Qt使用cos、sin绘制圆

实例：

.pro

QT       += core gui

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

CONFIG += c++17

# The following define makes your compiler emit warnings if you use
# any Qt feature that has been marked deprecated (the exact warnings
# depend on your compiler). Please consult the documentation of the
# deprecated API in order to know how to port your code away from it.
DEFINES += QT_DEPRECATED_WARNINGS

# You can also make your code fail to compile if it uses deprecated APIs.
# In order to do so, uncomment the following line.
# You can also select to disable deprecated APIs only up to a certain version of Qt.
#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.0

SOURCES += 
    main.cpp 
    mainwindow.cpp

HEADERS += 
    mainwindow.h

FORMS += 
    mainwindow.ui

# Default rules for deployment.
qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += target

RESOURCES += 
    resource.qrc

main.cpp

#include "mainwindow.h"

#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
    return a.exec();
}

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QPainter>
#include <QDebug>
#include <QtWidgets/QLabel>
#include <QtWidgets/QLineEdit>
#include <QtWidgets/QMainWindow>
#include <QtWidgets/QMenuBar>
#include <QtWidgets/QSlider>
#include <QtWidgets/QStatusBar>
#include <QtWidgets/QWidget>
#include <QtMath>

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();
    void paintEvent(QPaintEvent *e);
private slots:
    void on_horizontalSlider_valueChanged(int value);

    void on_horizontalSlider_2_valueChanged(int value);

private:
    Ui::MainWindow *ui;
    int m_y = 0;//
    int m_l = 100;//
    int m_nSize = 200;
    QPoint m_oCentre;
    int m_nCentreWidth = 6;// 中心点宽度
};
#endif // MAINWINDOW_H

mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    setWindowTitle(QStringLiteral("Qt使用cos、sin绘制圆"));
}

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

void MainWindow::paintEvent(QPaintEvent *e)
{
    m_oCentre.setX((m_nSize/2));
    m_oCentre.setY((m_nSize/2));

    int nDeviation = 0;
    // 生成绘制
    QPainter oLinePainter(this);
    oLinePainter.setWindow(nDeviation, nDeviation, this->width(), this->height());
    // 背景
    QBrush objBrush(Qt::yellow, Qt::SolidPattern);
    oLinePainter.fillRect(0, 0, m_nSize, m_nSize, objBrush);
    // ---------------------画中心点--------------------------
    QPainter oCentrePainter(this);
    oCentrePainter.setWindow(nDeviation, nDeviation, this->width(), this->height());
    QPen oCentrePen;
    oCentrePen.setColor(Qt::red);
    oCentrePen.setWidth(1);
    oCentrePen.setStyle(Qt::SolidLine);
    oCentrePainter.setPen(oCentrePen);

    QBrush oCentreBrush(QColor(255,0,0), Qt::SolidPattern);
    oCentrePainter.setBrush(oCentreBrush);

    QPainterPath oCentreDrawPath;

    oCentreDrawPath.addRect(m_oCentre.x(),
                            m_oCentre.y(),
                            m_nCentreWidth,
                            m_nCentreWidth);
    //
    oCentrePainter.drawPath(oCentreDrawPath);
    // ---------------------画中心点--------------------------
    float x = 0;
    float y = 0;
    float fPI = 3.14159265358979323;
    x = sin(m_y*fPI/180)*m_l + m_oCentre.x();
    y = -cos(m_y*fPI/180)*m_l + m_oCentre.x();


    QPainter oPainter(this);
    oCentrePainter.setWindow(nDeviation, nDeviation, this->width(), this->height());
    QPen oPen;
    oPen.setColor(Qt::blue);
    oPen.setWidth(1);
    oPen.setStyle(Qt::SolidLine);
    oPainter.setPen(oPen);

    QBrush oBrush(QColor(255,0,0), Qt::SolidPattern);
    oPainter.setBrush(oBrush);

    QPainterPath oDrawPath;

    oDrawPath.addRect(x,
                      y,
                      m_nCentreWidth,
                      m_nCentreWidth);
    //
    oPainter.drawPath(oDrawPath);
}

void MainWindow::on_horizontalSlider_valueChanged(int value)
{
    ui->label->setText(QString::number(value));
    m_y = value;
    this->repaint();
}

void MainWindow::on_horizontalSlider_2_valueChanged(int value)
{
    ui->label_2->setText(QString::number(value));
    m_l = value;
    this->repaint();
}

mainwindow.ui

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
 <class>MainWindow</class>
 <widget class="QMainWindow" name="MainWindow">
  <property name="geometry">
   <rect>
    <x>0</x>
    <y>0</y>
    <width>678</width>
    <height>234</height>
   </rect>
  </property>
  <property name="windowTitle">
   <string>MainWindow</string>
  </property>
  <widget class="QWidget" name="centralwidget">
   <widget class="QSlider" name="horizontalSlider">
    <property name="geometry">
     <rect>
      <x>260</x>
      <y>20</y>
      <width>341</width>
      <height>22</height>
     </rect>
    </property>
    <property name="maximum">
     <number>360</number>
    </property>
    <property name="orientation">
     <enum>Qt::Horizontal</enum>
    </property>
   </widget>
   <widget class="QLabel" name="label">
    <property name="geometry">
     <rect>
      <x>620</x>
      <y>20</y>
      <width>54</width>
      <height>12</height>
     </rect>
    </property>
    <property name="text">
     <string>TextLabel</string>
    </property>
   </widget>
   <widget class="QLabel" name="label_2">
    <property name="geometry">
     <rect>
      <x>620</x>
      <y>60</y>
      <width>54</width>
      <height>12</height>
     </rect>
    </property>
    <property name="text">
     <string>TextLabel</string>
    </property>
   </widget>
   <widget class="QSlider" name="horizontalSlider_2">
    <property name="geometry">
     <rect>
      <x>260</x>
      <y>60</y>
      <width>341</width>
      <height>22</height>
     </rect>
    </property>
    <property name="maximum">
     <number>150</number>
    </property>
    <property name="value">
     <number>100</number>
    </property>
    <property name="orientation">
     <enum>Qt::Horizontal</enum>
    </property>
   </widget>
  </widget>
 </widget>
 <resources/>
 <connections/>
</ui>