Ipelib: ipe::Bezier Class Reference

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Public Member Functions | Static Public Member Functions | Public Attributes | List of all members
ipe::Bezier Class Reference
Ipe Geometry

`#include <ipegeo.h>`

## Public Member Functions
| Bezier ()
| Bezier (const Vector &p0, const Vector &p1, const Vector &p2, const Vector &p3)
Vector | point (double t) const
Vector | tangent (double t) const
double | distance (const Vector &v, double bound)
bool | straight (double precision) const
void | subdivide (Bezier &l, Bezier &r) const
void | approximate (double precision, std::vector< Vector > &result) const
Rect | bbox () const
bool | snap (const Vector &v, double &t, Vector &pos, double &bound) const
void | intersect (const Line &l, std::vector< Vector > &result) const
void | intersect (const Segment &l, std::vector< Vector > &result) const
void | intersect (const Bezier &b, std::vector< Vector > &result) const

## Static Public Member Functions
static Bezier | quadBezier (const Vector &p0, const Vector &p1, const Vector &p2)
static void | oldSpline (int n, const Vector *v, std::vector< Bezier > &result)
static void | spline (int n, const Vector *v, std::vector< Bezier > &result)
static void | closedSpline (int n, const Vector *v, std::vector< Bezier > &result)

## Public Attributes
Vector | iV [4]

## Detailed Description

A cubic Bezier spline.

## Constructor & Destructor Documentation

ipe::Bezier::Bezier | ( |  | ) |
| inline

Default constructor, uninitialized curve.

ipe::Bezier::Bezier | ( | const Vector & | p0,
|  | const Vector & | p1,
|  | const Vector & | p2,
|  | const Vector & | p3
| ) |  |
| inline

Constructor with four control points.

## Member Function Documentation

Vector Bezier::point | ( | double | t | ) | const

Return point on curve with parameter t (from 0.0 to 1.0).

Vector Bezier::tangent | ( | double | t | ) | const

Return tangent direction of curve at parameter t (from 0.0 to 1.0).

The returned vector is not normalized.

Referenced by ipe::Snap::setEdge().

double Bezier::distance | ( | const Vector & | v,
|  | double | bound
| ) |  |

Return distance to Bezier spline.

But may just return bound if actual distance is larger. The Bezier spline is approximated to a precision of 1.0, and the distance to the approximation is returned.

References ipe::Rect::addPoint(), and ipe::Rect::certainClearance().

bool Bezier::straight | ( | double | precision | ) | const

Returns true if the Bezier curve is nearly identical to the line segment iV[0]..iV[3].

References ipe::Line::distance(), and ipe::Line::through().

Referenced by ipe::Arc::intersect(), and snap().

void Bezier::subdivide | ( | Bezier & | l,
|  | Bezier & | r
| ) |  | const

Subdivide this Bezier curve in the middle.

References iV.

Referenced by ipe::Arc::intersect(), and snap().

void Bezier::approximate | ( | double | precision,
|  | std::vector< Vector > & | result
| ) |  | const

Approximate by a polygonal chain.

result must be empty when calling this.

References approximate().

Referenced by approximate().

Rect Bezier::bbox | ( |  | ) | const

Return a tight bounding box (accurate to within 0.5).

References ipe::Rect::addPoint(), ipe::Rect::bottomLeft(), and ipe::Rect::topRight().

Referenced by ipe::BBoxPainter::doCurveTo().

bool Bezier::snap | ( | const Vector & | v,
|  | double & | t,
|  | Vector & | pos,
|  | double & | bound
| ) |  | const

Find (approximately) nearest point on Bezier spline.

Find point on spline nearest to v, but only if it is closer than bound. If a point is found, sets t to the parameter value and pos to the actual point, and returns true.

References ipe::Rect::addPoint(), ipe::Rect::certainClearance(), ipe::Rect::intersects(), ipe::Segment::intersects(), iV, ipe::Segment::project(), ipe::Vector::snap(), snap(), straight(), and subdivide().

Referenced by ipe::Snap::setEdge(), and snap().

Bezier Bezier::quadBezier | ( | const Vector & | p0,
|  | const Vector & | p1,
|  | const Vector & | p2
| ) |  |
| static

Convert a quadratic Bezier-spline to a cubic one.

The quadratic Bezier-spline with control points p0, p1, p2 is identical to the cubic Bezier-spline with control points q0 = p0, q1 = (2p1 + p0)/3, q2 = (2p1 + p2)/3, q3 = p2.

void Bezier::oldSpline | ( | int | n,
|  | const Vector * | v,
|  | std::vector< Bezier > & | result
| ) |  |
| static

Convert an old-style Ipe B-spline to a series of Bezier splines.

For some reason lost in the mist of time, this was the definition of splines in Ipe for many years. It doesn't use knots. The first and last control point are simply given multiplicity 3.

Bezier splines are appended to result.

Referenced by ipe::CurveSegment::beziers().

void Bezier::spline | ( | int | n,
|  | const Vector * | v,
|  | std::vector< Bezier > & | result
| ) |  |
| static

Convert a clamped uniform B-spline to a series of Bezier splines.

See Thomas Sederberg, Computer-Aided Geometric Design, Chapter 6.

In polar coordinates, a control point is defined by three knots, so n control points need n + 2 knots. To clamp the spline to the first and last control point, the first and last knot are repeated three times. This leads to k knot intervals and the knot sequence [0, 0, 0, 1, 2, 3, 4, 5, 6, ..., k-2, k-1, k, k, k] There are k + 5 = n + 2 knots in this sequence, so k = n-3 is the number of knot intervals and therefore the number of output Bezier curves.

If n = 4, the knot sequence is [0, 0, 0, 1, 1, 1] and the result is simply the Bezier curve on the four control points.

When n in {2, 3}, returns a single Bezier curve that is a segment or quadratic Bezier spline. This is different from the behaviour of the "old" Ipe splines.

Bezier splines are appended to result.

Referenced by ipe::CurveSegment::beziers().

void Bezier::closedSpline | ( | int | n,
|  | const Vector * | v,
|  | std::vector< Bezier > & | result
| ) |  |
| static

Convert a closed uniform cubic B-spline to a series of Bezier splines.

Bezier splines are appended to result.

Referenced by ipe::ClosedSpline::beziers().

void Bezier::intersect | ( | const Line & | l,
|  | std::vector< Vector > & | result
| ) |  | const

Compute intersection points of Bezier with Line.

References intersect(), ipe::Segment::intersects(), and ipe::Line::side().

Referenced by intersect().

void Bezier::intersect | ( | const Segment & | l,
|  | std::vector< Vector > & | result
| ) |  | const

Compute intersection points of Bezier with Segment.

References ipe::Segment::iP, and ipe::Segment::iQ.

void Bezier::intersect | ( | const Bezier & | b,
|  | std::vector< Vector > & | result
| ) |  | const

Compute intersection points of Bezier with Bezier.

## Member Data Documentation

Vector ipe::Bezier::iV[4]

Referenced by ipe::Painter::curveTo(), ipe::Arc::intersect(), ipe::Matrix::operator*(), snap(), and subdivide().

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

- ipegeo.h
- ipegeo.cpp