Implementing paint()

[Wirloff]

Hi, I have a class named "Graphics" which is derived from "QGraphicsItem" and represents a small green rectangle:

#include <QtGui>
#include <QPainter>
#include <iostream>
#include <QColor>
 
#include "Graphics.hpp"
 
Graphics::Graphics(): color(qrand() % 256, qrand() % 256, qrand() % 256)
 {
     setCursor(Qt::OpenHandCursor);
  }
 
 QRectF Graphics::boundingRect() const
 {
     return QRectF(0, 0, 25, 25);
 }
 
 void Graphics::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
 {
     Q_UNUSED(option);
     Q_UNUSED(widget);
     painter->setPen(Qt::NoPen);
     painter->setBrush(Qt::green);
     painter->drawRect(0, 0, 10, 20);
 
 }
 
 void Graphics::mousePressEvent(QGraphicsSceneMouseEvent *event)
 {
 
 }

#include <QtGui>
#include <QPainter>
#include <iostream>
#include <QColor>

#include "Graphics.hpp"

Graphics::Graphics(): color(qrand() % 256, qrand() % 256, qrand() % 256)
 {
     setCursor(Qt::OpenHandCursor);
  }

 QRectF Graphics::boundingRect() const
 {
     return QRectF(0, 0, 25, 25);
 }

 void Graphics::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
 {
     Q_UNUSED(option);
     Q_UNUSED(widget);
     painter->setPen(Qt::NoPen);
     painter->setBrush(Qt::green);
     painter->drawRect(0, 0, 10, 20);
    
 }

 void Graphics::mousePressEvent(QGraphicsSceneMouseEvent *event)
 {
    
 }

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But now, when clicked on a rectangle, I want it's color to change to red. But I have read that there is no such thing as a "repaint" methode. Anoyne who can help me, and tell me how to get the clicked rectangle red? I have no idea what to do within the mouseEvent

[guilugi]

Well, the method is quite simple

You just have to use a variable to store your color, let's say bColor,
set by default with Qt::green.

1) In your mousePressEvent, you change this variable :

bColor = Qt::red;
update();

bColor = Qt::red;
update();

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2) In your paint method

painter->setBrush(bColor);

painter->setBrush(bColor);

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I think that should work.

[Wirloff]

Thanx, update() was the methode that I was searching for. But now I have an other (weird) problem. I have added a 3 little zipfiles with 3 screenshots, which can show you the problem:

- When I click on a rectangle (I have 256 rectangels drawn next to each other on a GraphicsScene), not only thát rectangle is redrawn in red, but 2,5(!) rectangles are redrawn in red.

-After coloring some rectangles red, if I then scroll to the right, all the rectangles that weren't visible yet outside the screen, also have changed color It's al quit obvious in the screens I added.

The method setupGraphics() from class MainWindow looks like this:

void MainWindow::setupGraphics()
{
    QGraphicsScene *scene = new QGraphicsScene();;
	 for (int i = 0; i < 256; ++i)
     {
        Graphics* item = new Graphics;
         item->setPos(i*12,12);
         scene->addItem(item);
     }
    	m_ui.graphicsView->setScene(scene);		
}

void MainWindow::setupGraphics()
{
    QGraphicsScene *scene = new QGraphicsScene();;
	 for (int i = 0; i < 256; ++i)
     {
        Graphics* item = new Graphics;
         item->setPos(i*12,12);
         scene->addItem(item);
     }
    	m_ui.graphicsView->setScene(scene);		
}

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This draws the 256 rectangles for the first time....

Anyone who knows what I have to do so that only the rectangle which I have clicked on changes from color? Or what I'm doing wrong?? This is my code of the GraphicsItem again I have added a bool to control if an item has been clicked or not):

#include <QtGui>
#include <QPainter>
#include <iostream>
#include <QColor>
 
#include "Graphics.hpp"
 
 
bool used;
 
Graphics::Graphics(): color(qrand() % 256, qrand() % 256, qrand() % 256)
 {
     used=false;
  }
 
 QRectF Graphics::boundingRect() const
 {
     return QRectF(0, 0, 25, 25);
 }
 
 void Graphics::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
 {
     Q_UNUSED(option);
     Q_UNUSED(widget);
     painter->setPen(Qt::NoPen);
     if (used)
     {
     painter->setBrush(Qt::red);
     }
     else
     {
     painter->setBrush(Qt::green);
     }
     painter->drawRect(0, 0, 10, 20);
 
 }
 
 void Graphics::mousePressEvent(QGraphicsSceneMouseEvent *event)
 {
    if (!used)
    {
        used=true;
    }
    else
    {
        used=false;
    }
 
    update();
 
 }

#include <QtGui>
#include <QPainter>
#include <iostream>
#include <QColor>

#include "Graphics.hpp"


bool used;

Graphics::Graphics(): color(qrand() % 256, qrand() % 256, qrand() % 256)
 {
     used=false;
  }

 QRectF Graphics::boundingRect() const
 {
     return QRectF(0, 0, 25, 25);
 }

 void Graphics::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
 {
     Q_UNUSED(option);
     Q_UNUSED(widget);
     painter->setPen(Qt::NoPen);
     if (used)
     {
     painter->setBrush(Qt::red);
     }
     else
     {
     painter->setBrush(Qt::green);
     }
     painter->drawRect(0, 0, 10, 20);
    
 }

 void Graphics::mousePressEvent(QGraphicsSceneMouseEvent *event)
 {
    if (!used)
    {
        used=true;
    }
    else
    {
        used=false;
    }
        
    update();
        
 }

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Thanx in advance

[guilugi]

Okay, I got it.

When you call update() without specifying a clip rect, it may cause adjacent items to be repainted as well...and that would explain your issues.
Read closely the docs about this method, it's well said

To avoid this, call update() with a specified rect (the current item rect) :

update( boundingRect() );

update( boundingRect() );

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