Question

Toolkits usually provide only the most common widgets like buttons, text widgets, scrollbars, sliders etc. No toolkit can provide all possible widgets. wxWidgets has many various widgets; more specialised widgets are created by client programmers.

Custom widgets are created by using the drawing tools provided by the toolkit. There are two possibilities: a programmer can modify or enhance an existing widget, or he can create a custom widget from scratch.

The Burning Widget

This is an example of a widget that we create from scratch. This widget can be found in various media burning applications, like Nero Burning ROM.

widget.h

#ifndef WIDGET_H
#define WIDGET_H

#include <wx/wx.h>

class Widget : public wxPanel
{
public:
  Widget(wxPanel *parent, int id );

  wxPanel *m_parent;


  void OnSize(wxSizeEvent& event);
  void OnPaint(wxPaintEvent& event);  

};

#endif

widget.cpp

#include <wx/wx.h>
#include "widget.h"
#include "burning.h"

int num[] = { 75, 150, 225, 300, 375, 450, 525, 600, 675 };
int asize = sizeof(num)/sizeof(num[1]);

Widget::Widget(wxPanel *parent, int id)
    : wxPanel(parent, id, wxDefaultPosition, wxSize(-1, 30), wxSUNKEN_BORDER)
{
 
  m_parent = parent;

  Connect(wxEVT_PAINT, wxPaintEventHandler(Widget::OnPaint));
  Connect(wxEVT_SIZE, wxSizeEventHandler(Widget::OnSize));

}

void Widget::OnPaint(wxPaintEvent& event)
{
  wxFont font(9, wxFONTFAMILY_DEFAULT, wxFONTSTYLE_NORMAL,
      wxFONTWEIGHT_NORMAL, false, wxT("Courier 10 Pitch"));

  wxPaintDC dc(this);
  dc.SetFont(font);
  wxSize size = GetSize();
  int width = size.GetWidth();

  Burning *burn = (Burning *) m_parent->GetParent();

  int cur_width = burn->GetCurWidth();

  int step = (int) round(width / 10.0);


  int till = (int) ((width / 750.0) * cur_width);
  int full = (int) ((width / 750.0) * 700);


  if (cur_width >= 700) {

    dc.SetPen(wxPen(wxColour(255, 255, 184))); 
    dc.SetBrush(wxBrush(wxColour(255, 255, 184)));
    dc.DrawRectangle(0, 0, full, 30);
    dc.SetPen(wxPen(wxColour(255, 175, 175)));
    dc.SetBrush(wxBrush(wxColour(255, 175, 175)));
    dc.DrawRectangle(full, 0, till-full, 30);

  } else { 

    dc.SetPen(wxPen(wxColour(255, 255, 184)));
    dc.SetBrush(wxBrush(wxColour(255, 255, 184)));
    dc.DrawRectangle(0, 0, till, 30);

  }

  dc.SetPen(wxPen(wxColour(90, 80, 60)));
  for ( int i=1; i <= asize; i++ ) {

  dc.DrawLine(i*step, 0, i*step, 6);
  wxSize size = dc.GetTextExtent(wxString::Format(wxT("%d"), num[i-1]));
  dc.DrawText(wxString::Format(wxT("%d"), num[i-1]), 
    i*step-size.GetWidth()/2, 8);
   }
}

void Widget::OnSize(wxSizeEvent& event)
{
  Refresh();
}

burning.h

#ifndef BURNING_H
#define BURNING_H

#include <wx/wx.h>
#include "widget.h"

class Burning : public wxFrame
{
public:
  Burning(const wxString& title);

  void OnScroll(wxScrollEvent& event);
  int GetCurWidth();

  
  wxSlider *m_slider;
  Widget *m_wid;

  int cur_width;

};

#endif

burning.cpp

#include "burning.h"
#include "widget.h"

int ID_SLIDER = 1;

Burning::Burning(const wxString& title)
     : wxFrame(NULL, wxID_ANY, title, wxDefaultPosition, wxSize(350, 200))
{

  cur_width = 75;

  wxPanel *panel = new wxPanel(this, wxID_ANY);
  wxPanel *centerPanel = new wxPanel(panel, wxID_ANY);

  m_slider = new wxSlider(centerPanel, ID_SLIDER, 75, 0, 750, wxPoint(-1, -1), 
    wxSize(150, -1), wxSL_LABELS);

  wxBoxSizer *vbox = new wxBoxSizer(wxVERTICAL);
  wxBoxSizer *hbox = new wxBoxSizer(wxHORIZONTAL);
  wxBoxSizer *hbox2 = new wxBoxSizer(wxHORIZONTAL);
  wxBoxSizer *hbox3 = new wxBoxSizer(wxHORIZONTAL);

  m_wid = new Widget(panel, wxID_ANY);
  hbox->Add(m_wid, 1, wxEXPAND);

  hbox2->Add(centerPanel, 1, wxEXPAND);
  hbox3->Add(m_slider, 0, wxTOP | wxLEFT, 35);

  centerPanel->SetSizer(hbox3);

  vbox->Add(hbox2, 1, wxEXPAND);
  vbox->Add(hbox, 0, wxEXPAND);

  panel->SetSizer(vbox);
  m_slider->SetFocus();

  Connect(ID_SLIDER, wxEVT_COMMAND_SLIDER_UPDATED, 
    wxScrollEventHandler(Burning::OnScroll)); 

  Centre();

}

void Burning::OnScroll(wxScrollEvent& WXUNUSED(event))
{
 cur_width = m_slider->GetValue();
 m_wid->Refresh();
}


int Burning::GetCurWidth() 
{
 return cur_width;
}

main.h

#include <wx/wx.h>

class MyApp : public wxApp
{
  public:
  virtual bool OnInit();
};

main.cpp

#include "main.h"
#include "burning.h"

IMPLEMENT_APP(MyApp)

bool MyApp::OnInit()
{

  Burning *burning = new Burning(wxT("The Burning Widget"));
  burning->Show(true);

  return true;
}

We put a wxPanel on the bottom of the window and draw the entire widget manually. All the important code resides in the OnPaint() method of the widget class. This widget shows graphically the total capacity of a medium and the free space available to us. The widget is controlled by a slider. The minimum value of our custom widget is 0, the maximum is 750. If we reach value 700, we began drawing in red colour. This indicates overburning.

wxSize size = GetSize();
int width = size.GetWidth();
... 
int till = (int) ((width / 750.0) * cur_width);
int full = (int) ((width / 750.0) * 700);

We draw the widget dynamically. The greater the window, the greater the burning widget. And vice versa. That is why we must calculate the size of the wxPanel onto which we draw the custom widget. The till parameter determines the total size to be drawn. This value comes from the slider widget. It is a proportion of the whole area. The full parameter determines the point, where we begin to draw in red colour. Notice the use of floating point arithmetics. This is to achieve greater precision.

The actual drawing consists of three steps. We draw the yellow or red and yellow rectangle. Then we draw the vertical lines, which divide the widget into several parts. Finally, we draw the numbers, which indicate the capacity of the medium.

void Widget::OnSize(wxSizeEvent& event)
{
  Refresh();
}

Every time the window is resized, we refresh the widget. This causes the widget to repaint itself.

void Burning::OnScroll(wxScrollEvent& WXUNUSED(event))
{
 cur_width = m_slider->GetValue();
 m_wid->Refresh();
}

If we scroll the thumb of the slider, we get the actual value and save it into the cur_width variable. This value is used, when the burning widget is drawn. Then we cause the widget to be redrawn.

Figure: Burning Widget

In this part of the wxWidgets tutorial, we have created a custom widget.