gm_circ_approx.m

算断裂的

function [verts,codes] = gm_circ_approx(startang, endang, numsubdiv) 
% gm_circ_approx: produce bezier curves to approximate a circular arc
%   [vtx,code] = gm_circ_approx(startang, endang, numsubdiv)
% startang, endang are the starting and ending angles of the
% arc (in radians), numsubdiv is the number of divisions.
% Produce a degree-3 bezier spline curve approximating a unit
% circle arc.

totalarc = endang - startang;
onearc = totalarc / numsubdiv;
p = 1.0 / tan(onearc / 2);
p1 = 1 + 1 / p^2;
alpha = (sqrt(3 * p1 + 1) - 1) / (1.5 * p1);
r1 = sqrt((1-alpha)^2 + (p + alpha / p)^2) / sqrt(1 + p^2);
a1 = atan(alpha / p);
verts = zeros(numsubdiv * 3 + 1, 2);
codes = zeros(numsubdiv * 3 + 1, 1);
for j = 1 : numsubdiv
  baseang = startang + onearc * (j - 1);
  ang1 = baseang + a1;
  ang2 = baseang + onearc - a1;
  verts(3 * j - 2, :) = [cos(baseang), sin(baseang)];
  verts(3 * j - 1, :) = [r1 * cos(ang1), r1 * sin(ang1)];
  verts(3 * j, :) = [r1 * cos(ang2), r1 * sin(ang2)];
  if j == 1
    codes(3 * j - 2 : 3 * j) = [1;3;3];
  else
    codes(3 * j - 2 : 3 * j) = [2;3;3];
  end
  verts(3 * numsubdiv + 1,:) = [cos(endang),sin(endang)];
  codes(3 * numsubdiv + 1) = 1;
end
 

% ------------------------------------------------------------------
% Copyright (c) 1999 by Cornell University.  All rights reserved.
% See the accompanying file 'Copyright' for authorship information,
% the terms of the license governing this software, and disclaimers
% concerning this software.
% ------------------------------------------------------------------
% This file is part of the QMG software.  
% Version 2.0 of QMG, release date September 3, 1999
% ------------------------------------------------------------------