92 lines
2.9 KiB
C++
92 lines
2.9 KiB
C++
//
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// "$Id: fl_arc.cxx 7903 2010-11-28 21:06:39Z matt $"
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//
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// Arc functions for the Fast Light Tool Kit (FLTK).
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//
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// Copyright 1998-2010 by Bill Spitzak and others.
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//
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// This library is free software; you can redistribute it and/or
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// modify it under the terms of the GNU Library General Public
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// License as published by the Free Software Foundation; either
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// version 2 of the License, or (at your option) any later version.
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//
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// This library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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// Library General Public License for more details.
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//
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// You should have received a copy of the GNU Library General Public
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// License along with this library; if not, write to the Free Software
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// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
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// USA.
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//
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// Please report all bugs and problems on the following page:
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//
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// http://www.fltk.org/str.php
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//
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/**
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\file fl_arc.cxx
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\brief Utility functions for drawing arcs and circles.
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*/
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// Utility for drawing arcs and circles. They are added to
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// the current fl_begin/fl_vertex/fl_end path.
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// Incremental math implementation:
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#include <FL/fl_draw.H>
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#include <FL/math.h>
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// avoid problems with some platforms that don't
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// implement hypot.
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static double _fl_hypot(double x, double y) {
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return sqrt(x*x + y*y);
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}
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void Fl_Graphics_Driver::arc(double x, double y, double r, double start, double end) {
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// draw start point accurately:
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double A = start*(M_PI/180); // Initial angle (radians)
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double X = r*cos(A); // Initial displacement, (X,Y)
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double Y = -r*sin(A); // from center to initial point
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fl_vertex(x+X,y+Y); // Insert initial point
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// Maximum arc length to approximate with chord with error <= 0.125
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double epsilon; {
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double r1 = _fl_hypot(fl_transform_dx(r,0), // Horizontal "radius"
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fl_transform_dy(r,0));
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double r2 = _fl_hypot(fl_transform_dx(0,r), // Vertical "radius"
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fl_transform_dy(0,r));
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if (r1 > r2) r1 = r2; // r1 = minimum "radius"
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if (r1 < 2.) r1 = 2.; // radius for circa 9 chords/circle
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epsilon = 2*acos(1.0 - 0.125/r1); // Maximum arc angle
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}
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A = end*(M_PI/180) - A; // Displacement angle (radians)
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int i = int(ceil(fabs(A)/epsilon)); // Segments in approximation
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if (i) {
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epsilon = A/i; // Arc length for equal-size steps
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double cos_e = cos(epsilon); // Rotation coefficients
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double sin_e = sin(epsilon);
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do {
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double Xnew = cos_e*X + sin_e*Y;
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Y = -sin_e*X + cos_e*Y;
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fl_vertex(x + (X=Xnew), y + Y);
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} while (--i);
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}
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}
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#if 0 // portable version. X-specific one in fl_vertex.cxx
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void fl_circle(double x,double y,double r) {
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_fl_arc(x, y, r, r, 0, 360);
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}
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#endif
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//
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// End of "$Id: fl_arc.cxx 7903 2010-11-28 21:06:39Z matt $".
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//
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