In below code I'm trying to set scales for X and Y axis. I use setAxisScale but scale doesn't change and I don't see any curves. I must admit Qwt doesn't have user-friendly designed interface.

Qt Code: 
  1. #ifndef PLOT_H
  2. #define PLOT_H
  3.  
  4. #include <qvaluelist.h>
  5.  
  6. #include <qwt_plot.h>
  7. #include <qwt_plot_marker.h>
  8. #include <qwt_plot_curve.h>
  9. #include <qwt_legend.h>
  10. #include <qwt_scale_engine.h>
  11. #include <qwt_data.h>
  12. #include <qwt_text.h>
  13.  
  14. #include <math.h>
  15.  
  16. class Plot : public QwtPlot
  17. {
  18. 	public:
  19. 		Plot()
  20. 		{
  21. 			curves.setAutoDelete(true);
  22. 			X.setAutoDelete(true);
  23. 			Y.setAutoDelete(true);
  24.  
  25. 			setTitle("A Simple QwtPlot Demonstration");
  26. 			insertLegend(new QwtLegend(), QwtPlot::RightLegend);
  27.  
  28. 			// Set axis titles
  29. 			setAxisTitle(xBottom, "x -->");
  30. 			setAxisTitle(yLeft, "y -->");
  31. /*
  32. 			setAxisAutoScale(xBottom);
  33. 			setAxisAutoScale(xTop);
  34. 			setAxisAutoScale(yLeft);
  35. 			setAxisAutoScale(yRight);
  36. */
  37. 			minX = 0.0;
  38. 			maxX = 0.0;
  39. 			minY = 0.0;
  40. 			maxY = 0.0;
  41.  
  42. 			setAxisScaleEngine(xBottom, new QwtLinearScaleEngine());
  43. 			setAxisScaleEngine(yLeft, new QwtLinearScaleEngine());
  44.  
  45.     			// Insert markers
  46.  
  47. 			//  ...a horizontal line at y = 0...
  48. /*
  49. 			QwtPlotMarker *mY = new QwtPlotMarker();
  50. 			mY->setLabel(QString::fromLatin1("y = 0"));
  51. 			mY->setLabelAlignment(Qt::AlignRight|Qt::AlignTop);
  52. 			mY->setLineStyle(QwtPlotMarker::HLine);
  53. 			mY->setYValue(0.0);
  54. 			mY->attach(this);
  55. */
  56.  
  57.     			//  ...a vertical line at x = 2 * pi
  58. /*
  59. 			QwtPlotMarker *mX = new QwtPlotMarker();
  60. 			mX->setLabel(QString::fromLatin1("x = 2 pi"));
  61. 			mX->setLabelAlignment(Qt::AlignRight|Qt::AlignTop);
  62. 			mX->setLineStyle(QwtPlotMarker::VLine);
  63. 			mX->setXValue(1000.0);
  64. 			mX->attach(this);
  65. */
  66. 		}
  67.  
  68. 		~Plot()
  69. 		{
  70. 			curves.clear();
  71. 			X.clear();
  72. 			Y.clear();
  73. 		}
  74.  
  75. 		void addCurve(QValueList<double> & list)
  76. 		{
  77. 			double * x = new double[list.count()];
  78. 			double * y = new double[list.count()];
  79.  
  80. 			for (unsigned int i = 0 ; i < list.count() ; i++)
  81. 			{
  82. 				x[i] = i;
  83. 				y[i] = list[i];
  84. 			}
  85.  
  86. 			X.append(x);
  87. 			Y.append(y);
  88.  
  90.  
  91. 			c->setRawData(x, y, list.count());
  92. 			c->attach(this);
  93.  
  94. 			if (c->minXValue() < minX)
  95. 				minX = c->minXValue();
  96.  
  97. 			if (c->maxXValue() > maxX)
  98. 				maxX = c->maxXValue();
  99.  
  100. 			if (c->minYValue() < minY)
  101. 				minY = c->minYValue();
  102.  
  103. 			if (c->maxYValue() > maxY)
  104. 				maxY = c->maxYValue();
  105.  
  106. 			setAxisScale(xBottom, minX, maxX);
  107. 			setAxisScale(yLeft, minY, maxY);
  108.  
  109. 			curves.append(c);
  110. 		}
  111.  
  112. 	private:
  113. 		QPtrList<QwtPlotCurve> curves;
  114. 		QPtrList<double> X;
  115. 		QPtrList<double> Y;
  116. 		double minX;
  117. 		double maxX;
  118. 		double minY;
  119. 		double maxY;
  120. };
  121.  
  122. #endif
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