ref: 3d94702bea267035144836a5929129fd848b4d79
dir: /DoConfig/fltk/src/fl_arc.cxx/
//
// "$Id$"
//
// Arc functions for the Fast Light Tool Kit (FLTK).
//
// Copyright 1998-2010 by Bill Spitzak and others.
//
// This library is free software. Distribution and use rights are outlined in
// the file "COPYING" which should have been included with this file. If this
// file is missing or damaged, see the license at:
//
// http://www.fltk.org/COPYING.php
//
// Please report all bugs and problems on the following page:
//
// http://www.fltk.org/str.php
//
/**
\file fl_arc.cxx
\brief Utility functions for drawing arcs and circles.
*/
// 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>
// avoid problems with some platforms that don't
// implement hypot.
static double _fl_hypot(double x, double y) {
return sqrt(x*x + y*y);
}
void Fl_Graphics_Driver::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 = _fl_hypot(fl_transform_dx(r,0), // Horizontal "radius"
fl_transform_dy(r,0));
double r2 = _fl_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 "$Id$".
//