Arc.cpp

// Arc.cpp

// Copyright 2011, Dan Heeks
// This program is released under the BSD license. See the file COPYING for details.

#include "Arc.h"
#include "Curve.h"

void CArc::SetDirWithPoint(const Point& p)
{
	double angs = atan2(m_s.y - m_c.y, m_s.x - m_c.x);
	double ange = atan2(m_e.y - m_c.y, m_e.x - m_c.x);
	double angp = atan2(p.y - m_c.y, p.x - m_c.x);
	if(ange < angs)ange += 6.2831853071795864;
	if(angp < angs - 0.0000000000001)angp += 6.2831853071795864;
	if(angp > ange + 0.0000000000001)m_dir = false;
	else m_dir = true;
}

double CArc::IncludedAngle()const
{
	double angs = atan2(m_s.y - m_c.y, m_s.x - m_c.x);
	double ange = atan2(m_e.y - m_c.y, m_e.x - m_c.x);
	if(m_dir)
	{
		// make sure ange > angs
		if(ange < angs)ange += 6.2831853071795864;
	}
	else
	{
		// make sure angs > ange
		if(angs < ange)angs += 6.2831853071795864;
	}

	return fabs(ange - angs);
}

bool CArc::AlmostALine()const
{
	Point mid_point = MidParam(0.5);
	if(Line(m_s, m_e - m_s).Dist(mid_point) <= Point::tolerance)
		return true;

	const double max_arc_radius = 1.0 / Point::tolerance;
	double radius = m_c.dist(m_s);
	if (radius > max_arc_radius)
	{
		return true;	// We don't want to produce an arc whose radius is too large.
	}

	return false;
}

Point CArc::MidParam(double param)const {
	/// returns a point which is 0-1 along arc
	if(fabs(param) < 0.00000000000001)return m_s;
	if(fabs(param - 1.0) < 0.00000000000001)return m_e;

	Point p;
	Point v = m_s - m_c;
	v.Rotate(param * IncludedAngle());
	p = v + m_c;

	return p;
}

//segments - number of segments per full revolution!
//d_angle - determines the direction and the ammount of the arc to draw
void CArc::GetSegments(void(*callbackfunc)(const double *p), double pixels_per_mm)const
{
	if(m_s == m_e)
		return;

	Point Va = m_s - m_c;
	Point Vb = m_e - m_c;

	double start_angle = atan2(Va.y, Va.x);
	double end_angle = atan2(Vb.y, Vb.x);

	if(m_dir)
	{
		if(start_angle > end_angle)end_angle += 6.28318530717958;
	}
	else
	{
		if(start_angle < end_angle)end_angle -= 6.28318530717958;
	}

	double radius = m_c.dist(m_s);
	double d_angle = end_angle - start_angle;
	int segments = (int)(fabs(pixels_per_mm * radius * d_angle / 6.28318530717958 + 1));

    double theta = d_angle / (double)segments;
	while(theta>1.0){segments*=2;theta = d_angle / (double)segments;}
    double tangetial_factor = tan(theta);
    double radial_factor = 1 - cos(theta);

    double x = radius * cos(start_angle);
    double y = radius * sin(start_angle);

	double pp[3] = {0.0, 0.0, 0.0};

   for(int i = 0; i < segments + 1; i++)
    {
		Point p = m_c + Point(x, y);
		pp[0] = p.x;
		pp[1] = p.y;
		(*callbackfunc)(pp);

        double tx = -y;
        double ty = x;

        x += tx * tangetial_factor;
        y += ty * tangetial_factor;

        double rx = - x;
        double ry = - y;

        x += rx * radial_factor;
        y += ry * radial_factor;
    }
}