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Thread: Problem with zoomer

  1. 15th April 2012, 16:46 #1
    alainstgt
    alainstgt is offline Novice
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    Default Problem with zoomer

    Qwt 6.0.1 / Qt 4.4.1 / VC++ 9.0 / Win XP

    I have written a graphics module for the SigLib library (Digital Signal Library from Numerix-DSP) and have encountered a problem with the zooming function. I get a memory access violation in my routine handling the return to the zoom base:
    Unhandled exception at 0x1007463a (qwtd.dll) in SigLibGraph.exe: 0xC0000005: Access violation reading location 0xcdcdcded.
    Following the fragment of code where the access violation occured:
    uint QwtPlotZoomer::zoomRectIndex() const
    {
    return d_data->zoomRectIndex;
    }

    d_data seems to have been not initialized, where should I do it?

    Qt Code: 
    1. // main.cpp
    2. // AW - 14.03.2012
    3.  
    4. #include <QApplication>				// Qt library
    5. #include <qwt_plot.h>				// Qwt Plot library
    6. #include <qwt_plot_curve.h>
    7. #include <qwt_math.h>
    8. #include <siglib.h>					// SigLib DSP library 
    9. #include "SigLibGraph.h"			// Qt/Qwt SigLib Graphics library
    10.  
    11. int main( int argc, char * argv[] )
    12. {
    13. 	QApplication app( argc,argv );
    14.  
    15. 	const unsigned int FFT_LENGTH = 512;
    16. 	double *pXData = new double[FFT_LENGTH];
    17. 	double *pResult = new double[FFT_LENGTH];
    18. 	double *pResult2 = new double[FFT_LENGTH];
    19.  
    20.  
    21. 	// fill data arrays
    22. 	for ( unsigned int idx = 0; idx < FFT_LENGTH; idx++ ) {
    23. 		pXData[idx] = double( idx );
    24. 		pResult[idx] = sin( M_PI * 0.02 * double( idx ));
    25. 		pResult2[idx] = cos( M_PI * 0.02 * double( idx ));
    26. 	}
    27.  
    28. 	// plot object
    29. 	Plot2D *myPlot = new Plot2D( "function plot", "time", "amplitude" );
    30. 	myPlot->attachCurve( pXData, pResult, FFT_LENGTH, "sine" );
    31. 	myPlot->attachCurve( pXData, pResult2, FFT_LENGTH, "cosine", Qt::cyan );
    32. 	myPlot->show();
    33.  
    34. 	return app.exec();
    35. }
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    Qt Code: 
    1. /***************************************************************	
    2. 	SigLibGraph.h
    3.  AW - 31.03.2012
    4. ***************************************************************/
    5.  
    6. #ifndef SIGLIBGRAPH_H
    7. #define SIGLIBGRAPH_H
    8.  
    9. #include <siglib.h>					// SigLib DSP library 
    10. #include <qwt_plot.h>				// Qwt library
    11. #include <qwt_plot_grid.h>
    12. #include <qwt_legend.h>
    13. #include <qwt_plot_zoomer.h>
    14.  
    15.  
    16. class Plot2D: public QwtPlot
    17. {
    18. 	Q_OBJECT
    19.  
    20. public:	
    21. 	Plot2D( QString plotTitle = "",
    22. 				QString xLabel = "x-axis",
    23. 				QString yLabel = "y-axis",
    24. 				QWidget *parent = NULL ); 
    25.  
    26. 	void attachCurve( double *xData,
    27. 							double *yData,
    28. 							uint dataCount, 
    29. 							QString curveLabel = "",
    30. 							QColor curveColor = Qt::yellow );
    31.  
    32. 	void setXAxisScale( double firstValue, double lastValue );
    33. 	void setYAxisScale( double firstValue, double lastValue );
    34. 	void setXLogAxis();
    35. 	void setYLogAxis();
    36. 	void setBackgroundColor( QColor backgroundColor );
    37.  
    38. public Q_SLOTS:
    39.     void autoRescale( QRectF );
    40.  
    41. protected:
    42.     virtual void resizeEvent( QResizeEvent * );
    43.  
    44. private:
    45. 	QwtPlotGrid *grid;
    46. 	QwtLegend *legend;
    47. 	QwtPlotZoomer *zoomer;
    48. };
    49.  
    50. #endif	// SIGLIBGRAPH_H
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    Qt Code: 
    1. /************************************************************
    2. 	SigLibGraph.cpp
    3. 	AW - 31.03.2012
    4. ************************************************************/
    5.  
    6. #include <QApplication>
    7. #include <QtDebug>
    8. #include <qpainter.h>
    9. #include <qwt_plot.h>
    10. #include <qwt_scale_engine.h>
    11. #include <qwt_symbol.h>
    12. #include <qwt_plot_grid.h>
    13. #include <qwt_plot_curve.h>
    14. #include <qwt_legend.h>
    15. #include <qwt_text.h>
    16. #include <qwt_picker.h>
    17. #include <qwt_picker_machine.h>
    18. #include <qwt_plot_zoomer.h>
    19. #include <qwt_plot_renderer.h>
    20. #include <qwt_event_pattern.h>
    21. #include <qwt_text.h>
    22. #include "SigLibGraph.h"
    23.  
    24.  
    25. Plot2D::Plot2D( QString plotTitle,
    26. 					QString xLabel,
    27. 					QString yLabel,
    28. 					QWidget *parent ): 
    29. 					QwtPlot( parent )
    30. {
    31. 	// plot object
    32. 	setTitle( plotTitle );
    33. 	setCanvasBackground( QColor( Qt::darkBlue ));
    34.  
    35. 	// axis
    36. 	setAxisTitle( QwtPlot::xBottom, xLabel );
    37. 	setAxisTitle( QwtPlot::yLeft, yLabel );
    38.  
    39. 	// grid 
    40. 	QwtPlotGrid* grid = new QwtPlotGrid;
    41. 	grid->enableXMin( true );
    42. 	grid->setMajPen( QPen( Qt::white, 0, Qt::DotLine ));
    43. 	grid->setMinPen( QPen( Qt::gray, 0 , Qt::DotLine ));
    44. 	grid->attach( this );
    45.  
    46. 	// legend
    47. 	QwtLegend* legend = new QwtLegend;
    48. 	insertLegend( legend, QwtPlot::RightLegend );
    49.  
    50. 	//zoomer
    51. 	QwtPlotZoomer* zoomer = new QwtPlotZoomer( QwtPlot::xBottom, 
    52. 															QwtPlot::yLeft, 
    53. 															this->canvas() );
    54. 	zoomer->setRubberBand( QwtPicker::RectRubberBand );
    55. 	zoomer->setRubberBandPen( QColor( Qt::green ));
    56. 	zoomer->setTrackerMode( QwtPicker::ActiveOnly );
    57. 	zoomer->setTrackerPen( QColor( Qt::white ));
    58. 	// RightButton: zoom out by one step
    59. 	zoomer->setMousePattern( QwtEventPattern::MouseSelect3,
    60. 										Qt::RightButton );
    61. 	// Ctrl+RightButton: zoom out to full size
    62. 	zoomer->setMousePattern( QwtEventPattern::MouseSelect2,
    63. 										Qt::RightButton, 
    64. 										Qt::ControlModifier );
    65. 	// handle zoom base
    66. 	connect( zoomer, 
    67. 				SIGNAL( zoomed( QRectF )), 
    68. 				SLOT( autoRescale( QRectF )));
    69.  
    70. 	// resize Widget
    71. 	resize( 600, 400 );
    72.  
    73. 	show();
    74. }
    75.  
    76. void Plot2D::autoRescale( QRectF )
    77. {
    78. 	qDebug("Plot2D::autoRescale called!");
    79. 	if( zoomer->zoomRectIndex() == 0 )				// autorescale only if you are at base... 
    80. 	{	
    81. 		this->setAxisAutoScale( QwtPlot::xBottom );
    82. 		this->setAxisAutoScale( QwtPlot::yLeft );
    83. 		this->updateAxes();
    84. 		zoomer->setZoomBase( false );
    85. 	}
    86. }
    87.  
    88. void Plot2D::attachCurve( 	double *xData,
    89. 									double *yData,
    90. 									uint dataCount, 
    91. 									QString curveLabel,
    92. 									QColor curveColor )
    93. {
    94. 	// define the curve object
    95. 	QwtPlotCurve* curve = new QwtPlotCurve;
    96. 	curve->setSamples( xData, yData, dataCount );
    97. 	curve->setPen( QPen( curveColor ));
    98. 	curve->setRenderHint( QwtPlotItem::RenderAntialiased );
    99. 	curve->setTitle( curveLabel );
    100. 	// qDebug() << "curveLabel.isEmpty = " << curveLabel.isEmpty();
    101. 	if ( curveLabel.isEmpty() )
    102. 		curve->setItemAttribute( QwtPlotItem::Legend, false );
    103. 	else 
    104. 		curve->setLegendAttribute( QwtPlotCurve::LegendShowLine );	
    105. 	curve->attach( this );
    106. }
    107.  
    108. void Plot2D::setXAxisScale( double firstValue, double lastValue )
    109. {
    110. 	setAxisScale( xBottom, firstValue, lastValue );
    111. }
    112.  
    113. void Plot2D::setYAxisScale( double firstValue, double lastValue )
    114. {
    115. 	setAxisScale( yLeft, firstValue, lastValue );
    116. }
    117.  
    118. void Plot2D::setXLogAxis()
    119. {
    120. 	setAxisScaleEngine( QwtPlot::xBottom, new QwtLog10ScaleEngine );
    121. }
    122.  
    123. void Plot2D::setYLogAxis()
    124. {
    125. 	setAxisScaleEngine( QwtPlot::yLeft, new QwtLog10ScaleEngine );
    126. }
    127.  
    128. void Plot2D::setBackgroundColor( QColor backgroundColor )
    129. {
    130. 	setCanvasBackground( backgroundColor );
    131. }
    132.  
    133. void Plot2D::resizeEvent( QResizeEvent *event )
    134. {
    135.     QwtPlot::resizeEvent( event );
    136. }
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  2. 15th April 2012, 17:39 #2
    wysota's Avatar
    wysota
    wysota is offline The "Q"
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    Default Re: Problem with zoomer

    In line #51 of your last snippet of code you are creating a local variable called "zoomer" which shadows the variable you have declared as the class member. Thus you end up initializing the local variable instead of the class member. Same goes with other variables, by the way.
    Your biological and technological distinctiveness will be added to our own. Resistance is futile.

    Please ask Qt related questions on the forum and not using private messages or visitor messages.

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  3. The following user says thank you to wysota for this useful post:

    alainstgt (15th April 2012)
  4. 15th April 2012, 23:38 #3
    alainstgt
    alainstgt is offline Novice
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    Default Re: Problem with zoomer

    thank you for your help, Wysota!
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  5. 18th April 2012, 09:46 #4
    alainstgt
    alainstgt is offline Novice
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    Default Re: Problem with zoomer

    I have been asked which changes I made to resolve the issue.

    In SigLibGraph.cpp, instead of
    Qt Code: 
    1. QwtPlotZoomer* zoomer = new QwtPlotZoomer( QwtPlot::xBottom, QwtPlot::yLeft, this->canvas() );
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    just do
    Qt Code: 
    1. zoomer = new QwtPlotZoomer( QwtPlot::xBottom, QwtPlot::yLeft, this->canvas() );
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    Apply the same procedure to grid and legend!
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