Qwt User's Guide
QwtTransform Class Reference

A transformation between coordinate systems. More...

#include <qwt_transform.h>

Inheritance diagram for QwtTransform:

Public Member Functions

 QwtTransform ()
 Constructor.
virtual ~QwtTransform ()
 Destructor.
virtual double bounded (double value) const
virtual double transform (double value) const =0
virtual double invTransform (double value) const =0
virtual QwtTransformcopy () const =0
 Virtualized copy operation.

Detailed Description

A transformation between coordinate systems.

QwtTransform manipulates values, when being mapped between the scale and the paint device coordinate system.

A transformation consists of 2 methods:

  • transform
  • invTransform

where one is is the inverse function of the other.

When p1, p2 are the boundaries of the paint device coordinates and s1, s2 the boundaries of the scale, QwtScaleMap uses the following calculations:

  • p = p1 + ( p2 - p1 ) * ( T( s ) - T( s1 ) / ( T( s2 ) - T( s1 ) );
  • s = invT ( T( s1 ) + ( T( s2 ) - T( s1 ) ) * ( p - p1 ) / ( p2 - p1 ) );

Member Function Documentation

double QwtTransform::bounded ( double  value) const [virtual]

Modify value to be a valid value for the transformation. The default implementation does nothing.

Parameters:
valueValue to be bounded
Returns:
value unmodified

Reimplemented in QwtLogTransform.

virtual double QwtTransform::invTransform ( double  value) const [pure virtual]

Inverse transformation function

Parameters:
valueValue
Returns:
Modified value
See also:
transform()

Implemented in QwtPowerTransform, QwtLogTransform, and QwtNullTransform.

virtual double QwtTransform::transform ( double  value) const [pure virtual]

Transformation function

Parameters:
valueValue
Returns:
Modified value
See also:
invTransform()

Implemented in QwtPowerTransform, QwtLogTransform, and QwtNullTransform.

List of all members.

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