# QwtScaleEngine Class Reference

Base class for scale engines. More...

`#include <qwt_scale_engine.h>`

Inheritance diagram for QwtScaleEngine:
[legend]

List of all members.

## 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

- 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.

See also:
  setAttribute(), testAttribute(), reference(), lowerMargin(), upperMargin()

## Constructor & Destructor Documentation

QwtScaleEngine::QwtScaleEngine | ( |  | ) | `[explicit]`

Constructor.

QwtScaleEngine::~QwtScaleEngine | ( |  | ) | `[virtual]`

Destructor.

## Member Function Documentation

int QwtScaleEngine::attributes | ( |  | ) | const

Return the 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 QwtLinearScaleEngine, and QwtLog10ScaleEngine.

QwtDoubleInterval QwtScaleEngine::buildInterval | ( | double | v | ) | 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,
|  | double | value
| ) |  | const`[protected]`

Check if an interval "contains" a value

Parameters:

  interval | Interval
  value | Value

See also:
  QwtScaleArithmetic::compareEps()

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 | maxMajSteps,
|  | int | maxMinSteps,
|  | double | stepSize = `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 | ( |  | ) | 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 | ( | int | attributes | ) |

Change the scale attribute

Parameters:

  attributes | Set scale attributes

See also:
  Attribute, attributes()

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:
  - QwtLog10ScaleEngine 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

QwtValueList QwtScaleEngine::strip | ( | const QwtValueList & | ticks,
|  | const QwtDoubleInterval & | 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

Check if a attribute is set.

Parameters:

  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 | ( |  | ) | const

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

See also:
  setMargins()