QCAD Plugin 开发

QCAD Plugin 开发

eryar@163.com

Abstract. QCAD是基于GPL协议的开源CAD软件，核心功能基于Qt使用C++开发，界面及其交互使用Javascript脚本进行开发。QCAD官方推荐开发其Plugin的方式为使用Javascript脚本的方式，因为QCAD的菜单及其对应的功能全部由Javascript实现。程序有时也需要和C++直接通信，如在QCAD中使用OpenCASCADE。本文主要介绍如何来开发QCAD的插件Plugin，从而能够对QCAD进行扩展，做一些定制化的功能开发。

Key Words. QCAD Plugin, Javascript, C++, CAD, 3D

1.Introduction

QCAD是GPL协议的开源CAD软件，主要使用Javascript脚本进行开发，也可使用C++开发。与AutoCAD的多种开发方式一样，支持AutoLisp脚本，也支持ObjectArx使用C++进行开发。不过开源的程序可以进行源码Debug，遇到问题可以自己动手解决。而AutoCAD是闭源的，如果是正版用户可以咨询开发厂家，不能追根溯源。对于想学习CAD的人来说，建议可以多看这种开源软件，学习CAD的开发原理。

本文主要介绍开源软件QCAD的插件Plugin的开发方法。

2.Javascript

由于QCAD的菜单、交互都提供了Javascript的封装，所以QCAD的大部分功能都是用Javascript脚本实现。使Javascript脚本对QCAD进行开发也是QCAD作者推荐的方式。

https://www.qcad.org/doc/qcad/latest/developer/_script_scope.html

QCAD程序框架提供了一很完整的强大的ECMAScript接口，QCAD几乎所有的功能都可以通过脚本JavaScript来访问。ECMAScript（JavaScript）是很流行且易于学习的一种脚本语言。通过使用JavaScript脚本来扩展QCAD是一种简单高效的方式，扩展的功能包括交互创建、修改工具等等。

用户甚至可以基于QCAD的应用框架开发出一个全新的程序。全新的程序可能是一个控制台工具或包含用户交互的CAD程序：

如下图所示为QCAD中主要模块的功能。Qt主要涉及通用的功能，与CAD没有直接关系。QCAD程序框架QCAD Application Framework提供CAD专用功能，如CAD Core, DXF导入导出、强大的图形视图powerful graphics view等等。脚本ECMAScript可以用来快速的扩展CAD专用功能。QCAD用户接口及所有的交互功能、几乎所有的窗口都是通过脚本实现的。

QCAD包中的qcad.exe就是一个ECMAScript解释器，并且封装了Qt和QCAD的接口。当没有任何ECMAScript脚本的时候，运行qcad.exe将会什么也不做。Qcad.exe默认会查找“scripts/autostart.js”并执行。在QCAD中，autostart.js脚本初始化了所有的ECMAScript工具和用户交互的功能，并启动主程序。

QCAD中几乎所有的窗口、菜单、工具栏都是通过ECMAScript脚本实现。这些脚本位于scripts文件夹中。

用JavaScript脚本开发QCAD插件最好办法就是先在QCAD中创建菜单和工具栏。下面就给出在QCAD中创建菜单和工具栏的步骤。首先要创建文件结构：

l 对于新的顶层菜单，在QCAD目录中的scripts文件夹中创建一个新的文件夹。例如：创建一个“MyScripts”的文件夹；

l 在MyScripts文件夹中创建一个文本文件“MyScripts.js”；

l 在MyScripts文件夹中创建另外一个文件夹来提供一个命令Action，如命名为“MyAction”；

l 在MyAction文件夹中创建一个文本文件MyAction.js，文件名必须和文件夹的名字一致；

文件组织结构如下所示：

将如下JavaScript脚本复制到MyScripts.js文件中：

/**
 * Copyright (c) 2011-2018 by Andrew Mustun. All rights reserved.
 * 
 * This file is part of the QCAD project.
 *
 * QCAD is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * QCAD is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with QCAD.
 */
// MyScripts.js
// All actions are derived from class EAction, so we need to 
// include this class definition here:
include("../EAction.js");
// Constructor calls base class constructor:
function MyScripts(guiAction) {
    EAction.call(this, guiAction);
}
// Derive class MyScripts from class EAction:
MyScripts.prototype = new EAction();
// This static function returns a new or existing QMenu object.
MyScripts.getMenu = function() {
    // EAction.getMenu is a helper function that returns an existing 
    // or new QMenu object with the given title and object name.
    // The object name (here "MyScriptMenu") must be unique. 
    return EAction.getMenu(MyScripts.getTitle(), "MyScriptsMenu");
};
// This static function returns a new or existing QToolBar object.
MyScripts.getToolBar = function() {
    // EAction.getToolBar is a helper function that returns an existing 
    // or new QToolBar object with the given title and object name.
    // The object name (here "MyScriptToolBar") must be unique. 
    return EAction.getToolBar(MyScripts.getTitle(), "MyScriptToolBar");
};
// This static function defines and returns the title of the menu 
// and toolbar.
// The qsTr function marks the title as a translatable string.
MyScripts.getTitle = function() {
    return qsTr("My Scripts");
};
// Init creates the menu and toolbar on start.
MyScripts.init = function() {
    MyScripts.getMenu();
    MyScripts.getToolBar();
};

将如下脚本代码复制到MyAction.js文件中：

/**
 * Copyright (c) 2011-2018 by Andrew Mustun. All rights reserved.
 * 
 * This file is part of the QCAD project.
 *
 * QCAD is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * QCAD is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with QCAD.
 */
// MyAction.js
// Include base class definition:
include("../MyScripts.js");
 
// Constructor calls base class constructor:
function MyAction(guiAction) {
    MyScripts.call(this, guiAction);
}
// Derive class MyAction from class MyScripts:
MyAction.prototype = new MyScripts();
// This function is called immediately after the constructor when the user 
// starts this action. For actions that don't require any user input (for
// example auto zoom), beginEvent does everything and then terminates the
// action.
MyAction.prototype.beginEvent = function() {
    // call base class implementation of beginEvent:
    MyScripts.prototype.beginEvent.call(this);
    // get main application window:
    var appWin = EAction.getMainWindow();
    // print a message in the console of QCAD:
    appWin.handleUserMessage("MyAction() is running...");
    
    // terminate this action immediately:
    this.terminate();
};
// MyAction.init() is called by QCAD to initialize the action and create
// the menu / toolbar for it.
MyAction.init = function(basePath) {
    // Create a new RGuiAction (extended QAction):
    var action = new RGuiAction("&My Action", RMainWindowQt.getMainWindow());
    // This action requires a document to be open. If no document is
    // open, the menu and tool button are grayed out:
    action.setRequiresDocument(true);
    // Define the script file that is executed when this action is
    // launched:
    action.setScriptFile(basePath + "/MyAction.js");
    // Set the icon that is shown in the toolbar and on some platforms
    // also in the menu:
    action.setIcon(basePath + "/MyAction.svg");
    // Set the command(s) that can be used on the command line to 
    // launch this action:
    action.setDefaultCommands(["myaction"]);
    // Define the sort order of this action. Menus and tool buttons are
    // ordered by these values:
    action.setGroupSortOrder(80100);
    action.setSortOrder(200);
    // Set list of widgets this action is added to
    // (menus, tool bars, CAD tool bar panels):
    action.setWidgetNames(["MyScriptsMenu"]);
};

启动QCAD可以发现在菜单上有了MyScripts，如下图所示：

点击MyAction菜单，会在命令窗口中输出测试文字。

3.C++

既然QCAD的是基于Qt开发的，理所当然地应该支持C++开发，只是C++开发方式需要与JavaScript相结合。因为QCAD中一些交互功能封装到JavaScript脚本中了，所以只能通过在JavaScript中调用C++。这种方式QCAD也提供了一个例子，位于源码的

supportexamplesexampleplugin中。主要是将C++的类暴露给JavaScript，使在JavaScript中可以调用C++的类及其方法。只将头文件源码列出如下：RExamplePlugin.h

#include <QDebug>
#include <QObject>
#include <QScriptEngine>
#include <QStringList>

#include "RActionAdapter.h"
#include "RDocumentInterface.h"
#include "RGuiAction.h"
#include "RMainWindow.h"
#include "RPluginInterface.h"

class MyAction : public RActionAdapter {
public:
    MyAction(RGuiAction* guiAction) : RActionAdapter(guiAction) {}

    static void factory(RGuiAction* guiAction) {
        qDebug() << "MyAction::factory";
        if (guiAction==NULL) {
            qDebug("guiAction is NULL");
            return;
        }
        RDocumentInterface* di = RMainWindow::getDocumentInterfaceStatic();

        if (di==NULL) {
            qDebug("di is NULL");
            return;
        }

        di->setCurrentAction(new MyAction(guiAction));
    }

    virtual void beginEvent() {
        qDebug() << "MyAction::beginEvent";
    }
};

class MyClass : public QObject {
Q_OBJECT
public:
    MyClass() : QObject(), i(0), d(0.0) {}

    virtual int getInt() const {
        return i;
    }

    virtual double getDouble() const {
        return d;
    }

    virtual QString getString() const {
        return s;
    }

    virtual void setInt(int v) {
        i = v;
    }

    virtual void setDouble(int v) {
        d = v;
    }

    virtual void setString(const QString& v) {
        s = v;
    }

    void emitSignal() {
        emit mySignal(i);
    }

signals:
    void mySignal(int code);

private:
    int i;
    double d;
    QString s;
};

Q_DECLARE_METATYPE(MyClass*)

/**
 * Script binding for MyClass.
 */
class EcmaMyClass {
public:
    static void initEcma(QScriptEngine& engine);

    static QScriptValue createMyClass(QScriptContext* context, QScriptEngine* engine);
    static QScriptValue myClassToString(QScriptContext *context, QScriptEngine *engine);
    static MyClass* getSelfMyClass(const QString& fName, QScriptContext* context);

    static QScriptValue getInt(QScriptContext* context, QScriptEngine* engine);
    static QScriptValue getDouble(QScriptContext* context, QScriptEngine* engine);
    static QScriptValue getString(QScriptContext* context, QScriptEngine* engine);

    static QScriptValue setInt(QScriptContext* context, QScriptEngine* engine);
    static QScriptValue setDouble(QScriptContext* context, QScriptEngine* engine);
    static QScriptValue setString(QScriptContext* context, QScriptEngine* engine);

    static QScriptValue emitSignal(QScriptContext* context, QScriptEngine* engine);
};



class RExamplePlugin : public QObject, public RPluginInterface
{
    Q_OBJECT
    Q_INTERFACES(RPluginInterface)
#if QT_VERSION >= 0x050000
    Q_PLUGIN_METADATA(IID "org.qcad.exampleplugin")
#endif

public:
    virtual bool init();
    virtual void uninit(bool) {}
    virtual void postInit(InitStatus status);
    virtual void initScriptExtensions(QScriptEngine& engine);
    virtual RPluginInfo getPluginInfo();

};

从上述源码可以看出，通过Qt的Plguin机制将C++的类暴露给JavaScript，从而在JavaScript中使用C++的功能。如下图所示为在QCAD中通过JavaScript调用C++来显示一个三维视图的窗口。

4.Conclusion

综上所述，QCAD二次开发的方式主要是以JavaScript为主。如果要在QCAD中使用C++，或者是使用C++的第三方库，只能是将相关的C++类暴露给JavaScirpt，这样开发才是最简单的。如果纯用C++开发，一些交互功能是封装在JavaScript中，反而效率不高。

通过在QCAD中使用OpenCASCADE之类的三维几何内核，可以实现一些建模、出图的功能。

5.References

1. https://www.qcad.org/doc/qcad/latest/developer/_menus_and_tool_bars.html

2. https://www.qcad.org/doc/qcad/latest/developer/index.html#what_is

3. https://www.qcad.org/rsforum/viewforum.php?f=30&sid=8621b8249232845e54252ef7fa6b34ae

4. JavaScript 高级程序设计

5. C++ GUI Programming with Qt