src_gui_effects_qgraphicseffect.cpp

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// Copyright (C) 2016 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
 
#include <QGraphicsEffect>
#include <QPainter>
#include <QLinearGradient>
#include <QGraphicsOpacityEffect>
#include <QRect>
 
class MyGraphicsEffect : public QGraphicsEffect
{
    Q_OBJECT
public:
    void draw(QPainter *painter) override;
};
 
class MyGraphicsOpacityEffect : public QGraphicsOpacityEffect
{
    Q_OBJECT
public:
    void draw(QPainter *painter) override;
private:
    qreal m_opacity = 1.0;
};
 
//! [0]
void MyGraphicsOpacityEffect::draw(QPainter *painter)
{
    // Fully opaque; draw directly without going through a pixmap.
    if (qFuzzyCompare(m_opacity, 1)) {
        drawSource(painter);
        return;
    }
    //...
}
//! [0]
 
//! [1]
void MyGraphicsEffect::draw(QPainter *painter)
{
    //...
    QPoint offset;
    if (sourceIsPixmap()) {
        // No point in drawing in device coordinates (pixmap will be scaled anyways).
        const QPixmap pixmap = sourcePixmap(Qt::LogicalCoordinates, &offset);
        //...
        painter->drawPixmap(offset, pixmap);
    } else {
        // Draw pixmap in device coordinates to avoid pixmap scaling;
        const QPixmap pixmap = sourcePixmap(Qt::DeviceCoordinates, &offset);
        painter->setWorldTransform(QTransform());
        //...
        painter->drawPixmap(offset, pixmap);
    }
    //...
}
//! [1]
 
void example()
{
    QRect rect;
 
    //! [2]
    //...
    QLinearGradient alphaGradient(rect.topLeft(), rect.bottomLeft());
    alphaGradient.setColorAt(0.0, Qt::transparent);
    alphaGradient.setColorAt(0.5, Qt::black);
    alphaGradient.setColorAt(1.0, Qt::transparent);
    QGraphicsOpacityEffect *effect = new QGraphicsOpacityEffect;
    effect->setOpacityMask(alphaGradient);
    //...
    //! [2]
}