Russian Qt Forum

QPainterPath createPath(QPointF cord, QList<QPointF> points)
{
  while (points.count() % 3 != 0)
    points << points.at(points.count() - 1);
          
  QPainterPath path;
  path.moveTo(cord);
  int i = 0;
  while (i + 2 < points.count()){
    path.cubicTo(
      points.at(i), 
      points.at(i + 1), 
      points.at(i + 2)
    );
    i += 3;
  } 
  return path;     
}

bool buildPeriodicSpline( int size, double* t, double* p, double* a, double* b, double* c )
{
	int i;
	//  set up tridiagonal equation system; use coefficient
	//  vectors as temporary buffers
	double* h = new double[size-1];
	double* d = new double[size-1];
	double* s = new double[size];
	for (i = 0; i < size - 1; i++) 
	{
		h[i] = t[i+1] - t[i];
		if (h[i] <= 0) {
			//h[i] = 0.1;
			delete[] h;
			return false;
		}
	}

	const int imax = size - 2;
	double htmp = h[imax];
	double dy1 = (p[0] - p[imax]) / htmp;
	for (i = 1; i < imax; i++)
	{
		b[i] = c[i] = h[i];
		a[i] = 2.0 * (htmp + h[i]);

		const double dy2 = (p[i+1] - p[i]) / h[i];
		d[i] = 6.0 * ( dy1 - dy2);
		dy1 = dy2;
		htmp = h[i];
	}

	//
	// solve it
	//

	// L-U Factorization
	a[0] = sqrt(a[0]);
	c[0] = h[imax] / a[0];
	double sum = 0;

	for(i = 1; i < imax - 1;i++)
	{
		b[i] /= a[i];
		if (i > 0)
			c[i] = - c[i-1] * b[i-1] / a[i]; 
		a[i+1] = sqrt(a[i+1] - b[i]*b[i]);
		sum += c[i]*c[i];
	}
	b[imax-1] = (b[imax-1] - c[imax-2]*b[imax-2])/a[imax-1];
	a[imax] = sqrt(a[imax] - b[imax-1]*b[imax-1] - sum);
	//a[imax] = sqrt(a[imax] - (b[imax-1] - sum)*(b[imax-1] - sum));

	// forward elimination
	//double* s = new double[size];
	s[0] = d[0] / a[0];
	sum = 0;
	for ( i = 1; i < imax; i++)
	{
		s[i] = (d[i] - b[i-1]*s[i-1]) / a[i];
		sum+=c[i-1]*s[i-1];
	}
	s[imax] = (d[imax] - b[imax-1]*s[imax-1] - sum) / a[imax];

	// backward elimination
	s[imax] = - s[imax] / a[imax];
	s[imax-1] = -(s[imax-1]+b[imax-1]*s[imax]) / a[imax-1];
	for (i = imax-2; i >=0; i--)
		s[i] = - (s[i] + b[i] * s[i+1]+c[i]*s[imax]) / a[i];
	

	//
	// Finally, determine the spline coefficients
	//
	s[size-1] = s[0];
	for (i = 0; i < size - 1; i++)
	{
		a[i] = ( s[i+1] - s[i] ) / ( 6.0 * h[i]);
		b[i] = 0.5 * s[i];
		c[i] = ( p[i+1] - p[i] ) / h[i] 
		- (s[i+1] + 2.0 * s[i] ) * h[i] / 6.0; 
	}

	return true;
}

QPointF MainWindow::CatmulRom(QPointF &p1, QPointF &p2, QPointF &p3, QPointF &p4, double &t)
{
    return 0.5*(-t*(1-t)*(1-t)*p1+(2-5*t*t+3*t*t*t)*p2+t*(1+4*t-3*t*t)*p3-t*t*(1-t)*p4);
}

void MainWindow::paintEvent(QPaintEvent *e)
{
    QPainter painter(this);

    QPointF p1(50,50), p2(100,80), p3(150,50), p4(200,100), p5(250,50), p6(300,100);

    painter.setPen(QPen(QBrush(Qt::red),5));
    painter.drawPoint(p1);
    painter.drawPoint(p2);
    painter.drawPoint(p3);
    painter.drawPoint(p4);
    painter.drawPoint(p5);
    painter.drawPoint(p6);

    double tStart=0, tFinish=0;

    int stepCount = 5;
    for(int i=0; i<stepCount; ++i)
    {
        tStart = tFinish;
        tFinish += 1.0/stepCount;
        painter.setPen(Qt::green);
        //сегмент рассчитывается на участке между 2-х внутренних точек
        painter.drawLine(CatmulRom(p1,p1,p2,p3,tStart), CatmulRom(p1,p1,p2,p3,tFinish));  //дублирование первой точки для построения первого сегмента p1-p2
        painter.drawLine(CatmulRom(p1,p2,p3,p4,tStart), CatmulRom(p1,p2,p3,p4,tFinish));  //p2-p3
        painter.drawLine(CatmulRom(p2,p3,p4,p5,tStart), CatmulRom(p2,p3,p4,p5,tFinish));  //p3-p4
        painter.drawLine(CatmulRom(p3,p4,p5,p6,tStart), CatmulRom(p3,p4,p5,p6,tFinish));  //p4-p5
        painter.drawLine(CatmulRom(p4,p5,p6,p6,tStart), CatmulRom(p4,p5,p6,p6,tFinish));  //дублирование последней точки для построения последнего сегмента p5-p6

    }


}