MATLAB: Rotating a circle drawn using rectangle()

animationgame developmentsimulation

Hi, I am drawing circles using rectangle() in a simulation for bouncing balls which has x,y and theta position attributes. I know how to change the position for every time step, how do I change the rotation of the ball? I have seen this link (<http://www.mathworks.com/matlabcentral/newsreader/view_thread/71705)>, but this does not help me, how do I add the rotation inside rectangle() ? Thank you for the help !

Best Answer

You cannot rotate the circles drawn by rectangle(). Even if you could, you would not notice any difference since they're circles.

You said you know how to change the position so if you were not rotating them about their centers, but about some other location, then you know how to do that - you said so. You just calculate the new upper left coordinate and call rectangle with an updated 'Position' vector. So it's not the location of the circle you're asking about, it's the rotation at a given location, and like I said, you can't do that, nor would you notice any difference even if you could.

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Use the rectangle() function to draw each of the circles (yes, seriously). Record the handles as you create them. When it comes time to move one, do not redraw it: instead, just update its Position property.

MATLAB: Plot a small circle moving along a larger semi-circle

well i'd say you were very close but should have tackled the problem from another angle.

%Equation for semi circle
    th = linspace( pi, 0, 100);
    R = 1;  %or whatever radius you want
    x = R*cos(th);
    y = R*sin(th);
%draws the semi circle
    h=line(60*x,60*y,...
            'LineWidth',2) ; 
        axis equal
%ball=rectangle('Position',[-5,60,10,10    ],...
%                   'Curvature',[1,1],...
%                   'FaceColor','b');
th = linspace( pi, 0, 15);
R = 60+5;  %radius of path of center of circle as it rolls around semicircle
x2 = R*cos(th)-5; %offset to LL corner of the rectangle 

y2 = R*sin(th)-5; %offset to LL corner of the rectangle 
      h2=line(x2,y2,...
              'LineWidth',2,'color','r') ; 
          axis equal
  for ind = 1:length(x2)
      ball=rectangle('Position',[x2(ind),y2(ind),10,10],...
                     'Curvature',[1,1],...
                     'FaceColor','b');
  end

What you should have done is thought it as what is the path of the center of the circle and then offset it by where you reference the center of the circle.

Best Answer

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