[PyKDE] pointer to underlying C++ object?

Phil Thompson phil at river-bank.demon.co.uk
Wed Sep 4 09:37:00 BST 2002

Mark Phillips wrote:

>>Using SIP to create the wrapper for foo() should allow you to do exactly
>>want to want. You shouldn't have got "similar problems".
> Oops.  Sorry for my confusion.  I actually did have some problems
> getting it to work with sip, but I guess they weren't so "similar".
> Anyway, inspired by your encouragement I've spent a lot more time with
> sip now and have made some progress.  I discovered '%Import qtmod.sip'
> which seems to be what's needed to get sip to know about existing Qt
> classes, and my sip function wrapper now correctly builds and runs.
> However, it turns out that what I'm actually trying to do is more
> complicated, and I'm still stuck on something.  The purpose of the
> function I'm wrapping is to move pixels from a gdImage object (from
> the 'gd' graphics library) into a QImage object so that it can be
> rendered in a Qt application window:
>    void gdImageToQImage(QImage *im, gdImage *gd)
> I've written this function in C++, tested it from a C++ program, and
> it works fine.  I'm trying to wrap it so that I can write the
> application in python with PyQt, rather than in C++.
> Now that I understand how to deal with the QImage* argument, I've moved
> on to the gdImage* argument, which is more challenging.  In python,
> the gdImage object that I want to pass to this function corresponds to
> a swig-wrapped object, rather than a sip-wrapped one.  I guess I can't
> teach sip about gdImage by '%Import'ing its sip module, because there
> isn't one.  Is there some way I can tell sip enough about an object
> wrapped by swig to allow it to correctly deal with a pointer to that
> object?  I tried simply putting
>    class gdImage {
>    public:
>      gdImage();
>    };
> in my sip file, but I still get
>    TypeError: Argument 2 of gdImageToQImage() has an invalid type
> at runtime.
> Or, perhaps this isn't a sip issue. Perhaps there's some way I can
> tell python to pass a pointer to the underlying C++ object to my
> function, and just declare the function to take a void * argument.
> But as I said, I'm new to much of this, and I haven't yet figured out
> if that's possible, or how.
> Maybe there's even a more straightforward way to get pixels from a
> gdImage object into something that I can render in Qt, eliminating the
> need for a custom function altogether???
> Thanks in advance for any help!

What sort of Python object is being passed as the gdImage argument? In 
other words, how does SWIG wrap it?

The best approach is to define gdImage as a %MappedType which allows you 
to define C++ convertors to and from the SWIG wrapped object to a SIP 
wrapped object - but you will need to know how to extract the underlying 
C++ pointer from the SWIG wrapped object.


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