GameDev on Qt - Tutorial 5. The explosion of bullets using sprite images

sprite sheet, sprite, GameDev, QPixmap, Спрайт, explosion. взрыв, Qt, Bullet

In previous articles we have learned to draw a sprite image and apply it to Qt via QPixmap so we turned animated explosion. And now we need to put this very explosion at precisely the place where the bullet hits. That is, the bullet will explode.

For the implementation of this ideas will add class sprite from the past lessons, and modify it. The fact is that the sprite object is a class inherited from QGraphicsItem , and therefore a bullet when confronted with the explosion of another bullet will behave as well as in a collision with an obstacle or a target. Therefore it is necessary to do so to ignore the bullets from the other explosions and bullets flying through.

Project structure

The project is subject to modification in the sense that a new class is added to the following files:

• sprite.h
• sprite.cpp

This class will be called animated sprite explosion, after which this frame object will be removed from the graphic scene.

sprite.h

Compared with the code from lesson on connecting animated sprites in Qt in this class must override the virtual function type(), and replace the type identifier of our graphic object to distinguish it from the other types of identifiers of graphic objects. For example Type will be equal UserType + 1 instead UserType .

#ifndef SPRITE_H
#define SPRITE_H

#include <QObject>
#include <QGraphicsItem>
#include <QTimer>
#include <QPixmap>
#include <QPainter>

class Sprite : public QObject, public QGraphicsItem
{
    Q_OBJECT
public:
    explicit Sprite(QPointF point, QObject *parent = 0);

    /* Override the type of graphic object explosion that bullet could ignore this object
     * */
    enum { Type = UserType + 1 };

    // Also override function for the object type
    int type() const;

signals:

public slots:

private slots:
    void nextFrame();   /// Slot for turning frames

private:
    void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget);
    QRectF boundingRect() const;

private:
    QTimer *timer;  /// The timer for the animation of the explosion
    QPixmap *spriteImage;   /// QPixmap for the sprite with the explosion
    int currentFrame;   /// Coordinate of the current frame in sprite
};

#endif // SPRITE_H

sprite.cpp

The source code will also attend the change. In addition, we are redefining the type() function. We also makes changes to the slot to switch sprite frames. Initially looping animation has been set in the code. In this case, at the expiration of all of the frames need to be deleted from a graphics scene object that is implemented in this slot.

Also there is a small change in the Sprite class constructor. In it added an argument that specifies the position of an explosion on the graphic scene. That is, the bullet will pass in this class is the place of the explosion.

#include "sprite.h"

Sprite::Sprite(QPointF point, QObject *parent) :
    QObject(parent), QGraphicsItem()
{
    this->setPos(point);    // Set the position of the blast
    currentFrame = 0;       /// X coordinate of the beginning of the explosion of bullets
    spriteImage = new QPixmap(":/sprites/sprite_sheet.png");

    timer = new QTimer();   /// Initialize timer explosion animation
    connect(timer, &QTimer::timeout, this, &Sprite::nextFrame);
    timer->start(25);   /// We start the timer at 25 milliseconds
}

QRectF Sprite::boundingRect() const
{
    return QRectF(-10,-10,20,20);
}

void Sprite::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
    // Draw one of the frames of the explosion
    painter->drawPixmap(-10,-10, *spriteImage, currentFrame, 0, 20,20);
    Q_UNUSED(option);
    Q_UNUSED(widget);
}

void Sprite::nextFrame()
{
    currentFrame += 20; // We change the X coordinate to select the next frame
    if (currentFrame >= 300 ) {
        this->deleteLater();    // If shots are over, then remove the explosion object
    } else {
        this->update(-10,-10,20,20);    
    }
}

int Sprite::type() const {
    return Type;
}

bullet.h

In this file, only connect the Sprite class.

bullet.cpp

But in the Bullet class we change a few lines of code. It will be necessary to find in slotTimerBullet() function section of code that is responsible for checking on the fact of collision with other objects.

This part is a foreach loop. In it we add a check for a collision with another explosion, and if such a collision does not exist, but there is a clash with any other object, you create an explosion and destroy the bullet.

The nuance of this code is that we do not object to qgraphicsitem_cast sprite class. Since the creation of this object is assigned (UserType + 1) , and QGraphicsItem has a function type(), then it is enough to determine what object hit a bullet.

void Bullet::slotTimerBullet()
{
    setPos(mapToParent(0, -10));

    QList<QGraphicsItem *> foundItems = scene()->items(QPolygonF()
                                                           << mapToScene(0, 0)
                                                           << mapToScene(-1, -1)
                                                           << mapToScene(1, -1));

    foreach (QGraphicsItem *item, foundItems) {
        /* Add to the test more and explosions themselves 
         * to ignore their bullets and exploding hitting in explosion from another bullet
         * */
        if (item == this || item == hero || item->type() == (UserType + 1))
            continue;
        // When you hit the target or wall, causes an explosion
        scene()->addItem(new Sprite(this->pos()));
        callbackFunc(item);     // Вызываем CallBack функцию
        this->deleteLater();    // Уничтожаем пулю
    }

    if(this->x() < 0){
        this->deleteLater();
    }
    if(this->x() > 500){
        this->deleteLater();
    }

    if(this->y() < 0){
        this->deleteLater();
    }
    if(this->y() > 500){
        this->deleteLater();
    }
}

Result

As a result of the work done in the field impact of the bullet will be formed bursts, as shown in the figure.

Link to project downloading: targetmotion.zip

Video