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QwtScaleEngine(3) Qwt User's Guide QwtScaleEngine(3)


QwtScaleEngine - Base class for scale engines.


#include <qwt_scale_engine.h>

Inherited by QwtLinearScaleEngine, and QwtLogScaleEngine.

Public Types

enum Attribute { NoAttribute = 0x00, IncludeReference = 0x01, Symmetric = 0x02, Floating = 0x04, Inverted = 0x08 }
typedef QFlags< Attribute > Attributes

Public Member Functions

QwtScaleEngine (uint base=10)
virtual ~QwtScaleEngine ()
Destructor. void setBase (uint base)
uint base () const
void setAttribute (Attribute, bool on=true)
bool testAttribute (Attribute) const
void setAttributes (Attributes)
Attributes attributes () const
void setReference (double)
Specify a reference point. double reference () const
void setMargins (double lower, double upper)
Specify margins at the scale's endpoints. double lowerMargin () const
double upperMargin () const
virtual void autoScale (int maxNumSteps, double &x1, double &x2, double &stepSize) const =0
virtual QwtScaleDiv divideScale (double x1, double x2, int maxMajorSteps, int maxMinorSteps, double stepSize=0.0) const =0
Calculate a scale division. void setTransformation (QwtTransform *)
QwtTransform * transformation () const

Protected Member Functions

bool contains (const QwtInterval &, double value) const
QList< double > strip (const QList< double > &, const QwtInterval &) const
double divideInterval (double intervalSize, int numSteps) const
QwtInterval buildInterval (double value) const
Build an interval around a value.

Detailed Description

Base class for scale engines.

A scale engine tries to find 'reasonable' ranges and step sizes for scales.

The layout of the scale can be varied with setAttribute().

Qwt offers implementations for logarithmic and linear scales.

Definition at line 45 of file qwt_scale_engine.h.

Member Typedef Documentation

typedef QFlags<Attribute > QwtScaleEngine::Attributes

An ORed combination of Attribute values.

Definition at line 78 of file qwt_scale_engine.h.

Member Enumeration Documentation

enum QwtScaleEngine::Attribute

Layout attributes

See also

setAttribute(), testAttribute(), reference(), lowerMargin(), upperMargin()


No attributes.
Build a scale which includes the reference() value.
Build a scale which is symmetric to the reference() value.
The endpoints of the scale are supposed to be equal the outmost included values plus the specified margins (see setMargins()). If this attribute is not set, the endpoints of the scale will be integer multiples of the step size.
Turn the scale upside down.

Definition at line 54 of file qwt_scale_engine.h.

Constructor & Destructor Documentation

QwtScaleEngine::QwtScaleEngine (uint base = 10) [explicit]



base Base of the scale engine

See also


Definition at line 222 of file qwt_scale_engine.cpp.

Member Function Documentation

QwtScaleEngine::Attributes QwtScaleEngine::attributes () const


Scale attributes

See also

Attribute, setAttributes(), testAttribute()

Definition at line 451 of file qwt_scale_engine.cpp.

virtual void QwtScaleEngine::autoScale (int maxNumSteps, double & x1, double & x2, double & stepSize) const [pure virtual]

Align and divide an interval


maxNumSteps Max. number of steps
x1 First limit of the interval (In/Out)
x2 Second limit of the interval (In/Out)
stepSize Step size (Return value)

Implemented in QwtLogScaleEngine, QwtLinearScaleEngine, and QwtDateScaleEngine.

uint QwtScaleEngine::base () const


base Base of the scale engine

See also


Definition at line 500 of file qwt_scale_engine.cpp.

QwtInterval QwtScaleEngine::buildInterval (double value) const [protected]

Build an interval around a value. In case of v == 0.0 the interval is [-0.5, 0.5], otherwise it is [0.5 * v, 1.5 * v]


value Initial value


Calculated interval

Definition at line 395 of file qwt_scale_engine.cpp.

bool QwtScaleEngine::contains (const QwtInterval & interval, double value) const [protected]

Check if an interval 'contains' a value


interval Interval
value Value


True, when the value is inside the interval

Definition at line 341 of file qwt_scale_engine.cpp.

double QwtScaleEngine::divideInterval (double intervalSize, int numSteps) const [protected]

Calculate a step size for an interval size


intervalSize Interval size
numSteps Number of steps


Step size

Definition at line 326 of file qwt_scale_engine.cpp.

virtual QwtScaleDiv QwtScaleEngine::divideScale (double x1, double x2, int maxMajorSteps, int maxMinorSteps, double stepSize = 0.0) const [pure virtual]

Calculate a scale division.


x1 First interval limit
x2 Second interval limit
maxMajorSteps Maximum for the number of major steps
maxMinorSteps Maximum number of minor steps
stepSize Step size. If stepSize == 0.0, the scaleEngine calculates one.


Calculated scale division

Implemented in QwtLogScaleEngine, QwtLinearScaleEngine, and QwtDateScaleEngine.

double QwtScaleEngine::lowerMargin () const


the margin at the lower end of the scale The default margin is 0.

See also


Definition at line 280 of file qwt_scale_engine.cpp.

double QwtScaleEngine::reference () const


the reference value

See also

setReference(), setAttribute()

Definition at line 474 of file qwt_scale_engine.cpp.

void QwtScaleEngine::setAttribute (Attribute attribute, bool on = true)

Change a scale attribute


attribute Attribute to change
on On/Off

See also

Attribute, testAttribute()

Definition at line 417 of file qwt_scale_engine.cpp.

void QwtScaleEngine::setAttributes (Attributes attributes)

Change the scale attribute


attributes Set scale attributes

See also

Attribute, attributes()

Definition at line 442 of file qwt_scale_engine.cpp.

void QwtScaleEngine::setBase (uint base)

Set the base of the scale engine

While a base of 10 is what 99.9% of all applications need certain scales might need a different base: f.e 2

The default setting is 10


base Base of the engine

See also


Definition at line 491 of file qwt_scale_engine.cpp.

void QwtScaleEngine::setMargins (double lower, double upper)

Specify margins at the scale's endpoints.


lower minimum distance between the scale's lower boundary and the smallest enclosed value
upper minimum distance between the scale's upper boundary and the greatest enclosed value

Margins can be used to leave a minimum amount of space between the enclosed intervals and the boundaries of the scale.


QwtLogScaleEngine measures the margins in decades.

See also

upperMargin(), lowerMargin()

Definition at line 312 of file qwt_scale_engine.cpp.

void QwtScaleEngine::setReference (double reference)

Specify a reference point.


reference New reference value

The reference point is needed if options IncludeReference or Symmetric are active. Its default value is 0.0.

See also


Definition at line 465 of file qwt_scale_engine.cpp.

void QwtScaleEngine::setTransformation (QwtTransform * transform)

Assign a transformation


transform Transformation

The transformation object is used as factory for clones that are returned by transformation()

The scale engine takes ownership of the transformation.

See also

QwtTransform::copy(), transformation()

Definition at line 248 of file qwt_scale_engine.cpp.

QList< double > QwtScaleEngine::strip (const QList< double > & ticks, const QwtInterval & interval) const [protected]

Remove ticks from a list, that are not inside an interval


ticks Tick list
interval Interval


Stripped tick list

Definition at line 364 of file qwt_scale_engine.cpp.

bool QwtScaleEngine::testAttribute (Attribute attribute) const


True, if attribute is enabled.


attribute Attribute to be tested

See also

Attribute, setAttribute()

Definition at line 431 of file qwt_scale_engine.cpp.

QwtTransform * QwtScaleEngine::transformation () const

Create and return a clone of the transformation of the engine. When the engine has no special transformation NULL is returned, indicating no transformation.


A clone of the transformation

See also


Definition at line 265 of file qwt_scale_engine.cpp.

double QwtScaleEngine::upperMargin () const


the margin at the upper end of the scale The default margin is 0.

See also


Definition at line 291 of file qwt_scale_engine.cpp.


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