How to display image on specific coordinates in Qt? - c++

Question

I have this dialog window class in Qt:
class Board : public QDialog
{
Q_OBJECT
public:
explicit Board(QWidget *parent = 0);
~Board();
private:
Ui::Board *ui;
void mousePressEvent(QMouseEvent *mouseEvent);
};
I want to dislay a png image on user given coordinates in function mousePressEvent, which is called every time user clicks somewhere on the dialog window. So I need something like displayImage("path/to/image.png", coordX, coordY);. How can I do it?
The new code:
class Board : public QDialog
{
public:
Board(QWidget *parent = 0) :
QDialog(parent),
ui(new Ui::Board),
view(&scene)
{
// Set background image
/**************/
ui->setupUi(this);
QPixmap pix("path/background.png");
ui->label_board->setPixmap(pix);
/**************/
/ Set layout for displaying other images on the background
QVBoxLayout *layout = new QVBoxLayout(this);
layout->addWidget(&view);
//or set the layout and the view in the designer if using Qt Creator
}
protected:
virtual void mousePressEvent(QMouseEvent *mouseEvent) override
{
QGraphicsPixmapItem *item = new QGraphicsPixmapItem(QPixmap("path/to/image.png"));
scene.addItem(item);
item->setPos(coordX, coordY);
}
private:
Ui::Board *ui;
QGraphicsScene scene;
QGraphicsView view;
};
The label_board is a label 500x500 set to some position with Qt Designer.

Answer 1

You will need to use QGraphicsView (docs) and QGraphicsScene (docs):
class Board : public QDialog
{
public:
Board(QWidget *parent = 0) :
QDialog(parent),
ui(new Ui::Board),
view(&scene)
{
QVBoxLayout *layout = new QVBoxLayout(this);
layout->addWidget(&view);
//or set the layout and the view in the designer if using Qt Creator
//EDIT: add background like this first
QGraphicsPixmapItem *background = QGraphicsPixmapItem(QPixmap("path/to/background.png"));
scene.addItem(background);
background.setPos(0, 0); //position it to cover all the scene so at 0,0 which is the origin point
background.setScale(2.0); //scale the image to the scene rectangle to fill it
background.setZValue(-0.1); //to ensure it is always at the back
}
protected:
virtual void mousePressEvent(QMouseEvent *mouseEvent) override
{
QGraphicsPixmapItem *item = new QGraphicsPixmapItem(QPixmap("path/to/image.png"));
scene.addItem(item);
item->setPos(coordX, coordY);
}
private:
Ui::Board *ui;
QGraphicsScene scene;
QGraphicsView view;
};
And that is pretty much it. Also note that the position is that of upper left corner of the item (image). If you would want to center it you would need to adjust the position based on the proportions of the item (image).