在线CAD（云CAD）实现自定义实体的详细方法
前言自定义实体在CAD二次开发中使用的频率较高，本章节主要阐述网页CAD中使用自定义实体的方法，mxcad可以根据用户的具体需求来创建和管理自定义实体，可以通过从自定义实体类 McDbCustomEntity()中继承实体的名称、属性、方法，也可结合自身需求对自定义实体类中的属性或方法进行重写。
设置自定义实体
下面以自定义直线为例来介绍如何使用自定义实体，效果如图：
1. 定义自定义实体类继承McDbCustomEntity 类，代码如下：
<span style="background-color: white;"> class McDbTestLineCustomEntity extends McDbCustomEntity {
private pt1: McGePoint3d = new McGePoint3d();
private pt2: McGePoint3d = new McGePoint3d();
constructor(imp?: any) {
super(imp);
}
public create(imp: any) {
return new McDbTestLineCustomEntity(imp)
}
public getTypeName(): string {
return "McDbTestLineCustomEntity";
}
}</span>
2. 通过重写 dwgInFields()函数读取自定义实体数据，dwgOutFields()函数写入自定义实体数据（在从文件读取实体或把实体写入文件时，复制实体等地方都会调用这两个函数），代码如下：
<span style="background-color: white;"> public dwgInFields(filter: IMcDbDwgFiler): boolean {
this.pt1 = filter.readPoint("pt1").val;
this.pt2 = filter.readPoint("pt2").val;
return true;
}
public dwgOutFields(filter: IMcDbDwgFiler): boolean {
filter.writePoint("pt1", this.pt1);
filter.writePoint("pt2", this.pt2);
return true;
}</span>
3. getGripPoints()方法是在点击这个渲染好的图形时提供一个操作点位，即返回自定义的编辑夹点，并在点击操作点移动的回调函数moveGripPointsAt()中处理夹点编辑结果，参考代码如下：<span style="background-color: white;">public moveGripPointsAt(iIndex: number, dXOffset: number, dYOffset: number, dZOffset: number) {
this.assertWrite();
if (iIndex == 0) {
this.pt1.x += dXOffset;
this.pt1.y += dYOffset;
this.pt1.z += dZOffset;
}
else if (iIndex == 1) {
this.pt2.x += dXOffset;
this.pt2.y += dYOffset;
this.pt2.z += dZOffset;
}
};
public getGripPoints(): McGePoint3dArray {
let ret = new McGePoint3dArray()
ret.append(this.pt1);
ret.append(this.pt2);
return ret;
};</span>
4. 每次触发动态绘制worldDraw，就会将原本的实例对象删掉(同时也会删除渲染的three.js物体对象)，通过create方法重新创建实例，参考代码如下：<span style="background-color: white;"> public worldDraw(draw: MxCADWorldDraw): void {
let tmpline = new McDbLine(this.pt1, this.pt2);
draw.drawEntity(tmpline);
}</span>
5. 在程序启动的时候，调用rxInit函数，自定义实体的类型信息注册到系统中，参考代码如下：<span style="background-color: white;"> MxFun.on("mxcadApplicationCreatedMxCADObject", (param) => {
//McDbTestLineCustomEntity 自定义实体
new McDbTestLineCustomEntity().rxInit();
})</span>
完整代码如下：
<span style="background-color: white;">import { IMcDbDwgFiler, McDbCustomEntity, McDbLine, McGePoint3d, McGePoint3dArray, MxCADUiPrPoint, MxCADWorldDraw, MxCpp } from "mxcad";
export class McDbTestLineCustomEntity extends McDbCustomEntity {
private pt1: McGePoint3d = new McGePoint3d();
private pt2: McGePoint3d = new McGePoint3d();
constructor(imp?: any) {
super(imp);
}
public create(imp: any) {
return new McDbTestLineCustomEntity(imp)
}
public getTypeName(): string {
return "McDbTestLineCustomEntity";
}
public dwgInFields(filter: IMcDbDwgFiler): boolean {
this.pt1 = filter.readPoint("pt1").val;
this.pt2 = filter.readPoint("pt2").val;
return true;
}
public dwgOutFields(filter: IMcDbDwgFiler): boolean {
filter.writePoint("pt1", this.pt1);
filter.writePoint("pt2", this.pt2);
return true;
}
public moveGripPointsAt(iIndex: number, dXOffset: number, dYOffset: number, dZOffset: number) {
this.assertWrite();
if (iIndex == 0) {
this.pt1.x += dXOffset;
this.pt1.y += dYOffset;
this.pt1.z += dZOffset;
}
else if (iIndex == 1) {
this.pt2.x += dXOffset;
this.pt2.y += dYOffset;
this.pt2.z += dZOffset;
}
};
public getGripPoints(): McGePoint3dArray {
let ret = new McGePoint3dArray()
ret.append(this.pt1);
ret.append(this.pt2);
return ret;
};
public worldDraw(draw: MxCADWorldDraw): void {
let tmpline = new McDbLine(this.pt1, this.pt2);
draw.drawEntity(tmpline);
}
public setPoint1(pt1: McGePoint3d) {
this.assertWrite();
this.pt1 = pt1.clone();
}
public setPoint2(pt2: McGePoint3d) {
this.assertWrite();
this.pt2 = pt2.clone();
}
public getPoint1() {
return this.pt1;
}
public getPoint2() {
return this.pt2;
}
}
export async function MxTest_DrawCustomEntity() {
let mxcad = MxCpp.getCurrentMxCAD();
const getPoint = new MxCADUiPrPoint();
getPoint.setMessage("\n指定一点:");
let pt1 = (await getPoint.go());
if (!pt1) return;
getPoint.setBasePt(pt1);
getPoint.setUseBasePt(true);
getPoint.setMessage("\n指定二点:");
let pt2 = (await getPoint.go());
if (!pt2) return;
let myline = new McDbTestLineCustomEntity();
myline.setPoint1(pt1);
myline.setPoint2(pt2);
mxcad.drawEntity(myline);
}</span>
实际演练
上面的代码是最简单的画直线的操作，更复杂点的自定义实体例子，可以打开在线DEMO查看，如下图：
首先我们自定义一条自带文本且两个端点以圆结束的直线，其中线段自带的文本可自定义设置，默显示认为线段长度，其实现方法如下：
1. 根据上述自定义实体的方法，我们通过继承 McDbCustomEntity 类来初始化我们的自定义实体，代码如下：
篇幅限制，更多的内容请查询梦想CAD控件
DEMO源码下载地址
https://gitee.com/mxcadx/mxdraw-article/blob/master/%E7%BD%91%E9%A1%B5CAD%E4%BA%8C%E6%AC%A1%E5%BC%80%E5%8F%91%E8%87%AA%E5%AE%9A%E4%B9%89%E5%AE%9E%E4%BD%93/demo.7z
谢谢楼主的分享
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