Problem with item positioning

robinfriedli

Hi.

I'm trying to write a simple Snake game with Qt but I have issues with the positioning of the fruit. When the Snake eats the fruit (meaning that if the SnakeHead collides with the fruit) the Fruit should respawn in a random location on the screen.

For that, I use the height and width of the QGraphicsView. As long as I don't resize the window this works fine, but as soon as I do the Fruit will eventually spawn outside of the visible view.

I did some debugging and found that the coordinates are fine. E.g. when I enter fullscreen mode, the QGraphicsView size is 1440x900, as expected on my MacBook Pro, since it has a 1440x900 system resolution despite the 2880x1800 display resolution.

But when the Fruit spawns at, for example, width=1237, height=626, it is not visible. Only when I scale the screen to 1920x1200 I can see it to the very right.

This is how I place the Fruit:

void Game::spawnFruit(){
    int width = rand() % (QGraphicsView::width() - 100);
    int height = rand() % (QGraphicsView::height() - 100);
    f1->setPos(width, height);

    QList<QGraphicsItem*> cItems = scene->collidingItems(f1);
    if(!cItems.empty()) {
        spawnFruit();
    }
}

Again, this only happens when enlarging the window, it works fine if I make it smaller or launch it at full resolution. It probably has something to do with this:

Game::Game(QWidget *parent): QGraphicsView(parent){
    scene = new QGraphicsScene(0,0,800,600);
    setScene(scene);
}

So basically, as soon as the window / QGraphicsView becomes bigger than the QGraphicsScene this problem occurs. If it's smaller, then the window becomes scrollable but the Fruit always spawns within the size of the window. Is there a way to make this responsive?

I'm using Qt Creator 4.5.0 based on Qt 5.10.0.

Thanks in advance.

Asperamanca

When you place fruit, you do that within the GraphicsScene. So it's the size of the GraphicsScene that matters, not the size of the GraphicsView.
QGraphicsScene::sceneRect() might be what you need.