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.