Fading the picture in

When the user opens a picture, we want to fade in the image by playing with its opacity. The classes QLabel or QWidget do not provide an opacity property. However, we can add a visual effect to any QWidget using a QGraphicsEffect. For this animation, we will use QGraphicsOpacityEffect to provide an opacity property.

Here is a schema to describe the role of each one:

In our case, the QWidget class is our QLabel and the QGraphicsEffect class is QGraphicsOpacityEffect. Qt provides the Graphics Effect system to alter the rendering of a QWidget class. The abstract class QGraphicsEffect has a pure virtual method draw() that is implemented by each graphics effect.

We can now update the MainWindow.h according to the next snippet:

#include <QPropertyAnimation> 
#include <QGraphicsOpacityEffect> 
 
class MainWindow : public QMainWindow 
{ 
    ... 
private: 
    ... 
    void initAnimations(); 
private: 
    ... 
    QPropertyAnimation mLoadPictureAnimation; 
    QGraphicsOpacityEffect...