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

NAME

QwtScaleEngine -

SYNOPSIS

#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


QwtScaleEngine ()
 
virtual ~QwtScaleEngine ()
 
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
 
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
 

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()

Member Function Documentation

int QwtScaleEngine::attributes () const

Return 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
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 QwtLog10ScaleEngine, and QwtLinearScaleEngine.

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
Parameters:
interval Interval
 
value Value
See also:
QwtScaleArithmetic::compareEps()

double QwtScaleEngine::divideInterval (doubleintervalSize, intnumSteps) 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 (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 QwtLog10ScaleEngine, and QwtLinearScaleEngine.

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 ( Attributeattribute, boolon = true)

Change a scale attribute
Parameters:
attribute Attribute to change
 
on On/Off
See also:
Attribute, testAttribute()

void QwtScaleEngine::setAttributes (intattributes)

Change the scale attribute
Parameters:
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.
Warning:
•
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:
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 ( Attributeattribute) 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 QwtLog10ScaleEngine, and QwtLinearScaleEngine.

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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Tue Nov 20 2012 Version 5.2.3