Jarrod A. February 2016

How to exit a "game" in Qt when health is 0

I'm quite new to Qt, but I got into it to start experimenting with making 2D games. I've got a extremely rough and simple game started, but I have an issue. Whenever the health gets to 0, the game doesn't end. I just want to know how to end the game and where to put this exit command before making a "Game Over" screen. My code is below, and from what I can grasp, I assume the QApplication::quit() goes in the Game.cpp file. Doing this by taking the health integer from Health.cpp and Health.h and putting it in Game.cpp. Any help is appreciated. Here is the code I feel the answers lie in, if more info is needed, ask.

Game.h

#ifndef GAME_H
#define GAME_H

#include <QGraphicsView>
#include <QWidget>
#include <QGraphicsScene>
#include "Player.h"
#include "Score.h"
#include "Health.h"
#include "Level.h"
#include "Main.h"

class Game: public QGraphicsView{
public:
    Game(QWidget * parent=0);

    QGraphicsScene * scene;
    Player * player;
    Score * score;
    Health * health;
    Level * level;
    Main * close;
    int end();
};

#endif // GAME_H

Game.cpp

#include "Game.h" 
#include <QTimer>
#include <QGraphicsTextItem>
#include <QFont>
#include "Enemy.h"
#include <QMediaPlayer>
#include <QBrush>
#include <QImage>
#include <QApplication>

Game::Game(QWidget *parent){
    // create the scene
    scene = new QGraphicsScene();
    scene->setSceneRect(0,0,800,600); // make the scene 800x600        instead of infinity by infinity (default)
    setBackgroundBrush(QBrush(QImage(":/images/bg.png")));

    // make the newly created scene the scene to visualize (since Game is a QGraphicsView Widget,
    // it can be used to visualize scenes)
    setScene(scene);
    setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
    setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
    setFixedSize(800,600);

    // create the pl        

Answers


jpo38 February 2016

Your end() function is never called.

The best way to achieve what you want to is to use Qt's signal/slot mechanism. It amkes it easy to connect an event (signal) to an action (slot):

  • Add Q_OBJECT macro to Health and Game classes and make sure your compilation environment moc's the two header files
  • Declare in Health a signal named dead()
  • Emit the signal from Health::decrease()
  • Make Game::end() be a slot and be void
  • Connect Health::dead() to Game::end()

Then, Game::end() will be called as soon as Health reaches zero.

class Health: public QGraphicsTextItem 
{
    Q_OBJECT
public:
    Health(QGraphicsItem * parent=0);
    void decrease();
    int getHealth();
signals:
    void dead();
private:
    int health;
};

...

class Game: public QGraphicsView{
    Q_OBJECT
public:
    ...

public slots:
    void end();
};

...

void Health::decrease(){
    health--;
    setPlainText(QString("Health: ") + QString::number(health));
    if ( health == 0 )
        emit dead();
}

...

Game::Game(QWidget *parent){

    ...

    connect( health, SIGNAL(dead()), this, SLOT(end()) );

}

...

void Game::end(){
    // no need to test health anymore, as signal is emited when health is zero
    // do some extra stuff before exiting
    QApplication::quit();
}

If end() only calls QApplication::quit(), you can remove it and diectly connect the signal to QApplication::quit(), like that:

connect( health, SIGNAL(dead()), qApp, SLOT(quit()) );

Also note that you were testing health == 0


phyatt February 2016

In Health::decrease emit a signal or put the logic for it in where the "player is shot" area. But to do that, you to Health or the class with the logic to be a QObject so that it gets the signals and slots in the header. EDIT QGraphicsTextItem is already a QObject. See comments.

Connect the signal to the view's close() right after the Health class or Player class is instantiated.

http://doc.qt.io/qt-5/signalsandslots.html

Hope that helps.

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Asked in February 2016
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