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//
// "$Id: fl_arc.cxx,v 1.4.2.3.2.8 2004/04/11 04:38:59 easysw Exp $"
//
// Arc functions for the Fast Light Tool Kit (FLTK).
//
// Copyright 1998-2004 by Bill Spitzak and others.
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Library General Public
// License as published by the Free Software Foundation; either
// version 2 of the License, or (at your option) any later version.
//
// This library 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
// Library General Public License for more details.
//
// You should have received a copy of the GNU Library General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
// USA.
//
// Please report all bugs and problems to "fltk-bugs@fltk.org".
//
// Utility for drawing arcs and circles. They are added to
// the current fl_begin/fl_vertex/fl_end path.
// Incremental math implementation:
#include <FL/fl_draw.H>
#include <FL/math.h>
void fl_arc(double x, double y, double r, double start, double end) {
// draw start point accurately:
double A = start*(M_PI/180); // Initial angle (radians)
double X = r*cos(A); // Initial displacement, (X,Y)
double Y = -r*sin(A); // from center to initial point
fl_vertex(x+X,y+Y); // Insert initial point
// Maximum arc length to approximate with chord with error <= 0.125
double epsilon; {
double r1 = hypot(fl_transform_dx(r,0), // Horizontal "radius"
fl_transform_dy(r,0));
double r2 = hypot(fl_transform_dx(0,r), // Vertical "radius"
fl_transform_dy(0,r));
if (r1 > r2) r1 = r2; // r1 = minimum "radius"
if (r1 < 2.) r1 = 2.; // radius for circa 9 chords/circle
epsilon = 2*acos(1.0 - 0.125/r1); // Maximum arc angle
}
A = end*(M_PI/180) - A; // Displacement angle (radians)
int i = int(ceil(fabs(A)/epsilon)); // Segments in approximation
if (i) {
epsilon = A/i; // Arc length for equal-size steps
double cos_e = cos(epsilon); // Rotation coefficients
double sin_e = sin(epsilon);
do {
double Xnew = cos_e*X + sin_e*Y;
Y = -sin_e*X + cos_e*Y;
fl_vertex(x + (X=Xnew), y + Y);
} while (--i);
}
}
#if 0 // portable version. X-specific one in fl_vertex.cxx
void fl_circle(double x,double y,double r) {
_fl_arc(x, y, r, r, 0, 360);
}
#endif
//
// End of "$Id: fl_arc.cxx,v 1.4.2.3.2.8 2004/04/11 04:38:59 easysw Exp $".
//
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