QwtBezier Class Reference

An implementation of the de Casteljau’s Algorithm for interpolating Bézier curves. More...

#include <qwt_bezier.h>

Public Member Functions
	QwtBezier (double tolerance=0.5)
	Constructor.
	~QwtBezier ()
	Destructor.
void	setTolerance (double tolerance)
	Set the tolerance.
double	tolerance () const
QPolygonF	toPolygon (const QPointF &p1, const QPointF &cp1, const QPointF &cp2, const QPointF &p2) const
	Interpolate a Bézier curve by a polygon.
void	appendToPolygon (const QPointF &p1, const QPointF &cp1, const QPointF &cp2, const QPointF &p2, QPolygonF &polygon) const
	Interpolate a Bézier curve by a polygon.

Static Public Member Functions
static QPointF	pointAt (const QPointF &p1, const QPointF &cp1, const QPointF &cp2, const QPointF &p2, double t)
	Find a point on a Bézier Curve.

Detailed Description

An implementation of the de Casteljau’s Algorithm for interpolating Bézier curves.

The flatness criterion for terminating the subdivision is based on "Piecewise Linear Approximation of Bézier Curves" by Roger Willcocks ( http://www.rops.org )

This article explains the maths behind in a very nice way: https://jeremykun.com/2013/05/11/bezier-curves-and-picasso

Constructor & Destructor Documentation

QwtBezier()

QwtBezier::QwtBezier

(

double

tolerance = 0.5

)

Constructor.

Parameters

tolerance

Termination criterion for the subdivision

See also

setTolerance()

Member Function Documentation

appendToPolygon()

void QwtBezier::appendToPolygon	(	const QPointF &	p1,
		const QPointF &	cp1,
		const QPointF &	cp2,
		const QPointF &	p2,
		QPolygonF &	polygon
	)		const

Interpolate a Bézier curve by a polygon.

appendToPolygon() is tailored for cumulating points from a sequence of bezier curves like being created by a spline interpolation.

Parameters

p1	Start point
cp1	First control point
cp2	Second control point
p2	End point
polygon	Polygon, where the interpolating points are added

Note

If the last point of the incoming polygon matches p1 it won't be inserted a second time.

pointAt()

QPointF QwtBezier::pointAt ( const QPointF &  p1, const QPointF &  cp1, const QPointF &  cp2, const QPointF &  p2, double  t  )

static

Find a point on a Bézier Curve.

Parameters

p1	Start point
cp1	First control point
cp2	Second control point
p2	End point
t	Parameter value, something between [0,1]

Returns

Point on the curve

setTolerance()

void QwtBezier::setTolerance

(

double

tolerance

)

Set the tolerance.

The tolerance is a measurement for the flatness of a curve. A curve with a flatness below the tolerance is considered as being flat terminating the subdivision algorithm.

When interpolating a Bezier curve to render it as a sequence of lines to some sort of raster ( f.e to screen ) a value of 0.5 of the pixel size is a good value for the tolerance.

Parameters

tolerance

Termination criterion for the subdivision

See also

tolerance()

tolerance()

double QwtBezier::tolerance ( ) const

inline

Returns

Tolerance, that is used as criterion for the subdivision

See also

setTolerance()

toPolygon()

QPolygonF QwtBezier::toPolygon	(	const QPointF &	p1,
		const QPointF &	cp1,
		const QPointF &	cp2,
		const QPointF &	p2
	)		const

Interpolate a Bézier curve by a polygon.

Parameters

p1	Start point
cp1	First control point
cp2	Second control point
p2	End point

Returns

Interpolating polygon

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The documentation for this class was generated from the following files:

• /home/runner/work/QWT/QWT/src/qwt_bezier.h
• /home/runner/work/QWT/QWT/src/qwt_bezier.cpp