QT Scene Graph使用QSGTransformNode做出鼠标点击拖动效果

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已于 2023-05-20 21:44:53 修改

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文章标签： qt

于 2023-05-20 21:32:29 首次发布

本文链接：https://blog.youkuaiyun.com/weixin_42100490/article/details/130785895

文章介绍了如何在Qt中利用QSGTransformNode处理图形变换，特别是通过鼠标事件实现矩阵平移和旋转，以及更新图形节点的方法。示例代码展示了如何在QQuickItem基础上添加鼠标监听，改变QMatrix4x4矩阵来更新整个图形的视觉效果。

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在寻找如何使用QSGTransformNode的过程中发现如下图片，于是尝试一下
在这里插入图片描述

效果

关键部分

基本图像都是由这些QSGNode构成的，Node之间存在父与子的关系，改变了父就会改变所有子节点。例如我增加了Transform效果，做一个平移或者旋转，需要跟着运动的就是它的子节点。

下面是部分代码，在官方例子基础上增加的。这里关键是使用了quick item类的鼠标点击事件。

Graph::Graph()
    : m_samplesChanged(false)
    , m_geometryChanged(false)
    ,m_matrixChanged(false)
{
    setAcceptedMouseButtons(Qt::LeftButton
        | Qt::RightButton
        | Qt::MiddleButton);
    setFlag(ItemHasContents, true);
}
void  Graph::mousePressEvent(QMouseEvent* event)
{
    event->accept();
    mouse_press = event->localPos();
}

void  Graph::mouseMoveEvent(QMouseEvent* event)
{

    event->accept();
    QPointF pos = event->localPos();
    //QMatrix4x4的平移方法
    matrix.translate(pos.x() - mouse_press.x(), pos.y() - mouse_press.y());
    //也可以使用他的别的方法，比如旋转 matrix.rotate(30,0,1,0)                        // 绕着y轴旋转30度
    m_matrixChanged=true;
    mouse_press = event->localPos();
    update();
}

void  Graph::mouseReleaseEvent(QMouseEvent* event)
{
    event->accept();
    update();
}

这里是把原本继承的GsgNode改为QSGTransformNode，这样我使用GraphNode的QSGTransformNode::setMatrix方法就能进行整个图形的变换。


class GraphNode : public QSGTransformNode
{
public:
    NoisyNode *background;
    GridNode *grid;
    LineNode *line;
    LineNode *shadow;
};

全部代码


#ifndef GRAPH_H
#define GRAPH_H

#include <QMatrix4x4>
#include <QQuickItem>

class Graph : public QQuickItem
{
    Q_OBJECT
    QML_ELEMENT
public:
    Graph();

    void mousePressEvent(QMouseEvent *event);
    void mouseMoveEvent(QMouseEvent *event);
    void mouseReleaseEvent(QMouseEvent *event);
protected:
    QSGNode *updatePaintNode(QSGNode *, UpdatePaintNodeData *);
    void geometryChange(const QRectF &newGeometry, const QRectF &oldGeometry);

public slots:
    void appendSample(qreal value);
    void removeFirstSample();

private:
    QList<qreal> m_samples;
    QMatrix4x4 matrix;
 QPointF mouse_press;
    bool m_samplesChanged;
    bool m_geometryChanged;
    bool m_matrixChanged;
};

#endif // GRAPH_H



#include "graph.h"

#include "noisynode.h"
#include "gridnode.h"
#include "linenode.h"

Graph::Graph()
    : m_samplesChanged(false)
    , m_geometryChanged(false)
    ,m_matrixChanged(false)
{
    setAcceptedMouseButtons(Qt::LeftButton
        | Qt::RightButton
        | Qt::MiddleButton);
    setFlag(ItemHasContents, true);
}


void Graph::appendSample(qreal value)
{
    m_samples << value;
    m_samplesChanged = true;
    update();
}


void Graph::removeFirstSample()
{
    m_samples.removeFirst();
    m_samplesChanged = true;
    update();
}

void  Graph::mousePressEvent(QMouseEvent* event)
{
    event->accept();
    mouse_press = event->localPos();
}

void  Graph::mouseMoveEvent(QMouseEvent* event)
{

    event->accept();
    QPointF pos = event->localPos();
    matrix.translate(pos.x() - mouse_press.x(), pos.y() - mouse_press.y());
    m_matrixChanged=true;
    mouse_press = event->localPos();
    update();
}

void  Graph::mouseReleaseEvent(QMouseEvent* event)
{
    event->accept();
    update();
}



void Graph::geometryChange(const QRectF &newGeometry, const QRectF &oldGeometry)
{
    m_geometryChanged = true;
    update();
    QQuickItem::geometryChange(newGeometry, oldGeometry);
}


class GraphNode : public QSGTransformNode
{
public:
    NoisyNode *background;
    GridNode *grid;
    LineNode *line;
    LineNode *shadow;
};


QSGNode *Graph::updatePaintNode(QSGNode *oldNode, UpdatePaintNodeData *)
{
    GraphNode *n= static_cast<GraphNode *>(oldNode);

    QRectF rect = boundingRect();

    if (rect.isEmpty()) {
        delete n;
        return nullptr;
    }

    if (!n) {

        n = new GraphNode();

        n->background = new NoisyNode(window());
        n->grid = new GridNode();
        n->line = new LineNode(10, 0.5, QColor("steelblue"));
        n->shadow = new LineNode(20, 0.2f, QColor::fromRgbF(0.2, 0.2, 0.2, 0.4));

        matrix=n->matrix();

        n->appendChildNode(n->background);
        n->appendChildNode(n->grid);
        n->appendChildNode(n->shadow);
        n->appendChildNode(n->line);

    }

    if(m_matrixChanged )
    {
        n->setMatrix(matrix);
    }

    if (m_geometryChanged) {
        n->background->setRect(rect);
        n->grid->setRect(rect);
    }

    if (m_geometryChanged || m_samplesChanged) {
        n->line->updateGeometry(rect, m_samples);
        // We don't need to calculate the geometry twice, so just steal it from the other one...
        n->shadow->setGeometry(n->line->geometry());
    }


    m_geometryChanged = false;
    m_samplesChanged = false;
    m_matrixChanged = false;

    return n;
}