SYNOPSIS

#include <qwt_transform.h>

Inherited by QwtLogTransform, QwtNullTransform, and QwtPowerTransform.

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 QwtTransform * copy () 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 (doublevalue) const [virtual]

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

Parameters:

value Value to be bounded

Returns:

value unmodified

Reimplemented in QwtLogTransform.

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

Inverse transformation function

Parameters:

value Value

Returns:

Modified value

See Also:

transform()

Implemented in QwtPowerTransform, QwtLogTransform, and QwtNullTransform.

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

Transformation function

Parameters:

value Value

Returns:

Modified value

See Also:

invTransform()

Implemented in QwtPowerTransform, QwtLogTransform, and QwtNullTransform.

Author

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