QTimer won't advance screen - c++

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.