WiiLab Example Code - BouncingBall

Note:

• MATLAB R2007a or greater is required for this code to run correctly.
• This code is dependent upon several other functions and will not run as a standalone program.

Annotations

Basic steps:

• Establish a connection with the Wiimote

• Initialize figures
  • interactive bouncing ball figure
  • plot to track the ball's position

• Use the yMove function to move the ball up and down in response to the y-acceleration obtained from the Wiimote

• Set a constant x-velocity to the value obtained from the Wiimote's x-accelerometer when swinging the Wiimote to the right

• While the ball is still within the boundaries of the window
  • Use the xMove function to keep the ball moving at a constant horizontal velocity
  • Use the yMove function to move the ball vertically with a constantly decreasing y-velocity
    • special case: When the ball hits the ground, the new y-velocity should account for elasticity and a change in direction
  • Obtain and plot the ball's position

• Close the bouncing ball figure

• Disconnect the Wiimote

Raw Source Code

The source code is also available as a .m file download at the bottom of the page.

function BouncingBall()
%  usage:    BouncingBall()
%  purpose:  Creates an interactive bouncing ball application.
%            Users can lift and throw the ball using the Wiimote
%            and watch it bounce.
%  Note:     The animation is a little off.  If the y-velocity gets low
%            enough, there are little "hiccups" during which the ball's
%            bounce appears to be higher than the previous bounce.

    global xVel;
    global yVel;
    global ball;
    global graph;

    % add the path containing simple graphics functions
    addpath .\EG111-H
    % add the path containing the Wiimote functions
    addpath .\WiimoteFunctions
    % add the path containing the bouncing ball functions
    addpath .\BouncingBallFunctions
    % add the path containing simple graph functions
    addpath .\WiimoteFunctions\GraphingFunctions
    
    % create an instance of the Wiimote
    initializeWiimote();
    
    % initialize a new figure for the bouncing ball interactions
    createWindow(800, 480, 500, 300);
    setTitle('Bouncing Ball');
    bb_figure = gcf;
    
    % if a connection has been established with the Wiimote
    if(isWiimoteConnected())
        % take care of all the basic stuff and prepare the ball for motion
        resetWindow(bb_figure);
        dir3 = 'Press HOME to quit and try again.';
        t3 = text(250, 290, dir3, 'HorizontalAlignment', 'center', 'FontSize', 12);

        % get the ball's location
        [x, y] = getCenter(ball);
        % plot the coordinates of the bottom of the ball
        plot(graph, x, y-10, '*r');

        % while the ball has not yet bounced off the right side of the window
        while(x < 510)
            % if the Wiimote's HOME button is pressed
            if (isButtonPressed('HOME'))
                % clear the current ball
                hide(ball);
                hide(t3);
                % close existing graph
                close(2);
                % and start again
                resetWindow(bb_figure);
                t3 = text(250, 290, dir3, 'HorizontalAlignment', 'center', 'FontSize', 12);
             end %if

            % constant horizontal velocity
            xMove(ball, 0.25*xVel);

            redraw;

            % get the new vertical velocity
            getYVel(y);

            % if the updated y-velocity will put the ball "into the ground",
            % only move it enough so that it will stop when it hits the bottom
            if ((y + yVel) < 10)
                yMove(ball, 10-y);
            % otherwise move it as far as the new y-velocity dictates
            else
                yMove(ball, yVel);
            end %if

            % for smoother animation
            redraw;
            pause(0.001);

            % get the ball's new coordinates
            [x, y] = getCenter(ball);
            % plot the position
            plot(graph, x, y-10, '*r');
            pause(0.001);

        end %while

        hide(t3);
        pause(0.5);

        % close bouncing ball figure
        close(bb_figure);

        % done using the Wiimote
        disconnectWiimote();
    
    % if the Wiimote is not connected
    else
        text(250, 290, 'Wiimote not connected.  Please try again.', ...
            'HorizontalAlignment', 'center', 'FontSize', 12);
        pause(2);
        % close figures
        close;
        close;
        
    end %if
    
end

• BouncingBall.m