Implementing paint()

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

Code:

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#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

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 :

Code:

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bColor = Qt::red;
update();

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2) In your paint method

Code:

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painter->setBrush(bColor);

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I think that should work.

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 :confused: It's al quit obvious in the screens I added.

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

Code:

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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);		
}

---

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):

Code:

---

#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

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) :

Code:

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update( boundingRect() );

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