MATLAB: Ring (annulis) patch

graphicspatchring

Dear friends,
How do I make a 2D ring (annulus) patch? Is it possible to make it as a single patch with a single object handle?
See annulus http://en.wikipedia.org/wiki/Ring_(geometric)
I want plot several 2D objects in a figure. The objects behind the ring should be visible trough the hole, and I want to control the properties of the ring, e.g. with respect to transperancy, color and line style.
Sincerely, Peter.

Best Answer

This might serve your purpose. The function creates an annulus object and allows you to set the linestyle and edgecolor while preserving the correct look of the annulus.
function [P] = annulus(r,R,xf,Xf,yf,Yf)
% Creates a annulus patch object and returns the handle.  Input arguments 
% are the inner radius, outer radius, inner x offset, outer x offset, inner
% y offset and outer Y offset.  Changes to the edgecolor and linestyle are
% allowed, and will preserve the correct look of the annulus
t = linspace(0,2*pi,200);
x = xf + r*cos(t);
y = yf + r*sin(t);
X = Xf + R*cos(t);
Y = Yf + R*sin(t);
P = patch([x X],[y Y],[1,.5,.5],'linestyle','non','facealph',.5);
L(1) = line(x,y,'color','k');
L(2) = line(X,Y,'color','k');
axis equal
plistener(P,'edgecolor',@edgec) % listeners for changes to props.
plistener(P,'linestyle',@lnstl)
      function [] = plistener(ax,prp,func)
          % Sets the properties. From proplistener by Yair Altman.
          psetact = 'PropertyPostSet';
          hC = handle(ax);
          hSrc = hC.findprop(prp);
          hl = handle.listener(hC, hSrc, psetact, {func,ax});
          p = findprop(hC, 'Listeners__');
          if isempty(p)
              p = schema.prop(hC, 'Listeners__', 'handle vector');
              set(p,'AccessFlags.Serialize', 'off', ...
                  'AccessFlags.Copy', 'off',...
                  'FactoryValue', [], 'Visible', 'off');
          end
          hC.Listeners__ = hC.Listeners__(ishandle(hC.Listeners__));
          hC.Listeners__ = [hC.Listeners__; hl];
      end
      function [] = edgec(varargin)
          St = get(varargin{3},'edgecolor');
          set(L,'color',St)
      end
      function [] = lnstl(varargin)
          St = get(varargin{3},'linestyle');
          set(varargin{3},'linestyle','none')
          set(L,'linestyle',St)
      end
end
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