QT 跟踪鼠标轨迹

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QT 跟踪鼠标轨迹

一.普通窗口的鼠标轨迹

1.获取鼠标的位置，可以通过调用窗口的鼠标移动事件函数 mouseMoveEvent(QMouseEvent *);

再通过鼠标事件的 pos()函数获取鼠标位置。

但是,仅指定mouseMoveEvent(QMouseEvent *)函数，还不够，此时，需要在窗口内按下鼠标左键或者右键，然后才能出发 mouseMoveEvent(QMouseEvent *) 函数。

2.而很多情况下，我们希望的是，不按下鼠标，仅仅移动鼠标就可以获取鼠标的轨迹。该怎么做？
查询，Qt 助手资料：
[virtual protected] void QWidget::mouseMoveEvent(QMouseEvent *event)
This event handler, for event event, can be reimplemented in a subclass to receive mouse move events for the widget.
If mouse tracking is switched off, mouse move events only occur if a mouse button is pressed while the mouse is being moved. If mouse tracking is switched on, mouse move events occur even if no mouse button is pressed.
QMouseEvent::pos() reports the position of the mouse cursor, relative to this widget. For press and release events, the position is usually the same as the position of the last mouse move event, but it might be different if the user’s hand shakes. This is a feature of the underlying window system, not Qt.
If you want to show a tooltip immediately, while the mouse is moving (e.g., to get the mouse coordinates with QMouseEvent::pos() and show them as a tooltip), you must first enable mouse tracking as described above. Then, to ensure that the tooltip is updated immediately, you must call QToolTip::showText() instead of setToolTip() in your implementation of mouseMoveEvent().
See also setMouseTracking(), mousePressEvent(), mouseReleaseEvent(), mouseDoubleClickEvent(), event(), QMouseEvent, and Scribble Example.

意思是说，还需要对对应的窗口调用 setMouseTracking(true) 函数。
ps：对于QWidget的嵌套，子窗口要不按下鼠标就能捕获鼠标轨迹，只设置子窗口的 setMouseTracking(true) 是不够的！还需要对每一层父窗口设置 setMouseTracking(true)。

3.举个栗子说明吧，新建一个普通mainwindow 工程，然后在 centralWidget 中拖入一个widget。在mouseMoveEvent()中获取鼠标的坐标位置，并通过label显示出来。代码如下：
mianwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QLabel>
#include <QMouseEvent>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = nullptr);
    ~MainWindow();

private:
    Ui::MainWindow *ui;

    QLabel *label;

protected:
    void mouseMoveEvent(QMouseEvent *p);
};

#endif // MAINWINDOW_H

mianwindow.h.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QDebug>

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

    label = new QLabel(this);

    this->setMouseTracking(true);
    ui->centralWidget->setMouseTracking(true);
    ui->widget->setMouseTracking(true);
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::mouseMoveEvent(QMouseEvent *p)
{
    qDebug()<<p<<p->pos();
    QString text;
    text.sprintf( "(%d,%d)", p->x(), p->y() );
    label->setText(text);
    label->move(p->pos());
}

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