Applying Blur Effects in Qt Widgets: QGraphicsBlurEffect::blurRadius and Beyond

Purpose

• A lower radius produces a subtler blur, preserving more detail.
• A higher radius results in a stronger blur, making underlying content less distinct.
• Controls the intensity of the blur effect applied by a QGraphicsBlurEffect object.

Context

• It's a subclass of QGraphicsEffect, allowing you to add visual effects to Qt graphics items.
• QGraphicsBlurEffect is part of the Qt Widgets library, which provides building blocks for creating graphical user interfaces (GUIs) in Qt applications.

Member Function

• Setter
  Updates the blur radius to the specified value and emits the blurRadiusChanged signal.
• Getter
  Returns the current blur radius value (in device-independent pixels).
• blurRadius() is a getter and setter function for the blur radius property.

Usage

1. QGraphicsBlurEffect* blurEffect = new QGraphicsBlurEffect;
   

2. Set the blur radius
   

   blurEffect->setBlurRadius(10.0); // Sets a 10-pixel blur
   

   • You can dynamically adjust the blur radius later on.

3. Apply the effect to a graphics item
   

   // Assuming you have a graphics item named 'myItem'
   myItem->setGraphicsEffect(blurEffect);
   

Additional Notes

• Consider using QGraphicsBlurEffect::setBlurHints to optimize rendering performance or quality based on your use case.
• The blur radius is device-independent, meaning it's not affected by scaling.
• The default blur radius is 5 pixels.

Example

#include <QApplication>
#include <QWidget>
#include <QVBoxLayout>
#include <QLabel>
#include <QGraphicsBlurEffect>

int main(int argc, char *argv[]) {
    QApplication app(argc, argv);

    QWidget window;
    QVBoxLayout layout;

    QLabel* label = new QLabel("This text has a blur effect");
    layout.addWidget(label);

    QGraphicsBlurEffect* blurEffect = new QGraphicsBlurEffect;
    label->setGraphicsEffect(blurEffect);
    blurEffect->setBlurRadius(15.0); // Adjust blur intensity

    window.setLayout(&layout);
    window.show();

    return app.exec();
}

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Dynamically Changing Blur Radius

This code shows how to adjust the blur radius based on user interaction (e.g., slider movement):

#include <QApplication>
#include <QWidget>
#include <QVBoxLayout>
#include <QLabel>
#include <QGraphicsBlurEffect>
#include <QSlider>

int main(int argc, char *argv[]) {
    QApplication app(argc, argv);

    QWidget window;
    QVBoxLayout layout;

    QLabel* label = new QLabel("Blur this text!");
    layout.addWidget(label);

    QGraphicsBlurEffect* blurEffect = new QGraphicsBlurEffect;
    label->setGraphicsEffect(blurEffect);

    // Slider to control blur radius
    QSlider* blurSlider = new QSlider(Qt::Horizontal);
    blurSlider->setRange(0, 20); // Adjust range as needed
    blurSlider->setValue(10); // Initial blur radius
    layout.addWidget(blurSlider);

    // Connect slider value change to update blur radius
    QObject::connect(blurSlider, &QSlider::valueChanged, blurEffect, &QGraphicsBlurEffect::setBlurRadius);

    window.setLayout(&layout);
    window.show();

    return app.exec();
}

Blurring a Specific Area

This example demonstrates applying a blur effect to a widget within a layout:

#include <QApplication>
#include <QWidget>
#include <QVBoxLayout>
#include <QLabel>
#include <QGraphicsBlurEffect>

int main(int argc, char *argv[]) {
    QApplication app(argc, argv);

    QWidget window;
    QVBoxLayout layout;

    QWidget* blurredWidget = new QWidget; // Widget to be blurred
    blurredWidget->setStyleSheet("background-color: lightblue;"); // Set a background color
    layout.addWidget(blurredWidget);

    QGraphicsBlurEffect* blurEffect = new QGraphicsBlurEffect;
    blurredWidget->setGraphicsEffect(blurEffect);
    blurEffect->setBlurRadius(8.0);

    window.setLayout(&layout);
    window.show();

    return app.exec();
}

Different Blur Hints

This code showcases using QGraphicsBlurEffect::setBlurHints with different blur hints:

#include <QApplication>
#include <QWidget>
#include <QVBoxLayout>
#include <QLabel>
#include <QGraphicsBlurEffect>

int main(int argc, char *argv[]) {
    QApplication app(argc, argv);

    QWidget window;
    QVBoxLayout layout;

    QLabel* label1 = new QLabel("Blur 1 (IgnoringAlpha)");
    layout.addWidget(label1);

    QGraphicsBlurEffect* blurEffect1 = new QGraphicsBlurEffect;
    label1->setGraphicsEffect(blurEffect1);
    blurEffect1->setBlurRadius(10.0);
    blurEffect1->setBlurHints(QGraphicsBlurEffect::IgnoringAlphaChannel);

    QLabel* label2 = new QLabel("Blur 2 (QualityPerformance)");
    layout.addWidget(label2);

    QGraphicsBlurEffect* blurEffect2 = new QGraphicsBlurEffect;
    label2->setGraphicsEffect(blurEffect2);
    blurEffect2->setBlurRadius(10.0);
    blurEffect2->setBlurHints(QGraphicsBlurEffect::QualityPerformance);

    window.setLayout(&layout);
    window.show();

    return app.exec();
}

---

CSS filter: blur()

• Syntax: widget { filter: blur(radius); } (replace radius with the desired blur amount in pixels).
• It provides similar functionality to QGraphicsBlurEffect::blurRadius but might offer better performance depending on your use case.
• If you're working with Qt Quick (QML) or using stylesheets within Qt Widgets, consider using the CSS filter: blur() property.

Custom Shaders (Advanced)

• However, this approach requires a deeper understanding of OpenGL and shader programming.
• This allows for fine-tuning the blur algorithm and potentially achieving specific visual effects that QGraphicsBlurEffect might not offer directly.
• For more granular control over the blur effect, you can explore creating custom shaders using OpenGL.

Third-Party Libraries

• Thoroughly research and evaluate such libraries before integrating them into your project.
• While less common, some third-party libraries might offer alternative blur implementations with features that might suit your needs.

• Fine-Grained Control
  If you need precise control over the blur algorithm or require specific visual effects, custom shaders are an option, but be aware of the increased complexity.
• Performance
  For performance-critical scenarios, consider using CSS filter: blur() as it might be more lightweight.
• Simplicity
  If you need a straightforward blur effect and don't require advanced customization, QGraphicsBlurEffect::blurRadius is a good choice.