QML使用QQuickPaintedItem，QQuickItem来加载QImage图片

继承QQuickPaintedItem

头文件：PaintItem.h

#include <QQuickPaintedItem>
#include <QImage>
#include <QPainter>
 
class PaintItem : public QQuickPaintedItem
{
    Q_OBJECT
public:
    explicit PaintItem(QQuickItem *parent = nullptr);
 
public slots:
    void updateImage(const QImage &);
 
protected:
    void paint(QPainter *painter);
 
private:
    QImage m_imageThumb;
};

实现：PaintItem.cpp

#include "paintitem.h"
 
PaintItem::PaintItem(QQuickItem *parent) : QQuickItem(parent)
{
    //默认图片
    m_imageThumb = QImage(":/Image/background.png");
}
 
void PaintItem::updateImage(const QImage &image)
{
    m_imageThumb = image;
    update();
}
 
void PaintItem::paint(QPainter *painter)
{
    painter->drawImage(this->boundingRect(), m_imageThumb);
}

main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include "paintitem.h"
 
int main(int argc, char *argv[])
{
#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
#endif
 
    QGuiApplication app(argc, argv);
 
    //注册类
    qmlRegisterType<PaintItem>("PaintItemModule",1,0,"PaintItem");
 
    QQmlApplicationEngine engine;
 
    const QUrl url(QStringLiteral("qrc:/main.qml"));
    QObject::connect(&engine, &QQmlApplicationEngine::objectCreated,
                     &app, [url](QObject *obj, const QUrl &objUrl) {
        if (!obj && url == objUrl)
            QCoreApplication::exit(-1);
    }, Qt::QueuedConnection);
    engine.load(url);
 
    return app.exec();
}

Qml文件text.qml

import QtQuick 2.12
import QtQuick.Controls 2.5
import PaintItemModule 1.0
 
Rectangle {
    id: rectangle
    anchors.fill: parent
 
    PaintItem {
        id: paintItem
        transformOrigin: Item.Center
        anchors.horizontalCenter: parent.horizontalCenter
        anchors.verticalCenter: parent.verticalCenter
    }
}

继承QQuickItem重写updatePaintNode

头文件：PaintItem.h

#include <QQuickItem>
#include <QSGNode>
#include <QSGSimpleRectNode>
#include <QSGSimpleTextureNode>
#include <QQuickWindow>
#include <QImage>
 
class PaintItem : public QQuickItem
{
    Q_OBJECT
public:
    explicit PaintItem(QQuickItem *parent = nullptr);
 
public slots:
    void updateImage(const QImage &);
 
protected:
    QSGNode * updatePaintNode(QSGNode *oldNode, UpdatePaintNodeData *) override;
 
private:
    QImage m_imageThumb;
};

实现PaintItem.cpp

#include "paintitem.h"
 
PaintItem::PaintItem(QQuickItem *parent) : QQuickItem(parent)
{
    //这句不加会报错
    setFlag(ItemHasContents, true);
    //默认图片
    m_imageThumb = QImage(":/Image/background.png");
}
 
void PaintItem::updateImage(const QImage &image)
{
    m_imageThumb = image;
    update();
}
 
QSGNode * PaintItem::updatePaintNode(QSGNode *oldNode, QQuickItem::UpdatePaintNodeData *)
{
    auto node = dynamic_cast<QSGSimpleTextureNode *>(oldNode);
 
    if(!node){
        node = new QSGSimpleTextureNode();
    }
 
    QSGTexture *m_texture = window()->createTextureFromImage(m_imageThumb, QQuickWindow::TextureIsOpaque);
    node->setOwnsTexture(true);
    node->setRect(boundingRect());
    node->markDirty(QSGNode::DirtyForceUpdate);
    node->setTexture(m_texture);
 
    return node;
}