = color;ver.Add(uIVertex3);UIVertex uIVertex4 = new UIVertex();uIVertex4.position = leftPoint;uIVertex4.color = color;ver.Add(uIVertex4);vertexList.Add(ver);lastLeftPoint = leftPoint;//更新起点 当前帧的终点作为下一帧的起点lastRightPoint = rightPoint;lastPoint = currentPoint;SetVerticesDirty();//设置顶点脏数据 更新网格}}
}