QwtScaleEngine(3) Base class for scale engines.


#include <qwt_scale_engine.h>

Inherited by QwtLinearScaleEngine, and QwtLog10ScaleEngine.

Public Types

enum Attribute { NoAttribute = 0, IncludeReference = 1, Symmetric = 2, Floating = 4, Inverted = 8 }

Public Member Functions

int attributes () const

virtual void autoScale (int maxNumSteps, double &x1, double &x2, double &stepSize) const =0

virtual QwtScaleDiv divideScale (double x1, double x2, int maxMajSteps, int maxMinSteps, double stepSize=0.0) const =0

double lowerMargin () const

QwtScaleEngine ()

double reference () const

void setAttribute (Attribute, bool on=true)

void setAttributes (int)

void setMargins (double lower, double upper)

void setReference (double reference)

bool testAttribute (Attribute) const

virtual QwtScaleTransformation * transformation () const =0

double upperMargin () const

virtual ~QwtScaleEngine ()

Protected Member Functions

QwtDoubleInterval buildInterval (double v) const

bool contains (const QwtDoubleInterval &, double val) const

double divideInterval (double interval, int numSteps) const

QwtValueList strip (const QwtValueList &, const QwtDoubleInterval &) const

Detailed Description

Base class for scale engines.

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

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

Qwt offers implementations for logarithmic (log10) and linear scales. Contributions for other types of scale engines (date/time, log2 ... ) are welcome.

Member Enumeration Documentation

enum QwtScaleEngine::Attribute.IP • 2


 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.

See also:

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

Constructor & Destructor Documentation

QwtScaleEngine::QwtScaleEngine () [explicit]


QwtScaleEngine::~QwtScaleEngine () [virtual]


Member Function Documentation

int QwtScaleEngine::attributes () constReturn the scale attributes

See also:

Attribute, setAttributes(), testAttribute()

virtual void QwtScaleEngine::autoScale (intmaxNumSteps, 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 QwtLinearScaleEngine, and QwtLog10ScaleEngine.

QwtDoubleInterval QwtScaleEngine::buildInterval (doublev) const [protected]

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

bool QwtScaleEngine::contains (const QwtDoubleInterval &interval, doublevalue) const [protected]Check if an interval 'contains' a value


interval Interval
value Value

See also:


double QwtScaleEngine::divideInterval (doubleintervalSize, intnumSteps) const [protected]Calculate a step size for an interval size


intervalSize Interval size
numSteps Number of steps


Step size

virtual QwtScaleDiv QwtScaleEngine::divideScale (doublex1, doublex2, intmaxMajSteps, intmaxMinSteps, doublestepSize = 0.0) const [pure virtual]

Calculate a scale division. Parameters:

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

Implemented in QwtLinearScaleEngine, and QwtLog10ScaleEngine.

double QwtScaleEngine::lowerMargin () constReturns:

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

See also:


double QwtScaleEngine::reference () constReturns:

the reference value

See also:

setReference(), setAttribute()

void QwtScaleEngine::setAttribute (Attributeattribute, boolon = true)Change a scale attribute


attribute Attribute to change
on On/Off

See also:

Attribute, testAttribute()

void QwtScaleEngine::setAttributes (intattributes)Change the scale attribute


attributes Set scale attributes

See also:

Attribute, attributes()

void QwtScaleEngine::setMargins (doublelower, doubleupper)

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.


  • QwtLog10ScaleEngine measures the margins in decades.

See also:

upperMargin(), lowerMargin()

void QwtScaleEngine::setReference (doubler)

Specify a reference point. Parameters:

r new reference value

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

See also:


QwtValueList QwtScaleEngine::strip (const QwtValueList &ticks, const QwtDoubleInterval &interval) const [protected]Remove ticks from a list, that are not inside an interval


ticks Tick list
interval Interval


Stripped tick list

bool QwtScaleEngine::testAttribute (Attributeattribute) constCheck if a attribute is set.


attribute Attribute to be tested

See also:

Attribute, setAttribute()

virtual QwtScaleTransformation* QwtScaleEngine::transformation () const [pure virtual]Returns:

a transformation

Implemented in QwtLinearScaleEngine, and QwtLog10ScaleEngine.

double QwtScaleEngine::upperMargin () constReturns:

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

See also:



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