Program doesn't draw anything, why?
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Hi all,
I'm programming a a kind of "virtual tennis" game, but when I run it there isn't anything but the grey background. Can you please help understand why?objects.cpp
@#include "objects.h"
Objects::Objects(QWidget *parent) :
QWidget(parent)
{
setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Expanding);
//angoli campo da gioco
Border[0].setY(-height()/2);
Border[0].setX(-width()/2);
Border[1].setY(-height()/2);
Border[1].setX(+width()/2);
Border[2].setY(+height()/2);
Border[2].setX(+width()/2);
Border[3].setY(+height()/2);
Border[3].setX(-width()/2);//dimensioni oggetti WidthPad=13; HeightPad=30; sizeBall=10; //coordinate Pad1 Pad1.setX(-width()+WidthPad); Pad1.setY(-height()/2+HeightPad); //coordinate Pad2 Pad2.setX(width()-WidthPad); Pad2.setY(+height()/2-HeightPad); //coordinate pallina Ball.setX(width()/2); Ball.setY(0);}
QPolygon Objects::BuildRectangle(QPoint location, int Large, int Tall){
QPolygon Rectangle;
QPoint TopRight, BottomRight, BottomLeft;
TopRight.setX(location.x()+Large);
TopRight.setY(location.y());
BottomRight.setX(TopRight.x());
BottomRight.setY(TopRight.y()-Tall);
BottomLeft.setX(location.x());
BottomLeft.setY(BottomRight.y());
Rectangle << location;
Rectangle << TopRight;
Rectangle << BottomRight;
Rectangle << BottomLeft;
return Rectangle;
}void Objects::SetAliasing(bool antialiasing){
this->antialiased = antialiasing;
update();
}void Objects::PaintObjects(QPaintEvent *){
QPainter PaintIt(this);
QPainter PaintThem(this);
QPolygon BorderLine, Plat1, Plat2;//Creazione oggetto grafico per coordinate del confine di giuoco BorderLine << Border[0]; BorderLine << Border[1]; BorderLine << Border[2]; BorderLine << Border[3]; //???????????????????????????? PaintIt.setRenderHint(QPainter::Antialiasing,antialiased); PaintThem.setRenderHint(QPainter::Antialiasing,antialiased); //Creazione oggetti grafici Pad di giuoco Plat1 = BuildRectangle(Pad1,WidthPad,HeightPad); Plat2 = BuildRectangle(Pad2,WidthPad,HeightPad); //Setting di disegno PaintIt.setPen(Qt::black); PaintThem.setPen((Qt::black)); PaintThem.setBrush(Qt::black); //Translazione PaintIt.translate(width(), height()); PaintThem.translate(width(), height()); //Muciaccia PaintIt.drawPolygon(BorderLine); PaintThem.drawPolygon(Plat1); PaintThem.drawPolygon(Plat2); PaintThem.drawEllipse(Ball,sizeBall,sizeBall);}
@virtualtennis.cpp
@#include "virtualtennis.h"
VirtualTennis::VirtualTennis(){
//vettori di spostamento della pallina;
VectorX=5;
VectorY=3;//Oggetti del giuoco mambo=new Objects; //Creazione e settaggio del layout QGridLayout *Layout = new QGridLayout; Layout->addWidget(mambo); setLayout(Layout); setWindowTitle(tr("VIRTUAL TENNIS SINGLE PLAYER")); //Creazione del timer; QTimer *Clock = new QTimer(this); Clock->start(500); connect(Clock, SIGNAL(timeout()),this, SLOT(MoveDaBall(VectorX,VectorY)));}
@Thanks
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Hi,
You don't call start nor end on your QPainter. These are need to tell Qt that you are painting something and when you did end the painting
Hope it helps
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Ehm... I didn't get it... I'm a newbie and I still need to learn a lot.
When I say:
@
mambo=new Objects;
QGridLayout *Layout = new QGridLayout;
Layout->addWidget(mambo);
setLayout(Layout);
@It doesn't mean that I the program draw everything in the layout? If not how do I solve the problem?
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It will show the widget, but you must ensure that the painting is done correctly first.
I've re-read QPainter's documentation, begin/end are not mandatory the way you use QPainter. However, I have not seen implementation using two QPainter on the same device, so it might be a source of problem.
Since you are completely new, you should go step by step. As silly as it may sound, start by painting a rect, once you have it on screen properly. Add the different pieces gradually.
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Few things here.
First - you should paint in
@void Objects::paintEvent(QPaintEvent *) override@
Qt doesn't know anything about
@void Objects::PaintObjects(QPaintEvent *)@
so unless you're not giving us the whole code this will never be called.Second, as SGaist said, you should use only one painter on a paint device (in your case "this" widget). There's just no point in having two there.
