根据滑条值改变指针角度

#ifndef MAINWINDOW_H

#define MAINWINDOW_H

#include <QMainWindow>

#include <QGraphicsScene>

#include <QGraphicsPixmapItem>

namespace Ui {

class MainWindow;

}

class MainWindow : public QMainWindow

{

    Q_OBJECT

public:

    explicit MainWindow(QWidget *parent = nullptr);

    ~MainWindow();

    QGraphicsScene *scene;

    QGraphicsPixmapItem *pointer;

    QPixmap pix1;

    QPixmap pix2;

    int m_angle;

    float w[2];

    float h[2];

private slots:

    void valueChange(int value);

    void repaint();

private:

    Ui::MainWindow *ui;

};

#endif // MAINWINDOW_H

#include "mainwindow.h"

#include "ui_mainwindow.h"

#include <QTimer>

MainWindow::MainWindow(QWidget *parent) :

    QMainWindow(parent),

    ui(new Ui::MainWindow)

{

    ui->setupUi(this);

    ui->lineEdit->setText(QString("0")+QString("°   "));

    ui->lineEdit->setReadOnly(true);

    m_angle =0; //初始度

    QTimer *timer  = new QTimer(this);

    connect(timer,SIGNAL(timeout()),this,SLOT(repaint()));

    timer->start(1000);

    w[0] =300;  //初始宽度

    w[1] = w[0]; // w[1]和h[1]用于保存图片缩放前的宽和高

    h[0]= 300;

    h[1] =h[0];

    ui->horizontalSlider->setMaximum(360);

    connect(ui->horizontalSlider,SIGNAL(valueChanged(int)),this,SLOT(valueChange(int)));

}

MainWindow::~MainWindow()

{

    delete ui;

}

void MainWindow::valueChange(int value)

{

    ui->lineEdit->setText(QString::number(value)+ "° ");

    m_angle=value;

}

void MainWindow::repaint()

{

    w[0] =ui->graphicsView->width();

    pix1.load(":./11.jpg");

    pix2.load("");

    scene = new QGraphicsScene(this);

    scene->setSceneRect(0,0,300,300);

    ui->graphicsView->setScene(scene);

    ui->graphicsView->scale(w[0]/w[1],w[0]/w[1]);

    w[1]=w[0];

    h[1]=h[0];

    scene->setBackgroundBrush(pix1);

    pointer = new QGraphicsPixmapItem();

    pointer->setPixmap(pix2);

    pointer->setPos(150,150);

    scene->addItem(pointer);

    pointer->setRotation(360 -m_angle);

    QGraphicsTextItem *degree = new QGraphicsTextItem();

    degree->setPos(111,118);

    degree->setHtml(QString("<h2><font color  = red size =5>%1° </font></h2>").arg(m_angle));

    scene->addItem(degree);

}