/*!
\brief Calculate a scale division for an interval
\param x1 First interval limit
\param x2 Second interval limit
\param maxMajorSteps Maximum for the number of major steps
\param maxMinorSteps Maximum number of minor steps
\param stepSize Step size. If stepSize == 0, the engine
calculates one.
\return Calculated scale division
*/
QwtScaleDiv QwtLogScaleEngine::divideScale( double x1, double x2,
int maxMajorSteps, int maxMinorSteps, double stepSize ) const
{
QwtInterval interval = QwtInterval( x1, x2 ).normalized();
interval = interval.limited( LOG_MIN, LOG_MAX );
if ( interval.width() <= 0 )
return QwtScaleDiv();
const double logBase = base();
if ( interval.maxValue() / interval.minValue() < logBase )
{
// scale width is less than one decade -> build linear scale
QwtLinearScaleEngine linearScaler;
linearScaler.setAttributes( attributes() );
linearScaler.setReference( reference() );
linearScaler.setMargins( lowerMargin(), upperMargin() );
if ( stepSize != 0.0 )
{
if ( stepSize < 0.0 )
stepSize = -qPow( logBase, -stepSize );
else
stepSize = qPow( logBase, stepSize );
}
return linearScaler.divideScale( x1, x2,
maxMajorSteps, maxMinorSteps, stepSize );
}
stepSize = qAbs( stepSize );
if ( stepSize == 0.0 )
{
if ( maxMajorSteps < 1 )
maxMajorSteps = 1;
stepSize = divideInterval(
qwtLogInterval( logBase, interval ).width(), maxMajorSteps );
if ( stepSize < 1.0 )
stepSize = 1.0; // major step must be >= 1 decade
}
QwtScaleDiv scaleDiv;
if ( stepSize != 0.0 )
{
QList<double> ticks[QwtScaleDiv::NTickTypes];
buildTicks( interval, stepSize, maxMinorSteps, ticks );
scaleDiv = QwtScaleDiv( interval, ticks );
}
if ( x1 > x2 )
scaleDiv.invert();
return scaleDiv;
}
/*!
Align and divide an interval
\param maxNumSteps Max. number of steps
\param x1 First limit of the interval (In/Out)
\param x2 Second limit of the interval (In/Out)
\param stepSize Step size (Out)
\sa QwtScaleEngine::setAttribute()
*/
void QwtLogScaleEngine::autoScale( int maxNumSteps,
double &x1, double &x2, double &stepSize ) const
{
if ( x1 > x2 )
qSwap( x1, x2 );
const double logBase = base();
QwtInterval interval( x1 / qPow( logBase, lowerMargin() ),
x2 * qPow( logBase, upperMargin() ) );
if ( interval.maxValue() / interval.minValue() < logBase )
{
// scale width is less than one step -> try to build a linear scale
QwtLinearScaleEngine linearScaler;
linearScaler.setAttributes( attributes() );
linearScaler.setReference( reference() );
linearScaler.setMargins( lowerMargin(), upperMargin() );
linearScaler.autoScale( maxNumSteps, x1, x2, stepSize );
QwtInterval linearInterval = QwtInterval( x1, x2 ).normalized();
linearInterval = linearInterval.limited( LOG_MIN, LOG_MAX );
if ( linearInterval.maxValue() / linearInterval.minValue() < logBase )
{
// the aligned scale is still less than one step
if ( stepSize < 0.0 )
stepSize = -qwtLog( logBase, qAbs( stepSize ) );
else
stepSize = qwtLog( logBase, stepSize );
return;
}
}
double logRef = 1.0;
if ( reference() > LOG_MIN / 2 )
logRef = qMin( reference(), LOG_MAX / 2 );
if ( testAttribute( QwtScaleEngine::Symmetric ) )
{
const double delta = qMax( interval.maxValue() / logRef,
logRef / interval.minValue() );
interval.setInterval( logRef / delta, logRef * delta );
}
if ( testAttribute( QwtScaleEngine::IncludeReference ) )
interval = interval.extend( logRef );
interval = interval.limited( LOG_MIN, LOG_MAX );
if ( interval.width() == 0.0 )
interval = buildInterval( interval.minValue() );
stepSize = divideInterval( qwtLogInterval( logBase, interval ).width(),
qMax( maxNumSteps, 1 ) );
if ( stepSize < 1.0 )
stepSize = 1.0;
if ( !testAttribute( QwtScaleEngine::Floating ) )
interval = align( interval, stepSize );
x1 = interval.minValue();
x2 = interval.maxValue();
if ( testAttribute( QwtScaleEngine::Inverted ) )
{
qSwap( x1, x2 );
stepSize = -stepSize;
}
}