QwtScaleEngine - Man Page

Base class for scale engines.

Synopsis

#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
Layout 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.

Member Enumeration Documentation

enum QwtScaleEngine::Attribute

Layout attributes

See also

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

Enumerator

NoAttribute

No attributes.

IncludeReference

Build a scale which includes the reference() value.

Symmetric

Build a scale which is symmetric to the reference() value.

Floating

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.

Inverted

Turn the scale upside down.

Constructor & Destructor Documentation

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

Constructor

Parameters

base Base of the scale engine

See also

setBase()

Member Function Documentation

QwtScaleEngine::Attributes QwtScaleEngine::attributes () const

Returns

Scale attributes

See also

Attribute, setAttributes(), testAttribute()

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

Align and divide an interval

Parameters

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

Returns

base Base of the scale engine

See also

setBase()

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], otherwide it is [0.5 * v, 1.5 * v]

Parameters

value Initial value

Returns

Calculated interval

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

Check if an interval 'contains' a value

Parameters

interval Interval
value Value

Returns

True, when the value is inside the interval

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

Calculate a step size for an interval size

Parameters

intervalSize Interval size
numSteps Number of steps

Returns

Step size

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

Calculate a scale division.

Parameters

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.

Returns

Calculated scale division

Implemented in QwtLogScaleEngine, QwtLinearScaleEngine, and QwtDateScaleEngine.

double QwtScaleEngine::lowerMargin () const

Returns

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

See also

setMargins()

double QwtScaleEngine::reference () const

Returns

the reference value

See also

setReference(), setAttribute()

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

Change a scale attribute

Parameters

attribute Attribute to change
on On/Off

See also

Attribute, testAttribute()

void QwtScaleEngine::setAttributes (Attributes attributes)

Change the scale attribute

Parameters

attributes Set scale attributes

See also

Attribute, attributes()

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

Parameters

base Base of the engine

See also

base()

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

Specify margins at the scale's endpoints.

Parameters

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.

Warning
  • QwtLogScaleEngine measures the margins in decades.
See also

upperMargin(), lowerMargin()

void QwtScaleEngine::setReference (double reference)

Specify a reference point.

Parameters

reference New reference value

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

See also

Attribute

void QwtScaleEngine::setTransformation (QwtTransform * transform)

Assign a transformation

Parameters

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()

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

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

Parameters

ticks Tick list
interval Interval

Returns

Stripped tick list

bool QwtScaleEngine::testAttribute (Attribute attribute) const

Returns

True, if attribute is enabled.

Parameters

attribute Attribute to be tested

See also

Attribute, setAttribute()

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.

Returns

A clone of the transfomation

See also

setTransformation()

double QwtScaleEngine::upperMargin () const

Returns

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

See also

setMargins()

Author

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Info

Mon Jun 1 2020 Version 6.1.5 Qwt User's Guide