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List:       kde-games-devel
Subject:    [Kde-games-devel] Re: QCanvasSprite + QObject
From:       Andreas Beckermann <b_mann () gmx ! de>
Date:       2001-12-12 20:43:29
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On Wednesday 12 December 2001 20:08, Johnny Andersson wrote:
> Hi. 

Hi

> Is it possible to inherit from both QCanvasSprite and QObject at the
> same time? 

Yes, this is possible - at least IIRC. Boson did this once.

> My program doesn't compile when I do. I've written my own sprite

Why? Can you post the error message=

> class, derived from QObject. I started having trouble when I wanted to use
> collision detection; to use RTTI, I have to derive from QCanvasItem.
>
> As a temporary solution, I created a small class derived form QCanvasSprite
> with the rtti-stuff. This class contains a pointer to my "real" sprite
> object, so that I can find it when Qt reports a collision. An ugly hack.

Well, my test code compiles:

Header:
#include <qobject.h>
#include <qcanvas.h>
class A : public QObject, QCanvasSprite
{
public:
        A() : QObject(0), QCanvasSprite(0,0) { }
        ~A() { }
};

This doesn't do anything useful though. You'll also need to add a rtti() to be 
able to use this at all. But it compiles here.

> Is it just me, or does the QCanvas extension not feel as polished as the
> rest of Qt? While very useful, there are some things that I've had to
> re-design in my program to work around. For example, QCanvasPixmapArray has
> a method setImage(...) to set a specific image in the list, and if needed,
> it extends the list. But I can't create an empty QCanvasPixmapArray and
> then add items to it using setImage, I have to create a dummy array first
> *or* create an empty QCanvasPixmapArray and then call readPixmaps (which if
> of course only relevant if you have the graphics in a file, and not
> generate them yourself).

WHat about this:
 QValueList<QPixmap> pixmapList;
 for(int i = 0; i < pixmaps; i++) {
    QPixmap p = loadPixmap(i);
    pixmapList.push_back(p); // aka append()
 } 
 QCanvasPixmapArray* pixmapArray = new QCanvasPixmapArray(pixmapList);
 if (!pixmapArray->isValid()) {
        return false;
 }
 // ...

This pixmapArray can now be used by you. This is the way we do it in boson - 
the pixmapArray is stored as a pointer so that we can use it for all units of 
this type and don't have to reload it again. Remember to delete the pointer.

CU
Andi
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