Add a useful package (from Source forge) for octave

[CreaPhase.git] / octave_packages / nurbs-1.3.6 / nrbreverse.m

diff --git a/octave_packages/nurbs-1.3.6/nrbreverse.m b/octave_packages/nurbs-1.3.6/nrbreverse.m
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+function rnrb = nrbreverse(nrb)
+%
+% NRBREVERSE: Reverse the evaluation direction of a NURBS curve or surface.
+% 
+% Calling Sequence:
+% 
+%   rnrb = nrbreverse(nrb);
+% 
+% INPUT:
+% 
+%   nrb                : NURBS data structure, see nrbmak.
+%
+% OUTPUT:
+% 
+%   rnrb       : Reversed NURBS.
+% 
+% Description:
+% 
+%   Utility function to reverse the evaluation direction of a NURBS
+%   curve or surface.
+%
+%    Copyright (C) 2000 Mark Spink
+%
+%    This program is free software: you can redistribute it and/or modify
+%    it under the terms of the GNU General Public License as published by
+%    the Free Software Foundation, either version 2 of the License, or
+%    (at your option) any later version.
+
+%    This program is distributed in the hope that it will be useful,
+%    but WITHOUT ANY WARRANTY; without even the implied warranty of
+%    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+%    GNU General Public License for more details.
+%
+%    You should have received a copy of the GNU General Public License
+%    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+if nargin ~= 1
+  error('Incorrect number of input arguments');
+end
+
+if iscell(nrb.knots)
+ if size(nrb.knots,2) == 3
+  error('The function nrbreverse is not yet ready for volumes')
+ else
+  % reverse a NURBS surface
+  coefs = nrb.coefs(:,:,end:-1:1);
+  rnrb = nrbmak(coefs(:,end:-1:1,:), {1.0-fliplr(nrb.knots{1}),...
+                1.0-fliplr(nrb.knots{2})});
+ end
+
+else
+
+  % reverse a NURBS curve
+  rnrb = nrbmak(fliplr(nrb.coefs), 1.0-fliplr(nrb.knots));
+
+end
+
+end
+
+%!demo
+%! pnts = [0.5 1.5 3.0 7.5 8.5;
+%!         3.0 5.5 1.5 4.0 4.5;
+%!         0.0 0.0 0.0 0.0 0.0];
+%! crv1 = nrbmak(pnts,[0 0 0 1/2 3/4 1 1 1]);
+%! crv2 = nrbreverse(crv1);
+%! fprintf('Knots of the original curve\n')
+%! disp(crv1.knots)
+%! fprintf('Knots of the reversed curve\n')
+%! disp(crv2.knots)
+%! fprintf('Control points of the original curve\n')
+%! disp(crv1.coefs(1:2,:))
+%! fprintf('Control points of the reversed curve\n')
+%! disp(crv2.coefs(1:2,:))
+%! nrbplot(crv1,100)
+%! hold on
+%! nrbplot(crv2,100)
+%! title('The curve and its reverse are the same')
+%! hold off
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