# Erase bouncing ball drawn on GUI so there is only one drawn ball on GUI at a time

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Dakota Nielsen on 28 May 2021
Commented: Jan on 28 May 2021
Hey guys, I'm working on this quick project that has a ball bouncing off all the walls continously. I basically have everything running as I want it, but when I draw the ball on the GUI my old drawn balls stay on GUI as well. How could I delete it so there is only one ball drawn on the GUI at a time. This is what I have.
set(gca, 'XLim',[-10 10], 'YLim', [-10 10]);
cla
axis square
ball = animatedline('color' , 'r', 'Marker', 'o' , 'MarkerSize',12,'MarkerFaceColor','r');
theta = pi/6; % Sets Theta
V = 5; %Sets value of V
[x,y,t] = startBall(V,theta,ball); %Calls function to return x,y,t
xr = 10; % x right
xl = -10; % x left
yt = xr; % y top
yb = xl; % y bottom
function[x,y,t] = startBall(V,theta,ball)
dt =0.1 ; % sets time as 0.1
Vx = V * cos(theta);
Vy = V * sin(theta);
x0 = 0; %initial x position
y0 = 0; %initial y position
x = x0;
y = y0;
t = 0; % Time
while 1 == 1
if x(end) > 10 && y(end) > 10 || x(end) < -10 && y(end) < -10 %Condition of the ball hittin CORNER
Vx = -1*Vx %Change Vx velocity from hitting corner
Vy = -1 * Vy; %Change Vy velocity from hitting corner
elseif x(end) > 10 || x(end) < -10 % Checks if Ball is hitting top or bottom
Vx = -1 * Vx;
elseif y(end) > 10 || y(end) < -10 %Checks if ball is hitting left or right
Vy = -1 * Vy;
end
x(end + 1) = x(end) + Vx * dt; % UPDATES X VAL
y(end + 1) = y(end) + Vy * dt; % UPDdATES Y VAL
t(end + 1) = t(end) + dt; %UPDATES T VAL
clearpoints(ball);
drawnow;
pause(.01)
end
end
Jan on 28 May 2021
Just a hint: This can be simplified:
if x(end) > 10 && y(end) > 10 || x(end) < -10 && y(end) < -10 %Condition of the ball hittin CORNER
Vx = -1*Vx %Change Vx velocity from hitting corner
Vy = -1 * Vy; %Change Vy velocity from hitting corner
elseif x(end) > 10 || x(end) < -10 % Checks if Ball is hitting top or bottom
Vx = -1 * Vx;
elseif y(end) > 10 || y(end) < -10 %Checks if ball is hitting left or right
Vy = -1 * Vy;
end
to
if x(end) > 10 || x(end) < -10 % Checks if Ball is hitting top or bottom
Vx = -Vx;
end
if y(end) > 10 || y(end) < -10 %Checks if ball is hitting left or right
Vy = -Vy;
end