CODEWITHSUNDEEP
c++qt
jdepypere
jdepypere

Reputation: 3553

Qt Update Pixmap of QGraphicsPixmapItem

I am using the QGraphicsPixmapItem to show an image on the display. Now, I want to be able to update this image on the fly, but I seem to be running into some issues.

This is the header file:

class Enemy_View : public QGraphicsPixmapItem
{
public:
    Enemy_View(QGraphicsScene &myScene);
    void defeat();
private:
    QGraphicsScene &scene;
    QPixmap image;
}

And here is the cpp file

Enemy_View::Enemy_View(QGraphicsScene &myScene):
    image{":/images/alive.png"}, scene(myScene)
{
    QGraphicsPixmapItem *enemyImage = scene.addPixmap(image.scaledToWidth(20));
    enemyImage->setPos(20, 20);
    this->defeat();
}

void Enemy_View::defeat(void)
{
    image.load(":/images/dead.png");
    this->setPixmap(image);
    this->update();
}

SO the idea is that I want to be able to call the defeat method on my object, that then edits some attributes and eventually changes the image. However, what I am doing now does not work. The alive.png image does display, but does not get updated to the dead.png one.

Update 1

As mentioned by Marek R I appear to be replicating a lot of built-in functionality. I tried to clean this up but now nothing is showing up on the scene anymore.

.h file

class Enemy_View : public QGraphicsPixmapItem
{
public:
    Enemy_View(QGraphicsScene &myScene);
    void defeat();

private:
    QGraphicsScene &scene;
    /* Extra vars */
};

.cpp file

Enemy_View::Enemy_View(QGraphicsScene &myScene):
    scene(myScene)
{
    /* This part would seem ideal but doesn't work */
    this->setPixmap(QPixmap(":/images/alive.png").scaledToWidth(10));
    this->setPos(10, 10);
    scene.addItem(this);

    /* This part does render the images */
    auto *thisEl = scene.addPixmap(QPixmap(":/images/Jackskellington.png").scaledToWidth(10));
    thisEl->setPos(10, 10);
    scene.addItem(this);

    this->defeat();
}

void Enemy_View::defeat(void)
{
    this->setPixmap(QPixmap(":/images/dead.png"));
}

So I removed the QPixmap, but I'm not sure whether I can remove the QGraphicsScene. In my cpp-file you can see I have two versions of the constructor now. The first part, using the this seems like an ideal solution, but does not display the image on the screen (even though it does compile without errors). The second version with thisEl does render it. What am I doing wrong with the first version?

Upvotes: 4

Views: 6902

Answers (1)

Marek R
Marek R

Reputation: 37697

Why FGS you are subclassing QGraphicsPixmapItem? QGraphicsPixmapItem has all functionality you need. And those new fields you have added does nothing, they only try replicate functionality which is already there (but with this implementation it does nothing).

This suppose to be something like that:

QPixmp image(":/images/alive.png");
QGraphicsPixmapItem *enemyItem = scene.addPixmap(image.scaledToWidth(20));
enemyItem->setPos(20, 20);

// and after something dies
QPixmap dieImage(":/images/dead.png");
enemyItem->setPixmap(dieImage);

Upvotes: 5

Related Questions