How to resolve the algorithm Animate a pendulum step by step in the C++ programming language

Published on 7 June 2024 03:52 AM
#cpp

How to resolve the algorithm Animate a pendulum step by step in the C++ programming language

Table of Contents

Problem Statement

One good way of making an animation is by simulating a physical system and illustrating the variables in that system using a dynamically changing graphical display. The classic such physical system is a simple gravity pendulum.

Create a simple physical model of a pendulum and animate it.

Let's start with the solution:

Step by Step solution about How to resolve the algorithm Animate a pendulum step by step in the C++ programming language

The code is a C++ program that simulates a pendulum. It has two classes: wxPendulumDlgApp and wxPendulumDlg.

wxPendulumDlgApp is the application class and it creates the main window of the program, which is an instance of wxPendulumDlg.

wxPendulumDlg is the main window class and it contains the code to draw the pendulum and handle the events. The constructor of wxPendulumDlg creates a timer and starts it. The timer calls the OnTimer method every 20 milliseconds, which forces the window to refresh and redraw the pendulum. The wxPendulumDlgPaint method is called when the window needs to be redrawn. It sets the background color of the window to powderblue and draws the pendulum. The pendulum is drawn using a black pen and a black brush. The length of the pendulum is 200 pixels and the initial angle is pi/2 radians. The angle and angular velocity of the pendulum are updated in the OnTimer method using the equations of motion for a pendulum. The wxPendulumDlgSize method is called when the size of the window changes. It calls the Refresh method to redraw the pendulum. The OnClose method is called when the user closes the window. It destroys the window and exits the program.

The code you provided is a C++ program that creates a simple graphical application that simulates a pendulum. The program uses the wxWidgets library to create a window displaying the pendulum and a timer to update the pendulum's position over time.

Here is a detailed explanation of the code:

  1. wxPendulumDlgApp: This class is a derived from wxApp class, which initializes the application and creates the main frame window.

  2. wxPendulumDlg: This class is a derived from wxDialog class, which creates the dialog window that displays the pendulum.

  3. CreateGUIControls(): This method creates the GUI controls for the dialog window.

  4. wxPendulumDlgPaint(wxPaintEvent& event): This method is called when the dialog window needs to be repainted. It draws the pendulum using the wxDC class.

  5. wxPendulumDlgSize(wxSizeEvent& event): This method is called when the dialog window is resized. It updates the size of the pendulum to match the size of the window.

  6. OnTimer(wxTimerEvent& event): This method is called when the timer expires. It updates the pendulum's position and redraws the window.

The program works by first creating a wxPendulumDlg object. This object creates a dialog window with a canvas for drawing the pendulum and a timer for updating the pendulum's position. The timer is started when the dialog window is created and expires every 20 milliseconds. Each time the timer expires, the OnTimer() method is called. This method updates the pendulum's position and redraws the window.

The pendulum's position is updated using the following equation:

m_Angle += m_AngleVelocity * dt;

where:

  • m_Angle is the angle of the pendulum
  • m_AngleVelocity is the angular velocity of the pendulum
  • dt is the time step

The angular acceleration of the pendulum is calculated using the following equation:

angleAccel = (-9.81 / m_uiLength) * sin(m_Angle);

where:

  • angleAccel is the angular acceleration of the pendulum
  • m_uiLength is the length of the pendulum
  • m_Angle is the angle of the pendulum

The program uses a double buffering technique to avoid flickering when the pendulum is moving. Double buffering involves drawing the pendulum to an off-screen buffer first and then copying the buffer to the screen. This prevents the screen from being updated until the entire pendulum has been drawn.

The program is a simple example of how to use wxWidgets to create a graphical application. It can be used as a starting point for creating more complex applications.

Source code in the cpp programming language

#ifndef __wxPendulumDlg_h__
#define __wxPendulumDlg_h__

// ---------------------
/// @author Martin Ettl
/// @date   2013-02-03
// ---------------------

#ifdef __BORLANDC__
#pragma hdrstop
#endif

#ifndef WX_PRECOMP
#include <wx/wx.h>
#include <wx/dialog.h>
#else
#include <wx/wxprec.h>
#endif
#include <wx/timer.h>
#include <wx/dcbuffer.h>
#include <cmath>

class wxPendulumDlgApp : public wxApp
{
    public:
        bool OnInit();
        int OnExit();
};

class wxPendulumDlg : public wxDialog
{
    public:

        wxPendulumDlg(wxWindow *parent, wxWindowID id = 1, const wxString &title = wxT("wxPendulum"), 
				 const wxPoint& pos = wxDefaultPosition, const wxSize& size = wxDefaultSize, 
				 long style = wxSUNKEN_BORDER | wxCAPTION | wxRESIZE_BORDER | wxSYSTEM_MENU | wxDIALOG_NO_PARENT | wxMINIMIZE_BOX | wxMAXIMIZE_BOX | wxCLOSE_BOX);

        virtual ~wxPendulumDlg();
	
		// Event handler
        void wxPendulumDlgPaint(wxPaintEvent& event);
        void wxPendulumDlgSize(wxSizeEvent& event);
        void OnTimer(wxTimerEvent& event);

    private:

		// a pointer to a timer object
        wxTimer *m_timer;

		unsigned int m_uiLength;
		double  	 m_Angle;
		double       m_AngleVelocity;

        enum wxIDs
        {
            ID_WXTIMER1 = 1001,
            ID_DUMMY_VALUE_ 
        };

        void OnClose(wxCloseEvent& event);
        void CreateGUIControls();

        DECLARE_EVENT_TABLE()
};

#endif // __wxPendulumDlg_h__


// ---------------------
/// @author Martin Ettl
/// @date   2013-02-03
// ---------------------

#include "wxPendulumDlg.hpp"
#include <wx/pen.h>

IMPLEMENT_APP(wxPendulumDlgApp)

bool wxPendulumDlgApp::OnInit()
{
    wxPendulumDlg* dialog = new wxPendulumDlg(NULL);
    SetTopWindow(dialog);
    dialog->Show(true);
    return true;
}

int wxPendulumDlgApp::OnExit()
{
    return 0;
}

BEGIN_EVENT_TABLE(wxPendulumDlg, wxDialog)
    EVT_CLOSE(wxPendulumDlg::OnClose)
    EVT_SIZE(wxPendulumDlg::wxPendulumDlgSize)
    EVT_PAINT(wxPendulumDlg::wxPendulumDlgPaint)
    EVT_TIMER(ID_WXTIMER1, wxPendulumDlg::OnTimer)
END_EVENT_TABLE()

wxPendulumDlg::wxPendulumDlg(wxWindow *parent, wxWindowID id, const wxString &title, const wxPoint &position, const wxSize& size, long style)
    : wxDialog(parent, id, title, position, size, style)
{
    CreateGUIControls();
}

wxPendulumDlg::~wxPendulumDlg()
{
}

void wxPendulumDlg::CreateGUIControls()
{
    SetIcon(wxNullIcon);
    SetSize(8, 8, 509, 412);
    Center();

	m_uiLength = 200;
	m_Angle    = M_PI/2.;
	m_AngleVelocity = 0;

    m_timer = new wxTimer();
    m_timer->SetOwner(this, ID_WXTIMER1);
    m_timer->Start(20);
}

void wxPendulumDlg::OnClose(wxCloseEvent& WXUNUSED(event))
{
    Destroy();
}

void wxPendulumDlg::wxPendulumDlgPaint(wxPaintEvent& WXUNUSED(event))
{
    SetBackgroundStyle(wxBG_STYLE_CUSTOM);
    wxBufferedPaintDC dc(this);

    // Get window dimensions
    wxSize sz = GetClientSize();
	// determine the center of the canvas
    const wxPoint center(wxPoint(sz.x / 2, sz.y / 2));

    // create background color
    wxColour powderblue = wxColour(176,224,230);

    // draw powderblue background
    dc.SetPen(powderblue);
    dc.SetBrush(powderblue);
    dc.DrawRectangle(0, 0, sz.x, sz.y);

    // draw lines
	wxPen Pen(*wxBLACK_PEN);
	Pen.SetWidth(1);
    dc.SetPen(Pen);
    dc.SetBrush(*wxBLACK_BRUSH);

    double angleAccel, dt = 0.15;

    angleAccel = (-9.81 / m_uiLength) * sin(m_Angle);
    m_AngleVelocity += angleAccel * dt;
    m_Angle += m_AngleVelocity * dt;

    int anchorX = sz.x / 2, anchorY = sz.y / 4;
    int ballX = anchorX + (int)(sin(m_Angle) * m_uiLength);
    int ballY = anchorY + (int)(cos(m_Angle) * m_uiLength);
    dc.DrawLine(anchorX, anchorY, ballX, ballY);

    dc.SetBrush(*wxGREY_BRUSH);
    dc.DrawEllipse(anchorX - 3, anchorY - 4, 7, 7);

    dc.SetBrush(wxColour(255,255,0)); // yellow
    dc.DrawEllipse(ballX - 7, ballY - 7, 20, 20);
}

void wxPendulumDlg::wxPendulumDlgSize(wxSizeEvent& WXUNUSED(event))
{
    Refresh();
}

void wxPendulumDlg::OnTimer(wxTimerEvent& WXUNUSED(event))
{
	// force refresh
	Refresh();
}

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