QwtRasterData and values

[jcox23]

[EDIT]:
aaaahh.. I should have wait a little more before posting that...
turns out it's a similar problem as the op had...
x ,y values being asked outside the container...
SORRY....[/EDIT]

Hi,
I'm reviving an old thread... I just stumbled upon this while trying to solve a pb of mine using QwtRasterData...

I have a QMap container filled with data created somewhere else in the program...
the following class is used like this
d_spectrogram->setData(SpectrogramData(&data));

this code:

class SpectrogramData: public QwtRasterData
{
    public:
    SpectrogramData(QMap<int, double*>* points):
        QwtRasterData(QwtDoubleRect(0.0, 0.0, 1999.0, 1999.0))
    { 
        datas = points;
    }
 
    virtual SpectrogramData *copy() const
    {
        SpectrogramData* spec_data = new SpectrogramData(datas);
        return spec_data;       
    }
 
    virtual QwtDoubleInterval range() const
    {
        return QwtDoubleInterval(0.0, 1000.0);
    }
 
    virtual double value(double x, double y) const
    {
 
        int X = qRound(x);
        int Y = qRound(y);
        return (datas->value(X))[Y];
    }
 
    private:
    QMap<int, double*> *datas;
 
};

class SpectrogramData: public QwtRasterData
{
    public:
    SpectrogramData(QMap<int, double*>* points):
        QwtRasterData(QwtDoubleRect(0.0, 0.0, 1999.0, 1999.0))
    { 
        datas = points;
    }

    virtual SpectrogramData *copy() const
    {
        SpectrogramData* spec_data = new SpectrogramData(datas);
        return spec_data;       
    }

    virtual QwtDoubleInterval range() const
    {
        return QwtDoubleInterval(0.0, 1000.0);
    }

    virtual double value(double x, double y) const
    {

        int X = qRound(x);
        int Y = qRound(y);
        return (datas->value(X))[Y];
    }
    
    private:
    QMap<int, double*> *datas;
    
};

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This consistently giving a segentation fault...happening when the object returned by the copy method is used...
Leave alone the fact that I dont understand why 2 SpectrogramData objects are used,

it seems that the copied object will contain a non null pointer to a non-empty container, as its parent...

If somebody can shed some light on the silly mistake I made!

[Uwe]

The map is somewhere allocated in your application code. It's up to the application code to take care of its lifetime. Also check the indices before accessing your map and double arrays - without setting the bounding rect you can be sure to see requests for positions you don't have.

Note, that SpectrogramData::value() is called very often ( for each pixel of your plot canvas: width * height ). So better don't use a QMap. Returning a rasterHint should be useful as well.

Uwe

[jcox23]

The map is somewhere allocated in your application code. It's up to the application code to take care of its lifetime.

Yes it is created outside the code, I cant afford copying it around, it can be big, and there's several of them...RAM usage could quickly explode...

Also check the indices before accessing your map and double arrays - without setting the bounding rect you can be sure to see requests for positions you don't have.

Yes turns out it was just that, a position request was outside the boundaries of my map...

Note, that SpectrogramData::value() is called very often ( for each pixel of your plot canvas: width * height ). So better don't use a QMap. Returning a rasterHint should be useful as well.
Uwe

I know, but QMap is just very convenient in my case, i have series of vectors (double) keyed by integers that are not linearly increasing....
QHash would be probably a bit faster, is that what you were thinking about or even going further than that by using a more low level container... like a long flatten array for example?