create user buttons to change frequency while simulation is running

Hi, My aim is to illustrate lissajous figure of CRO. The concept is to plot a locus of point whose x & y coordinate vary with time. In the code given below I have put x=sin(constant x t) , y=cos(1.5 x constant x t)

if true
Fs = 8000;                   % samples per second
 dt = 1/Fs;                   % seconds per sample
 StopTime = 6.00;             % seconds
 t = (0:dt:StopTime-dt)';     % seconds
 %%Sine wave:
 Fc = 80;                     % hertz
c = -pi:.04:pi;
 cx = sin(pi*Fc*t);
cy = cos(1.5*pi*Fc*t);
figure('color','white');
axis on, axis equal
line(cx, cy, 'color', [.4 .4 .8],'LineWidth',3);
title('sine on x , sine on y ','Color',[.6 0 0])
hold on 
ht=plot(cx,cy,'r.','MarkerSize',20)
while (1)
  for t = 1:length(t)
       x(2) = cx(t);
       y(2) = cy(t);
       set(ht,'XData',x)
      set(ht,'YData',y)
      drawnow
  end
   t = (0:dt:StopTime-dt)';
end
end

ignore 'if true' and 'end' (i wanted my code to appear properly for viewers)

I have 3 questions (1)If you will run this , you will see (other than a nice double boomerang animation) a red dot at origin in graph which I want to avoid. (2)I want to create a slider button for user which replaces 1.5 in above . This way , when slider=1 you will see circle , as frequency multiplies you will see more vertically side by side loops . As frequency diminishes to fraction loop will appear horizontally stacked. (3)Here phase difference is 90 degree . If I gave user freedom to change it via slider dynamically , it will get exciting as the figure will flatten or swell .

Thank You . Eagerly waiting for your valuable suggestions .