Taking Screenshots with wxWidgets under Mac OS is Really Tricky.

Taking screenshots is a very common task and it was a must for one of my current projects. What was a surprise when I understood that my favourite toolkit can’t do that in cross-platform manner.

It is official bug that wxScreenDC does not work properly under Mac OS and you can’t use Blit() message for copying screen onto wxMemoryDC.

After digging the Internet I found a kind of solution which used OpenGL and created wxWidgets-based class which takes screenshots also under Mac OS. It was really hard task for me because I haven’t used neither Carbon nor Cocoa before. However everything works now and I’m happy.

Here it is:
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How to Create Nice About Box in wxWidgets

After taking a look at wxWidgets samples I noticed that all of them have simple message box instaed of normal about box. However in real applications About dialog is important enough part of GUI.

So, in this post I’m going to tell a bit about creating About boxes for your software.

wxWidgets has builf-in API for creating “standard” dialog boxes. wxAboutBox() function is used for displaying About box and wxAboutDialogInfo object, which contains all necessary information, should be passed to wxAboutBox() function.
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How to Draw Gradient Buttons (wxWidgets Way)

Several days ago I found How to draw gradient buttons post at Native Mobile blog. Looks nice but I think that using GradienFill() is not very convenient because you need to fill all these TRIVERTEX structures. wxWidgets provides more convenient way of drawing gradients by using wxDC::GradientFillLinear(). Here is how it can be done in wxWidgets:
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Getting Acquainted with Document/View Framework – Simple Image Viewer

In my previous posts here and here I showed how to create a simple application which uses Document/View framework. Now I’m going to show more complex example – image viewer with scrolling and selection rectangle. As far as I can see from wxForum, implementation of selection-related functionality is some kind of complex but very useful task.

So, let’s start from simple part. The simplest task here is modification of our wxDocument-related class.

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Getting Acquainted with Document-View architecture – Part II – Simple Text Editor

Today we’ll dig a little bit deeper into Document/View framework provided by wxWidgets and will see how to create a simple text editor using this framework.
We’ll take the source code from the previous article of this series and add some modifications. You will see below that modifications are rather simple and take almost no time.
First of all we have to make wxDocTemplate to handle desired file extensions (in our case it’s TXT).
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Getting Acquainted with Document-View architecture – Part I

A few weeks ago, working on TIFF viewer software, I realized that many developers, who use wxWidgets in their work, spend their time on implementing the functionality which already exists in wxWidgets library. Such tasks as loading/saving documents, edit/copy/paste functionality, separating the GUI from application’s logic, all of them can be performed in a far more simple way than people usually do. Why should I write the code which creates wxFileDialog, checks the current state of application, asks user if he/she wants to save the changes, shows wxFileDialog for saving document into a file and so on? Why should I do everything by hands? Life is too short for spending it to all these things 😉
But there no need to give up because there is a thing (in fact, a set of things ;)) which allow to avoid writing tons of unnecessary code. It is wxWidgets’s Document/View framework.
It is the first article from a set of articles about such an interesting part of wxWidgets as Document/View framework.
As always, I’ll try to explain everything by an example. So, the first step will be creating a skeleton application which utilizes Document/View architecture:

DocViewTestApp.h

#ifndef _DOC_VIEW_TEST_APP_H
#define _DOC_VIEW_TEST_APP_H

#include 
#include 

class DocViewTestApp : public wxApp
{
	wxDocManager * m_DocManager;
public:
	virtual bool OnInit();
	virtual int OnExit();
};

DECLARE_APP(DocViewTestApp)

#endif

DocViewTestApp.cpp

#include "DocViewTestApp.h"
#include "DocViewTestMainFrame.h"

IMPLEMENT_APP(DocViewTestApp);

bool DocViewTestApp::OnInit()
{
	m_DocManager = new wxDocManager;
	m_DocManager->SetMaxDocsOpen(1);

	DocViewTestMainFrame * frame = new DocViewTestMainFrame(m_DocManager, NULL);
	SetTopWindow(frame);
	frame->Centre();
	frame->Show();

	return true;
}

int DocViewTestApp::OnExit()
{
	wxDELETE(m_DocManager);
	return wxApp::OnExit();
}

As you can see, the application class contains a member m_DocManager which is an object of wxDocManager class.

The wxDocManager class is part of the document/view framework supported by wxWidgets, and cooperates with the wxView, wxDocument and wxDocTemplate classes.

DocViewTestMainFrame.h

#ifndef _DOC_VIEW_TEST_MAINFRAME_H
#define _DOC_VIEW_TEST_MAINFRAME_H

#include 
#include 
#include 

#define DocViewTestMainFrameTitle _("DocView Test")

class DocViewTestMainFrame : public wxDocParentFrame
{
	DECLARE_DYNAMIC_CLASS(DocViewTestMainFrame)

	wxAuiManager m_AuiManager;

	void CreateControls();
	wxMenuBar * CreateMenuBar();
public:
	DocViewTestMainFrame();
	DocViewTestMainFrame(wxDocManager * docManager, wxFrame * parent, 
		wxWindowID id = wxID_ANY, 
		const wxString & title = DocViewTestMainFrameTitle);
	~DocViewTestMainFrame();
	bool Create(wxDocManager * docManager, wxFrame * parent, 
		wxWindowID id = wxID_ANY, 
		const wxString & title = DocViewTestMainFrameTitle);

	DECLARE_EVENT_TABLE()
	void OnExit(wxCommandEvent & event);
};

#endif

DocViewTestMainFrame.cpp

#include "DocViewTestMainFrame.h"

IMPLEMENT_DYNAMIC_CLASS(DocViewTestMainFrame, wxDocParentFrame)

BEGIN_EVENT_TABLE(DocViewTestMainFrame, wxDocParentFrame)
EVT_MENU(wxID_EXIT, DocViewTestMainFrame::OnExit)
END_EVENT_TABLE()

DocViewTestMainFrame::DocViewTestMainFrame()
{
}

DocViewTestMainFrame::DocViewTestMainFrame(wxDocManager * docManager, wxFrame * parent, 
	wxWindowID id, const wxString & title)
{
	Create(docManager, parent, id, title);
}

DocViewTestMainFrame::~DocViewTestMainFrame()
{
	m_AuiManager.UnInit();
}

bool DocViewTestMainFrame::Create(wxDocManager * docManager, wxFrame * parent, 
	wxWindowID id, const wxString & title)
{
	bool res = wxDocParentFrame::Create(docManager, parent, id, title, 
		wxDefaultPosition, wxSize(650, 450));
	if(res)
	{
		CreateControls();
	}
	return res;
}

void DocViewTestMainFrame::CreateControls()
{
	SetMenuBar(CreateMenuBar());
	m_AuiManager.SetManagedWindow(this);
	

	m_AuiManager.AddPane(new wxPanel(this, wxID_ANY), 
		wxAuiPaneInfo().CenterPane().Name(_("Canvas")));

	m_AuiManager.Update();
}

wxMenuBar * DocViewTestMainFrame::CreateMenuBar()
{
	wxMenuBar * result = new wxMenuBar;

	wxMenu * fileMenu = new wxMenu;
	fileMenu->Append(wxID_NEW, _("New\tCtrl+N"));
	fileMenu->Append(wxID_OPEN, _("Open\tCtrl+O"));
	fileMenu->AppendSeparator();
	fileMenu->Append(wxID_SAVE, _("Save\tCtrl+S"));
	fileMenu->Append(wxID_SAVEAS, _("Save as..."));
	fileMenu->AppendSeparator();
	fileMenu->Append(wxID_EXIT, _("Exit\tAlt+F4"));

	wxMenu * helpMenu = new wxMenu;
	helpMenu->Append(wxID_ABOUT, _("About..."));

	result->Append(fileMenu, _("File"));
	result->Append(helpMenu, _("Help"));

	return result;
}

void DocViewTestMainFrame::OnExit(wxCommandEvent &event)
{
	Close();
}

Our main frame class is derived from wxDocParentFrame class. wxDocParentFrame provides a default top-level frame for applications which utilize Document/View architecture. It can be used ONLY FOR SDI (Single Document Interface), not MDI (Multiple Document Interface) applications. As you can see, we pass a pointer to wxDocManager object to the constructor of our main frame. Passing of wxDocManager object to the constructor is mandatory because in other way our frame will not be able to load the documents.

Now, after we finished a GUI-related part, we have to create our Document and View classes:

DocViewTestDocument.h

#ifndef _DOC_VIEW_TEST_DOCUMENT_H
#define _DOC_VIEW_TEST_DOCUMENT_H

#include 
#include 

class DocViewTestDocument : public wxDocument
{
	DECLARE_DYNAMIC_CLASS(DocViewTestDocument)
public:
	DocViewTestDocument();
};

#endif

DocViewTestDocument.cpp

#include "DocViewTestDocument.h"

IMPLEMENT_DYNAMIC_CLASS(DocViewTestDocument, wxDocument)

DocViewTestDocument::DocViewTestDocument()
{
	wxLogTrace(wxTraceMask(), wxT("DocViewTestDocument::DocViewTestDocument"));
}

DocViewTestView.h

#ifndef _DOC_VIEW_TEST_VIEW_H
#define _DOC_VIEW_TEST_VIEW_H

#include 
#include 

class DocViewTestView : public wxView
{
	DECLARE_DYNAMIC_CLASS(DocViewTestView)
public:
	DocViewTestView();

	virtual void OnDraw(wxDC* dc);
	virtual void OnUpdate(wxView *sender, wxObject *hint = (wxObject *) NULL);
    virtual bool OnClose(bool deleteWindow = true);
};

#endif

Our DocViewTestView class overrides wxView::OnDraw, wxView::OnUpdate and wxView::OnClose methods.

The default implementation calls wxDocument::Close to close the associated document. Does not delete the view. The application may wish to do some cleaning up operations in this function, if a call to wxDocument::Close succeeded

DocViewTestView.cpp

#include "DocViewTestView.h"

IMPLEMENT_DYNAMIC_CLASS(DocViewTestView, wxView)

DocViewTestView::DocViewTestView()
{
	wxLogTrace(wxTraceMask(), wxT("DocViewTestView::DocViewTestView"));
	SetFrame(wxTheApp->GetTopWindow());
}

void DocViewTestView::OnDraw(wxDC* dc)
{
	wxLogTrace(wxTraceMask(), wxT("DocViewTestView::OnDraw"));
}

void DocViewTestView::OnUpdate(wxView *sender, wxObject *hint)
{
	wxLogTrace(wxTraceMask(), wxT("DocViewTestView::OnUpdate"));
}

bool DocViewTestView::OnClose(bool deleteWindow)
{
	wxLogTrace(wxTraceMask(), wxT("DocViewTestView::OnClose"));
	if (!GetDocument()->Close())
	{
        return false;
	}

	SetFrame(NULL);
    Activate(false);
    return true;
}

As you can see, we associate a top level window of our application with each object of DocViewTestView class. After that DocViewTestView object will receive events from this frame. In fact, we can associate not only wxFrame-derived objects but any wxWindow-derived object, e.g. wxScrolledWindow or wxTextCtrl.

Note that this “frame” is not a wxFrame at all in the generic MDI implementation which uses the notebook pages instead of the frames and this is why this method returns a wxWindow and not a wxFrame.

Now, after we created Document and View classes, we have to create a document template. The wxDocTemplate class is used to model the relationship between a document class and a view class.

DocViewTestApp.cpp

#include "DocViewTestApp.h"
#include "DocViewTestMainFrame.h"
#include "DocViewTestDocument.h"
#include "DocViewTestView.h"
...
bool DocViewTestApp::OnInit()
{
	m_DocManager = new wxDocManager;
	m_DocManager->SetMaxDocsOpen(1);

	wxDocTemplate * docTemplate = new 
		wxDocTemplate(m_DocManager, _("DocViewTest Document"), 
		wxT("*.png;*.bmp;*.tiff;*.tif;*.jpg;*.jpeg"), wxEmptyString,
		wxT("png"), wxT("DocViewTest Doc"), wxT("DocViewTest View"),
		CLASSINFO(DocViewTestDocument), CLASSINFO(DocViewTestView));
	...
}
...

As you can see here, for each wxDocTemplate object we have to specify a wxDocManager, document name (will be displayed in the file filter list of Windows file selectors), wildcard, default directory (we left this field empry by using wxEmptyString), default file extension, document type name, view type name, document and view classes.
Now we can start the application and see how it works:

Skeleton application which uses wxWidgets Document/View Framework

Skeleton application which uses wxWidgets Document/View Framework

For the first look our application does nothing. But it is only “for the first look”. If you select File -> Open menu item, file open dialog will appear and if you select a file, then the title of our main frame will be changed, if you select File -> New menu item, the title of our main frame will be changed to the name of newly created document. Also if you select File -> Save menu item, save file dialog box will appear (but in fact, you will not be able to save the document because this behavior is not specified in our skeleton application).
Also if you perform these tasks:

  • Create new document
  • Open a file
  • Save a file
  • Create new document
  • Close the application

And then will look to “Output” window of your IDE, you will see such messages:

01:54:47: DocViewTestDocument::DocViewTestDocument
01:54:47: DocViewTestView::DocViewTestView
01:54:51: DocViewTestView::OnClose
01:54:51: DocViewTestDocument::DocViewTestDocument
01:54:51: DocViewTestView::DocViewTestView
01:54:51: DocViewTestView::OnUpdate
01:55:02: DocViewTestView::OnClose
01:55:02: DocViewTestDocument::DocViewTestDocument
01:55:02: DocViewTestView::DocViewTestView
01:55:24: DocViewTestView::OnClose

Now you can get an idea about how everything works:

  • When you execute wxID_NEW command, new document is created, then a view for this document is created
  • Then you executed wxID_OPEN command, open file dialog is displayed, after you select a file wxView::OnClose method is called, then view and document are destroyed, new document is created, then a view for this document is created, wxView::OnUpdate method is called.
  • When you exit the application wxView::OnClose method is called, then view and document are destroyed.

All wxDocument-, wxView– and wxDocTemplate-derived objects are deleted automatically when wxDocManager object is destroyed (in our application we destroy it in wxApp::OnExit method).
That is all for today. In the next article I will show how to implement simple loading/saving functionality.

Download the source code for this article.

wxJSON Tutorial – Part IV – Using Comment Lines in wxJSON

Preface

Here is a fourth part of wxJSON tutorial provided by Luciano Cattani, author and maintainer of wxJSON library.

Using Comment Lines in wxJSON

Comments are not supported by the JSON syntax specifications but many JSON implementations do recognize and store comment lines in the JSON value objects. Starting by version 0.2, the wxJSON library do recognize and store C/C++ comment lines in the JSON input text and can also write comments to the JSON output text.
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wxJSON Tutorial – Part III – Describing a Table

Preface

Here is a third part of wxJSON tutorial provided by Luciano Cattani, author and maintainer of wxJSON library.

Describing a Table with wxJSON

How many times did you use a table in your application? I know the answer: many times. So the best thing would be to write a general-purpose panel window that is capable to show every possible table and table’s format.
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wxJSON Tutorial – Part II – Сonfiguration File

Preface

Here is a second part of wxJSON tutorial provided by Luciano Cattani, author and maintainer of wxJSON library.

Creating a Configuration File with wxJSON

We start by using JSON for an application’s configuration file. There are many formats for storing application’s configuration data. I remember when there was MS-DOS: each application used its own, unreadable and proprietary format (it was a nightmare). Next came Windows 3: it had a better way for storing application’s configuration data; they were kept in an .INI file which contains simple ASCII text. This was a good thing because it was easier for humans to fine-tuning application’s behaviour.

In this example we use JSON to store the configuration data of a simple web server application. If you take a look at the Apache config file you will notice that our example looks very similar (but much more human readable).
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