How to write a derived class of QwtSymbol?

[momo]

Hi all,

I meet a problem with QwtSymbol, I want to design some symbols so I have to write a derived class of QwtSymbol,
but It seems like that I need to access the PrivateData of parent class, and the Enumerated type Style of parent class doesn't include the style I designed, how could I write this derived class?

Please excuse me for my poor English, I am not good at it, but I am trying to improve it.

Momo

[Uwe]

You can use symbols types >= QwtSymbol::UserStyle + overloading QwtSymbol::renderSymbols(). But I would expect that the implementation you are looking for is to use one of the symbol types >= QwtSymbol::Path.

Uwe

[momo]

Hi Uwe,
Thank you for your reply. My team use Qwt 6.0.2 to develop so I can not use QwtSymbol::Path.
In my derived class CSymbol I wrote an enum Style that added a TestSymbol after UserStyle, now I meet two questions:
1. How to write CSymbol's Constructors? QwtSymbol's constructors need QwtSymbol::Style in theirs first parameter, but I have to use CSymbol::Style.
2. In QwtSymbol::renderSymbols() (It called drawSymbols() in Qwt6.0.2) it accessed d_data which is private in parent class, and one of the d_data's memeber is QwtSymbol::Style, but I have to use CSymbol::Style. Should I write a new d_data?

Here is Symbol.h's code:

#ifndef SYMBOL_H_
#define SYMBOL_H_
 
#include <qwt/qwt_symbol.h>
 
class CSymbol : public QwtSymbol
{
public:
	 enum Style
    {
        //! No Style. The symbol cannot be drawn.
        NoSymbol = -1,
 
        //! Ellipse or circle
        Ellipse,
 
        //! Rectangle
        Rect,
 
        //!  Diamond
        Diamond,
 
        //! Triangle pointing upwards
        Triangle,
 
        //! Triangle pointing downwards
        DTriangle,
 
        //! Triangle pointing upwards
        UTriangle,
 
        //! Triangle pointing left
        LTriangle,
 
        //! Triangle pointing right
        RTriangle,
 
        //! Cross (+)
        Cross,
 
        //! Diagonal cross (X)
        XCross,
 
        //! Horizontal line
        HLine,
 
        //! Vertical line
        VLine,
 
        //! X combined with +
        Star1,
 
        //! Six-pointed star
        Star2,
 
        //! Hexagon
        Hexagon,
 
        /*!
         Styles >= QwtSymbol::UserSymbol are reserved for derived
         classes of QwtSymbol that overload drawSymbols() with
         additional application specific symbol types.
         */
        UserStyle = 1000,
 
	TestSymbol
    };
 
public:
	// How to write this Constructors?
	CSymbol( Style style = NoSymbol ) : QwtSymbol(style) {};
	CSymbol( Style style, const QBrush &brush, const QPen &pen, const QSize &size )
		: QwtSymbol(style, brush, pen, size) {};
	CSymbol( const CSymbol &symbol ) : QwtSymbol(symbol) {};
	virtual ~CSymbol() {~QwtSymbol(); };
 
protected:
	virtual void drawSymbols( QPainter *,
		const QPointF *, int numPoints ) const;
}; // SYMBOL_H_
#endif

#ifndef SYMBOL_H_
#define SYMBOL_H_

#include <qwt/qwt_symbol.h>

class CSymbol : public QwtSymbol
{
public:
	 enum Style
    {
        //! No Style. The symbol cannot be drawn.
        NoSymbol = -1,

        //! Ellipse or circle
        Ellipse,

        //! Rectangle
        Rect,

        //!  Diamond
        Diamond,

        //! Triangle pointing upwards
        Triangle,

        //! Triangle pointing downwards
        DTriangle,

        //! Triangle pointing upwards
        UTriangle,

        //! Triangle pointing left
        LTriangle,

        //! Triangle pointing right
        RTriangle,

        //! Cross (+)
        Cross,

        //! Diagonal cross (X)
        XCross,

        //! Horizontal line
        HLine,

        //! Vertical line
        VLine,

        //! X combined with +
        Star1,

        //! Six-pointed star
        Star2,

        //! Hexagon
        Hexagon,

        /*!
         Styles >= QwtSymbol::UserSymbol are reserved for derived
         classes of QwtSymbol that overload drawSymbols() with
         additional application specific symbol types.
         */
        UserStyle = 1000,

	TestSymbol
    };

public:
	// How to write this Constructors?
	CSymbol( Style style = NoSymbol ) : QwtSymbol(style) {};
	CSymbol( Style style, const QBrush &brush, const QPen &pen, const QSize &size )
		: QwtSymbol(style, brush, pen, size) {};
	CSymbol( const CSymbol &symbol ) : QwtSymbol(symbol) {};
	virtual ~CSymbol() {~QwtSymbol(); };

protected:
	virtual void drawSymbols( QPainter *,
		const QPointF *, int numPoints ) const;
}; // SYMBOL_H_
#endif

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Here is CSymbol::drawSymbols()'s code:

void CSymbol::drawSymbols( QPainter *painter,
							const QPointF *points, int numPoints ) const
{
	if ( numPoints <= 0 )
		return;
 
	painter->save();
 
	// here is accessing QwtSymbol::d_data
	switch ( d_data->style )
	{
case CSymbol::Ellipse:
	{
		qwtDrawEllipseSymbols( painter, points, numPoints, *this );
		break;
	}
case CSymbol::Rect:
	{
		qwtDrawRectSymbols( painter, points, numPoints, *this );
		break;
	}
	case CSymbol::Diamond:
	{
		qwtDrawDiamondSymbols( painter, points, numPoints, *this );
		break;
	}
	case CSymbol::Cross:
	{
		qwtDrawLineSymbols( painter, Qt::Horizontal | Qt::Vertical,
			points, numPoints, *this );
		break;
	}
	case CSymbol::XCross:
	{
		qwtDrawXCrossSymbols( painter, points, numPoints, *this );
		break;
	}
	case CSymbol::Triangle:
	case CSymbol::UTriangle:
	{
		qwtDrawTriangleSymbols( painter, QwtTriangle::Up,
			points, numPoints, *this );
		break;
	}
	case CSymbol::DTriangle:
	{
		qwtDrawTriangleSymbols( painter, QwtTriangle::Down,
			points, numPoints, *this );
		break;
	}
	case CSymbol::RTriangle:
	{
		qwtDrawTriangleSymbols( painter, QwtTriangle::Right,
			points, numPoints, *this );
		break;
	}
	case CSymbol::LTriangle:
	{
		qwtDrawTriangleSymbols( painter, QwtTriangle::Left,
			points, numPoints, *this );
		break;
	}
	case CSymbol::HLine:
	{
		qwtDrawLineSymbols( painter, Qt::Horizontal,
			points, numPoints, *this );
		break;
	}
	case CSymbol::VLine:
	{
		qwtDrawLineSymbols( painter, Qt::Vertical,
			points, numPoints, *this );
		break;
	}
	case CSymbol::Star1:
	{
		qwtDrawStar1Symbols( painter, points, numPoints, *this );
		break;
	}
	case CSymbol::Star2:
	{
		qwtDrawStar2Symbols( painter, points, numPoints, *this );
		break;
	}
	case CSymbol::Hexagon:
	{
		qwtDrawHexagonSymbols( painter, points, numPoints, *this );
		break;
	}
	case CSymbol::TestSymbol:
	{
		qwtDrawTestSymbols( painter, points, numPoints, *this );
		break;
	}
	default:;
	}
	painter->restore();
}

void CSymbol::drawSymbols( QPainter *painter,
							const QPointF *points, int numPoints ) const
{
	if ( numPoints <= 0 )
		return;

	painter->save();

	// here is accessing QwtSymbol::d_data
	switch ( d_data->style )
	{
case CSymbol::Ellipse:
	{
		qwtDrawEllipseSymbols( painter, points, numPoints, *this );
		break;
	}
case CSymbol::Rect:
	{
		qwtDrawRectSymbols( painter, points, numPoints, *this );
		break;
	}
	case CSymbol::Diamond:
	{
		qwtDrawDiamondSymbols( painter, points, numPoints, *this );
		break;
	}
	case CSymbol::Cross:
	{
		qwtDrawLineSymbols( painter, Qt::Horizontal | Qt::Vertical,
			points, numPoints, *this );
		break;
	}
	case CSymbol::XCross:
	{
		qwtDrawXCrossSymbols( painter, points, numPoints, *this );
		break;
	}
	case CSymbol::Triangle:
	case CSymbol::UTriangle:
	{
		qwtDrawTriangleSymbols( painter, QwtTriangle::Up,
			points, numPoints, *this );
		break;
	}
	case CSymbol::DTriangle:
	{
		qwtDrawTriangleSymbols( painter, QwtTriangle::Down,
			points, numPoints, *this );
		break;
	}
	case CSymbol::RTriangle:
	{
		qwtDrawTriangleSymbols( painter, QwtTriangle::Right,
			points, numPoints, *this );
		break;
	}
	case CSymbol::LTriangle:
	{
		qwtDrawTriangleSymbols( painter, QwtTriangle::Left,
			points, numPoints, *this );
		break;
	}
	case CSymbol::HLine:
	{
		qwtDrawLineSymbols( painter, Qt::Horizontal,
			points, numPoints, *this );
		break;
	}
	case CSymbol::VLine:
	{
		qwtDrawLineSymbols( painter, Qt::Vertical,
			points, numPoints, *this );
		break;
	}
	case CSymbol::Star1:
	{
		qwtDrawStar1Symbols( painter, points, numPoints, *this );
		break;
	}
	case CSymbol::Star2:
	{
		qwtDrawStar2Symbols( painter, points, numPoints, *this );
		break;
	}
	case CSymbol::Hexagon:
	{
		qwtDrawHexagonSymbols( painter, points, numPoints, *this );
		break;
	}
	case CSymbol::TestSymbol:
	{
		qwtDrawTestSymbols( painter, points, numPoints, *this );
		break;
	}
	default:;
	}
	painter->restore();
}

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Momo

[Uwe]

Simply start with your enum ( no need to copy the QwtSymbol symbol types ) from QwtSymbol::UserStyle and use c++ casts. In the end an enum is just a number and it is completely safe to cast between them.

Uwe

[momo]

Problem solved. Thank you Uwe!

Momo