QTimer won't advance screen

Question

I create my scene in my dialog.cpp and draw some QGraphicsItem's in my scene.cpp. When I add my QTimer to my dialog.cpp it makes whenever I move the cursor over the scene to crash.

dialog.cpp

#include "dialog.h"
#include "scene.h"
#include "ui_dialog.h"
#include "instructions.h"
#include "settings.h"
#include "highscore.h"

Dialog::Dialog(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::Dialog)
{
    ui->setupUi(this);

    // Create and configure scene
     scene = new Scene;
     scene->setBackgroundBrush(Qt::black);
     scene->setItemIndexMethod(QGraphicsScene::NoIndex);
     ui->graphicsView->setScene(scene);
     scene->setSceneRect(-200, -150, 400, 300);
     ui->graphicsView->setMouseTracking(true);

     QPixmap tankbase1(":/images/tankbase.jpg");
     ui->tankbaseplay1->setPixmap(tankbase1);

//\/\/\/This is my problem. And not sure why\/\/\/\/\/\/
//     timer = new QTimer(this);
//     QObject::connect(timer, SIGNAL(timeout()), scene, SLOT(advance()));
//     timer->start(10);

}

Dialog::~Dialog()
{
    delete ui;
}

//void Dialog::shoot()
//{

//}


void Dialog::on_startButton_clicked()
{
    ui->settingsButton->hide();
    ui->titlescreen->hide();
    ui->highscoreButton->hide();
    ui->instructionButton->hide();
    ui->startButton->hide();

    QGraphicsTextItem *FirstP;
    QString P1 = "Player1";
    FirstP = scene->addText(P1);
    FirstP->setFont(QFont("Nimbus Mono L", 12,QFont::Bold));
    FirstP->setDefaultTextColor(Qt::white);
    FirstP->setPos(-300, -220);


    QGraphicsTextItem *SecondP;
    QString P2 = "Player2";
    SecondP = scene->addText(P2);
    SecondP->setFont(QFont("Nimbus Mono L", 12,QFont::Bold));
    SecondP->setDefaultTextColor(Qt::white);
    SecondP->setPos(230, -220);
}

void Dialog::on_instructionButton_clicked()
{
    Instructions intDialog;
    intDialog.setModal(true);
    intDialog.exec();
}

void Dialog::on_settingsButton_clicked()
{
    settings intDialog;
    intDialog.setModal(true);
    intDialog.exec();
}


void Dialog::on_highscoreButton_clicked()
{
    highscore intDialog;
    intDialog.setModal(true);
    intDialog.exec();
}

scene.cpp

#include "scene.h"
#include <QGraphicsEllipseItem>
#include <QGraphicsLineItem>
#include <QGraphicsSceneMouseEvent>
#include <QTimer>
#include "qmath.h"
#include <math.h>




class GraphicsCircle : public QGraphicsEllipseItem
// class for the fire bullets
{
public:
    GraphicsCircle(qreal dirx, qreal diry)
        : m_Speed(3)
        , m_DirX(dirx)
        , m_DirY(diry)
    {
        setRect(-3.0,-3.0,8.0,8.0);
        setPos(-195, 130);
        QRadialGradient rGrad( 0.0, 0.0, 20.0, 0.0, 0.0);
        rGrad.setColorAt(0.0, QColor(255,255,255));
        rGrad.setColorAt(0.7, QColor(255,255,225));
        rGrad.setColorAt(1.0, QColor(255,0,0,0));
        setBrush(QBrush(rGrad) );
        setPen(QPen(Qt::NoPen));
    }

    virtual ~GraphicsCircle() {}

    void advance(int phase)
    {
        if(!phase) return;
        setPos(x()+m_Speed*m_DirX, y()+m_Speed*m_DirY);
    }

private:
    qreal m_Speed;
    qreal m_DirX;
    qreal m_DirY;
};

Scene::Scene() : QGraphicsScene()
{
    // added the lines below to setup an item, pointing in the positive x direction
    int x1 = 0;
    int y1 = 0;
    cannon = new QGraphicsLineItem(x1, y1, x1 + 50, y1);
    cannon->setPen(QPen(Qt::white, 6));
    this->addItem(cannon);
    cannon->setPos(-195, 130);

    //Create bullets
    m_FireTimer= new QTimer();
    QObject::connect(m_FireTimer, SIGNAL(timeout()), this, SLOT(fire()));
}

void Scene::mousePressEvent(QGraphicsSceneMouseEvent *e)
{
    m_FireTarget = e->scenePos();
    m_FireTimer->start();
    QGraphicsScene::mousePressEvent(e);
}

void Scene::mouseMoveEvent(QGraphicsSceneMouseEvent *e)
{
//    emit mouseMoving(e->scenePos());
//    FirstPlayer->setPos(e->scenePos());

//    qAtan2(cannon->pos(), e->scenePos());

    m_FireTarget = e->scenePos();
    QGraphicsScene::mouseMoveEvent(e);

    QLineF arm(cannon->pos(), e->scenePos());
    cannon->setRotation(360 - arm.angle());


}

void Scene::mouseReleaseEvent ( QGraphicsSceneMouseEvent * e )
{
    m_FireTimer->stop();
    QGraphicsScene::mouseReleaseEvent(e);
}

void Scene::fire()
// creates a fire bullet
// the bullet will move in the direction of the mouse cursor
// the trajectory is sligthly perturbated by a random small angle
{
    qreal dirx = m_FireTarget.x()-195;
    qreal diry = m_FireTarget.y()-195;

    qreal length = sqrt(dirx*dirx+diry*diry);
    if (length!=0)
    {
        // normalized direction vector
        qreal invLength= 1.0/length;
        dirx *= invLength;
        diry *= invLength;

        // creating an angle perturbation of +/- 3°
        qreal alphaPerturbation = static_cast<qreal>(qrand()%6-3) * M_PI / 180.0;
        qreal xPerturbation = cos(alphaPerturbation);
        qreal yPerturbation = sin(alphaPerturbation);
        dirx = dirx*xPerturbation - diry*yPerturbation;            
        diry = diry*xPerturbation + dirx*yPerturbation;

        GraphicsCircle * circle = new GraphicsCircle(dirx, diry);
        addItem(circle);

    }
}

void Scene::advance()
{
   // first remove the pellet out of the sceneRect
    for (int i=0; i<items().count(); ++i)
    {
        QGraphicsItem * item = items().at(i);
        qreal x= item->x();
        qreal y= item->y();
        qreal sx=sceneRect().width();
        qreal sy= sceneRect().height();
        if ( (x < 0.0) || (y < 0.0) || (x > sx) || (y > sy))
        {
            removeItem(item);
            delete item;
        }
    }
    QGraphicsScene::advance();
}

When I run the code without the QTimer code in dialog.cpp it runs and my QGraphicsItems are displayed and move accordingly. When I add the QTimer the QGraphicsItem disappears. Completely lost to what the issue is.

Also I have taken the scene code and ran it separately and it works. The only difference is the scene and QTimer is created in main.cpp.

Help greatly needed!!!!!

Answer 1

You are iterating through a list of items while you are deleting items in the list. That sounds like trouble.

http://qt-project.org/doc/qt-5/qrect.html#intersects

http://qt-project.org/doc/qt-5/qgraphicsitem.html#boundingRect

http://qt-project.org/doc/qt-5/qrectf.html#contains

I think this might be a little cleaner in your advance() function.

QList <QGraphicsItem *> itemsToRemove;
foreach( QGraphicsItem * item, this->items() )
{
    if( !this->sceneRect().intersects(item->boundingRect()) )
    {
        // The item is no longer in the scene rect, get ready to delete it
        itemsToRemove.append(item);
    }
}

foreach( QGraphicsItem * item, itemsToRemove )
{
    this->removeItem(item);
    delete(item);
}

Also reading the description of QGraphicsScene,

http://qt-project.org/doc/qt-5/qgraphicsscene.html#details

there a number of helper methods that can make finding items in an area or one item colliding with another, much easier.

Hope that helps.