QGraphicsItem how to change the boundary colors of the rectangale

Qt Enthusiast

I have following class

class myItem::public QGraphicsItem
{

private:
QRectF rect;
QBrush brush;
}

Can you write the sample code , for the same

How can I use brush to just color the boundary color and keep the fill color as same

mrjj

Hi
Where you draw it. just change the pen.
http://doc.qt.io/qt-5/qpainter.html#pen
QPen mypen(White)
painter.setPen(mypen)

please see the docs
http://doc.qt.io/qt-5/qpen.html

Qt Enthusiast

Once it is drawn , I want to change the boundary on already drawn rectangle on a button click

For example I want to change the boundary when on a button click and I have object of QGraphicitem , if you could guide me

Currently I have slot was following but clears the fill color of the QGraphictsitem

class myItem :: QGraphictsitem {

private
}

void GQPhyItem::updateConfig()
{
QColor color = QColor(Qt::red);
brush.setColor(color);
brush.setStyle(color);
}

mrjj

@Qt-Enthusiast

Well first u need to be able to change it. and get the effect you want.

When that works, you need to make a slot in the item so you can
ask it to change.

Then you need to hook up the button so it triggers this slots to change the pen.

Qt Enthusiast

if you could point me to sample code that will be helpful

mrjj

@Qt-Enthusiast
sorry didnt see any sample code.
Its covered by QPainter and QPens docs.

Qt Enthusiast

how to get pointer of Qpainter and QPen
objects in QGraphicsitem

mrjj

@Qt-Enthusiast
In paintevent you have painter.
it has both.

Qt Enthusiast

so you mean after the slot
can I need to call i assume you have myItem::paintEvent ? is called automatcially after the slot

mrjj

@Qt-Enthusiast

can I need to call i assume you have myItem::paintEvent ? is called automatcially after the slot

Not sure what u say here :)

? Offline

Hi! Here is a minimal example. Note that we need to derive our custom item not from QGraphicsItem but from QGraphicsObject so that we can use signals and slots with it.

mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"

#include <QGraphicsScene>
#include "myitem.h"

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    QGraphicsScene *scene = new QGraphicsScene;
    MyItem *myItem = new MyItem();
    scene->addItem( myItem );
    ui->graphicsView->setScene(scene);
    // ui->pushButton_2 is the button to toggle the color of your rectangle
    connect(ui->pushButton_2, &QPushButton::clicked, myItem, &MyItem::toggleColor);
}

myitem.h

#ifndef MYITEM_H
#define MYITEM_H

#include <QGraphicsObject> 

// it uses signals & slots, so inheriting from QGraphicsItem wouldn't be enough
class MyItem : public QGraphicsObject
{
    Q_OBJECT
public:
    MyItem(QGraphicsItem *parent = Q_NULLPTR);
    QRectF boundingRect() const override;
    void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget) override;

public slots:
    void toggleColor();

private:
    const qreal m_penWidth = 10;
    bool m_color = false; // color of the rectangle; true = lime, false = purple
};

#endif // MYITEM_H

myitem.cpp

#include "myitem.h"

#include <QPen>
#include <QPainter>


MyItem::MyItem(QGraphicsItem *parent)
    : QGraphicsObject(parent)
{
}

QRectF MyItem::boundingRect() const
{
    return QRectF(-20 - m_penWidth / 2, -20 - m_penWidth / 2, 40 + m_penWidth, 40 + m_penWidth);
}

void MyItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
    Q_UNUSED(option)
    Q_UNUSED(widget)
    QPen pen( m_color ? QColor("lime") : QColor("purple") );
    pen.setWidth(m_penWidth);
    painter->setPen(pen);
    painter->drawRect(-20, -20, 40, 40);
}

void MyItem::toggleColor()
{
    m_color = !m_color;
    update();
}

Hope it helps!

Qt Enthusiast

One more question , how to get filled color of colored QGraphicsitem filled rectangle

CorD SaC

@Wieland said in QGraphicsItem how to change the boundary colors of the rectangale:

ere is a minimal example. Note that we need to derive our custom item not from QGraphicsItem but from QGraphicsObject so that we can use signals and slots with it.
mainwindow.cpp
#include "mainwindow.h"
#include "ui_mainwindow.h"

#include <QGraphicsScene>
#include "myitem.h"

MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),

Could you please explain why this error occur. ```
error: 'myitem' does not name a type
myitem *myitem = new myitem;

mrjj

@CorD-SaC

The myitem.h is a custom file

if you do not have it, it means that
it dont know what myitem is for a class.

'myitem' does not name a type
=
What the heck is "myitem" , compiler says

CorD SaC

@mrjj

problem is solved,I change the code, myitem *mi = new myitem(); instead of
//myitem *myitem = new myitem(); I don't know what was the reason,however after change the code like this,problem solved.

mrjj

Oh the type (of the class) was used as variable also

like
int *int = new int()

that is not allowed :)

CorD SaC

@mrjj

Ooops,thanks :)