4f4a8fc3c7
(to clarify static exception LGPL by changing license references) git-svn-id: file:///fltk/svn/fltk/branches/branch-1.3@8864 ea41ed52-d2ee-0310-a9c1-e6b18d33e121
83 lines
2.3 KiB
C++
83 lines
2.3 KiB
C++
//
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// "$Id$"
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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. Distribution and use rights are outlined in
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// the file "COPYING" which should have been included with this file. If this
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// file is missing or damaged, see the license at:
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//
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// http://www.fltk.org/COPYING.php
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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 "$Id$".
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//
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