QLabel Pixmap doesnt match with true size

[Infestor]

Hi,

I want to implement a minimap into my application and have the following code for that

	layout_ = new QBoxLayout(QBoxLayout::TopToBottom, this);
	p = new QPixmap("minimap.png");
        l = new QLabel();

	l->setPixmap(*p);
	layout_->addWidget(l, 1, Qt::AlignCenter);

Via mousePressEvent i can now click on the minimap and change my position on the real map. However i noticed that the point 0,0 in the minimap widget is not part of the image. (and so are other points likewise). Is there a way to fix this such that the 0,0 coordinate is the top left point of the image?

[SGaist]

Hi,

Can you show what you get ?

[Pl45m4]

@Infestor said in QLabel Pixmap doesnt match with true size:

point 0,0 in the minimap widget is not part of the image.

There might be some margin / border.

Btw: What coordinate system do you use, when you print out the point, where you have clicked?
The result you get could be in parent coordinates.

[Infestor]

@Pl45m4 Yes i think thats the case too. I have a layout that adds the minimap. However i thought that implementing the mousePressEvent in the minimap widget would yield the minimap coordinates and not the parent ones. Is there a way to fix this?

[mrjj]

@Infestor
Hi
Can you show us how you done as mousePress event override directly in the MiniMap
should work and have top,left as 0,0

[Infestor]

Sure, here you go

void MiniMap::mousePressEvent(QMouseEvent* event)
{
	int mouse_x = event->pos().x() ;
	int mouse_y = event->pos().y();

      //...logic


}

Is it needed to pass the event on to the parent?

[mrjj]

@Infestor

Hi
It's often best to call the base class when you override a function but
since QLabel don't use it for any features, it's not needed in this
case. ( but not hurt either)

so if you qDebug()
mouse_x and mouse_y

they are not in local coordinates?

I tested with

class ClickImage : public QLabel
{
    Q_OBJECT
public:
    explicit ClickImage(QWidget *parent = nullptr)
        : QLabel(parent) {}
    ~ClickImage() {}
signals:
    void clicked(int x, int y);
protected:
    void mousePressEvent(QMouseEvent *event) override
    {
        int mx = event->pos().x();
        int my = event->pos().y();
        qDebug() << mx << "-" << my;
        emit clicked(mx, my);
    }
};

and the mx and my are as expected so not sure why it would be for you.

Are you sure you adjusted the logic to now be inside the minimap ?

[Infestor]

Sorry but what do you mean by adjusting the logic? The only thing this class does or add can be seen in my initial post. Does adding stretching/spacing mess with the coordinates? I appreciate your effort though.

[mrjj]

@Infestor
Nope, if the widget is shown(visible) it should always be correct.

By adjusting logic i mean if you fixed the offset before and then move code, then
that part would no longer be needed.

So if you print out your mouse_x and mouse_y what do they show ?

[Infestor]

The top left corner of the image starts at 10, 10. It generally seems like that there is a ~10 pixel wide border around the image. And no the image doesnt have that border so thats not the problem.

[Christian Ehrlicher]

Did you set the label size to the size of the pixmap? I don't see this so the label may be bigger than the pixmap. Also you're leaking the QPixmap instance - no need to create a pointer here.

[mrjj]

Hi
Also notice the layout_ has a margin of 9 pr default.

layout_->setContentsMargins(0,0,0,0); to be sure its not that.

[Infestor]

Edit: @mrjj Thank you so much, that was the issue. How would you know that though...

Also how am i leaking pixmap memory? I free the pixmap in the destructor which isnt shown here.

[mrjj]

@Infestor
Super
well i have had other cases with mysterious gaps and your "~10 pixel wide border " reminded me.

Well then you dont leak it then but you also don't need to as QPixmap is meant to be copied (and its cheap)

QPixmap p("minimap.png");
l->setPixmap(p);

is better as then we cant forget to delete the pixmap and setPixmap copies it anyway.

When ever you need to use * with Qt classes you give to other Qt class, its a sign you shouldn't need to new it.