如何在 QGraphicsScene 上绘制一个点(鼠标单击)? [英] How to draw a point (on mouseclick) on a QGraphicsScene?

问题描述

我有以下代码来设置 QGraphicsScene.我希望单击场景并在我单击的位置绘制一个点.我怎么能这样做?这是我当前的代码:

I have the following code to set up a QGraphicsScene. I wish to click on the scene and draw a point at the location I've clicked. How could I do this? This is my current code:

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    QGraphicsScene *scene;
    QGraphicsView *view = new QGraphicsView(this);

    view->setGeometry(QRect(20, 50, 400, 400));
    scene = new QGraphicsScene(50, 50, 350, 350);
    view->setScene(scene);
}

推荐答案

UPDATE:有一个名为 QGraphicsSceneMouseEvent 的新类，它使这更容易一些.我刚刚在这里完成了一个使用它的例子:

UPDATE: There is a new class called QGraphicsSceneMouseEvent that makes this a little easier. I just finished an example using it here:

https://stackoverflow.com/a/26903599/999943

它与下面的答案的不同之处在于它子类化 QGraphicsScene，而不是 QGraphicsView，并且它使用 mouseEvent->scenePos() 所以无需手动映射坐标.

It differs with the answer below in that it subclasses QGraphicsScene, not QGraphicsView, and it uses mouseEvent->scenePos() so there isn't a need to manually map coordinates.

您走在正确的轨道上，但您还有一些路要走.

You are on the right track, but you still have a little more to go.

您需要子类化 QGraphicsView 才能使用 QMouseEvent 通过鼠标按下或释放鼠标来执行某些操作.

You need to subclass QGraphicsView to be able to do something with mouse presses or with mouse releases using QMouseEvent.

    #include <QGraphicsView>
    #include <QGraphicsScene>
    #include <QGraphicsEllipseItem>
    #include <QMouseEvent>

    class MyQGraphicsView : public QGraphicsView
    {
        Q_OBJECT
    public:
        explicit MyQGraphicsView(QWidget *parent = 0);

    signals:

    public slots:
        void mousePressEvent(QMouseEvent * e);
        // void mouseReleaseEvent(QMouseEvent * e);
        // void mouseDoubleClickEvent(QMouseEvent * e);
        // void mouseMoveEvent(QMouseEvent * e);
    private:
        QGraphicsScene * scene;
    };

QGraphicsView 本身没有无量纲点.您可能希望使用 QGraphicsEllipse 项目或简单地使用半径非常小的 scene->addEllipseItem().

QGraphicsView doesn't natively have dimension-less points. You will probably want to use QGraphicsEllipse item or simply, scene->addEllipseItem() with a very small radius.

    #include "myqgraphicsview.h"
    #include <QPointF>

    MyQGraphicsView::MyQGraphicsView(QWidget *parent) :
        QGraphicsView(parent)
    {
        scene = new QGraphicsScene();
        this->setSceneRect(50, 50, 350, 350);
        this->setScene(scene);
    }

    void MyQGraphicsView::mousePressEvent(QMouseEvent * e)
    {
        double rad = 1;
        QPointF pt = mapToScene(e->pos());
        scene->addEllipse(pt.x()-rad, pt.y()-rad, rad*2.0, rad*2.0, 
            QPen(), QBrush(Qt::SolidPattern));
    }

注意 mapToScene() 的用法，使事件的 pos() 正确映射到鼠标在场景上点击的位置.

Note the usage of mapToScene() to make the pos() of the event map correctly to where the mouse is clicked on the scene.

如果要使用表单，则需要将子类 QGraphicsView 的实例添加到 ui 的 centralWidget 布局中.

You need to add an instance of your subclassed QGraphicsView to the centralWidget's layout of your ui if you are going to use a form.

    QGridLayout * gridLayout = new QGridLayout(ui->centralWidget);
    gridLayout->addWidget( new MyQGraphicsView() );

或者如果您的 ui 已经有布局，它将如下所示:

or if your ui has a layout already it will look like this:

    ui->centralWidget->layout()->addWidget( new MyGraphicsView() );

如果你不使用 QMainWindow 和一个表单，你可以将它添加到一个 QWidget 如果你为它设置一个布局然后添加你的 QGraphicsView 以类似的方式到该布局.如果您不想在 QGraphicsView 周围留出边距，只需调用 show 即可，不要将其放在不同的布局中.

If you don't use a QMainWindow and a form, you can add it to a QWidget if you set a layout for it and then add your QGraphicsView to that layout in a similar manner. If you don't want a margin around your QGraphicsView, just call show on it and don't put it inside a different layout.

    #include <QtGui/QApplication>
    #include "myqgraphicsview.h"

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

        MyQGraphicsView view;
        view.show();

        return a.exec();
    }

就是这样.现在您对 QGraphicsView 及其与鼠标的交互很危险.

And that's it. Now you are dangerous with QGraphicsView's and their interaction with the mouse.

请务必阅读和研究 Qt 的图形视图框架和相关examples在使用QGraphicsView 和 QGraphicsScene.它们是非常强大的 2D 图形工具，可能需要一些学习曲线，但它们值得.

Be sure to read and study about Qt's Graphics View Framework and the related examples to be effective when using QGraphicsView and QGraphicsScene. They are very powerful tools for 2D graphics and can have a bit of a learning curve but they are worth it.

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