Drawing on a panel with a DC

If you want to do drawing using software rendering on a wxPanel, this code snippet should get you started :

#include "wx/wx.h"
#include "wx/sizer.h"

class BasicDrawPane : public wxPanel
{
    
public:
    BasicDrawPane(wxFrame* parent);
    
    void paintEvent(wxPaintEvent & evt);
    void paintNow();
    
    void render(wxDC& dc);
    
    // some useful events
    /*
     void mouseMoved(wxMouseEvent& event);
     void mouseDown(wxMouseEvent& event);
     void mouseWheelMoved(wxMouseEvent& event);
     void mouseReleased(wxMouseEvent& event);
     void rightClick(wxMouseEvent& event);
     void mouseLeftWindow(wxMouseEvent& event);
     void keyPressed(wxKeyEvent& event);
     void keyReleased(wxKeyEvent& event);
     */
    
    DECLARE_EVENT_TABLE()
};


class MyApp: public wxApp
{
    bool OnInit();
    
    wxFrame *frame;
    BasicDrawPane * drawPane;
public:
        
};

IMPLEMENT_APP(MyApp)


bool MyApp::OnInit()
{
    wxBoxSizer* sizer = new wxBoxSizer(wxHORIZONTAL);
    frame = new wxFrame((wxFrame *)NULL, -1,  wxT("Hello wxDC"), wxPoint(50,50), wxSize(800,600));
	
    drawPane = new BasicDrawPane( (wxFrame*) frame );
    sizer->Add(drawPane, 1, wxEXPAND);
	
    frame->SetSizer(sizer);
    frame->SetAutoLayout(true);
	
    frame->Show();
    return true;
} 

BEGIN_EVENT_TABLE(BasicDrawPane, wxPanel)
// some useful events
/*
 EVT_MOTION(BasicDrawPane::mouseMoved)
 EVT_LEFT_DOWN(BasicDrawPane::mouseDown)
 EVT_LEFT_UP(BasicDrawPane::mouseReleased)
 EVT_RIGHT_DOWN(BasicDrawPane::rightClick)
 EVT_LEAVE_WINDOW(BasicDrawPane::mouseLeftWindow)
 EVT_KEY_DOWN(BasicDrawPane::keyPressed)
 EVT_KEY_UP(BasicDrawPane::keyReleased)
 EVT_MOUSEWHEEL(BasicDrawPane::mouseWheelMoved)
 */

// catch paint events
EVT_PAINT(BasicDrawPane::paintEvent)

END_EVENT_TABLE()


// some useful events
/*
 void BasicDrawPane::mouseMoved(wxMouseEvent& event) {}
 void BasicDrawPane::mouseDown(wxMouseEvent& event) {}
 void BasicDrawPane::mouseWheelMoved(wxMouseEvent& event) {}
 void BasicDrawPane::mouseReleased(wxMouseEvent& event) {}
 void BasicDrawPane::rightClick(wxMouseEvent& event) {}
 void BasicDrawPane::mouseLeftWindow(wxMouseEvent& event) {}
 void BasicDrawPane::keyPressed(wxKeyEvent& event) {}
 void BasicDrawPane::keyReleased(wxKeyEvent& event) {}
 */

BasicDrawPane::BasicDrawPane(wxFrame* parent) :
wxPanel(parent)
{
}

/*
 * Called by the system of by wxWidgets when the panel needs
 * to be redrawn. You can also trigger this call by
 * calling Refresh()/Update().
 */

void BasicDrawPane::paintEvent(wxPaintEvent & evt)
{
    wxPaintDC dc(this);
    render(dc);
}

/*
 * Alternatively, you can use a clientDC to paint on the panel
 * at any time. Using this generally does not free you from
 * catching paint events, since it is possible that e.g. the window
 * manager throws away your drawing when the window comes to the
 * background, and expects you will redraw it when the window comes
 * back (by sending a paint event).
 */
void BasicDrawPane::paintNow()
{
    wxClientDC dc(this);
    render(dc);
}

/*
 * Here we do the actual rendering. I put it in a separate
 * method so that it can work no matter what type of DC
 * (e.g. wxPaintDC or wxClientDC) is used.
 */
void BasicDrawPane::render(wxDC&  dc)
{
    // draw some text
    dc.DrawText(wxT("Testing"), 40, 60); 
    
    // draw a circle
    dc.SetBrush(*wxGREEN_BRUSH); // green filling
    dc.SetPen( wxPen( wxColor(255,0,0), 5 ) ); // 5-pixels-thick red outline
    dc.DrawCircle( wxPoint(200,100), 25 /* radius */ );
    
    // draw a rectangle
    dc.SetBrush(*wxBLUE_BRUSH); // blue filling
    dc.SetPen( wxPen( wxColor(255,175,175), 10 ) ); // 10-pixels-thick pink outline
    dc.DrawRectangle( 300, 100, 400, 200 );
    
    // draw a line
    dc.SetPen( wxPen( wxColor(0,0,0), 3 ) ); // black line, 3 pixels thick
    dc.DrawLine( 300, 100, 700, 300 ); // draw line across the rectangle
    
    // Look at the wxDC docs to learn how to draw other stuff
}

To avoid flickering :

• Try bufferred DCs, they are necessary on some platforms. wxBufferedDC and wxAutoBufferedPaintDC might help you.
• Call ->SetDoubleBuffered(true); on the panel (On Windows only?)
• Catch the wxEVT_ERASE_BACKGROUND event
• See this : http://docs.wxwidgets.org/stable/wx_wxwindow.html#wxwindowsetbackgroundstyle

For all details, see article Flicker-Free Drawing