Qwt User's Guide: QwtScaleEngine Class Reference

Qwt User's Guide 6.1.3

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QwtScaleEngine Class Referenceabstract

Base class for scale engines. More...

`#include <qwt_scale_engine.h>`

Inheritance diagram for QwtScaleEngine:
[legend]

## 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 reference)
| Specify a reference point. More...
double | reference () const
void | setMargins (double lower, double upper)
| Specify margins at the scale's endpoints. More...
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. More...
void | setTransformation (QwtTransform *)
QwtTransform * | transformation () const

## Protected Member Functions
bool | contains (const QwtInterval &, double val) const
QList< double > | strip (const QList< double > &, const QwtInterval &) const
double | divideInterval (double interval, int numSteps) const
QwtInterval | buildInterval (double v) const
| Build an interval around a value. More...

## 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 | r | ) |

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
  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()