利用QPainter绘制散点图

【1】实例代码

（1）代码目录结构（备注：QtCreator默认步骤新建工程）

（2）工程pro文件

 QT       += core gui
 
 greaterThan(QT_MAJOR_VERSION, ): QT += widgets
 
 TARGET = painter
 TEMPLATE = app
 
 SOURCES += main.cpp\
         mainwindow.cpp
 
 HEADERS  += mainwindow.h
 
 FORMS    += mainwindow.ui

（3）头文件

 #ifndef MAINWINDOW_H
 #define MAINWINDOW_H
 
 #include <QtGui>
 #include <QPaintEvent>
 #include <QMainWindow>
 
 #include <ctime>
 #include <cstdlib>
 
 namespace Ui
 {
     class MainWindow;
 }
 
 class MainWindow : public QMainWindow
 {
     Q_OBJECT
 
 public:
     explicit MainWindow(QWidget *parent = );
     ~MainWindow();
 
     void Paint();
 
 public slots:
     void onRefresh();
 protected:
     void paintEvent(QPaintEvent *);
 
 private:
     Ui::MainWindow *ui;
     QImage m_image;
     QPainter *m_painter;
 };
 
 #endif // MAINWINDOW_H

（4）实现文件

 #include "mainwindow.h"
 #include "ui_mainwindow.h"
 
 #define POINTSNUM 10
 #define LowerFactor 0.8
 #define UpperFactor 1.2
 
 typedef struct Data
 {
     double scaleRange;
     double maxScale;
     double minScale;
     QVector<double> vecData;
 
     Data() : scaleRange(0.0), maxScale(0.0), minScale(0.0)
     {}
     void init()
     {
         for (int i = ; i < POINTSNUM; ++i)
         {
             if (i % )
                 vecData.append(rand() %  - );
             else
                 vecData.append(rand() %  + );
         }
         double maxElement = *(std::max_element(vecData.begin(), vecData.end()));
         double minElement = *(std::min_element(vecData.begin(), vecData.end()));
         if (maxElement < )
         {
             maxScale = maxElement * LowerFactor;
             minScale = minElement * UpperFactor;
         }
         else if ( == maxElement)
         {
             maxScale = ;
             minScale = minElement * UpperFactor;
         }
         else if (maxElement >  && minElement < )
         {
             maxScale = maxElement * UpperFactor;
             minScale = minElement * UpperFactor;
         }
         else if (minElement > )
         {
             maxScale = maxElement * UpperFactor;
             minScale = minElement * LowerFactor;
         }
 
         scaleRange = maxScale - minScale;
     }
     void print()
     {
         for (int i = ; i < POINTSNUM; ++i)
         {
             qDebug () << i << "::" << vecData[i] << " ";
         }
         qDebug() << endl;
     }
 }DataInfo;
 
 MainWindow::MainWindow(QWidget *parent)
     : QMainWindow(parent),
       ui(new Ui::MainWindow)
 {
     ui->setupUi(this);
     ui->mainToolBar->setVisible(true);
 
     QAction *pAction = new QAction("refresh", this);
     ui->mainToolBar->addAction(pAction);
     connect(pAction, &QAction::triggered, this, &MainWindow::onRefresh);
 
     resize(, ); // 窗体大小 宽度1000 高度730
 
     m_image = QImage(, , QImage::Format_RGB32);  // 画布的初始化大小设为，使用32位颜色
     QColor backColor = qRgb(, , );    // 画布初始化背景色使用白色
     m_image.fill(backColor); // 对画布进行填充
 
     m_painter = new QPainter(&m_image);
     m_painter->setRenderHint(QPainter::Antialiasing, true); // 设置反锯齿模式
 
     Paint();
 }
 
 void MainWindow::onRefresh()
 {
     m_painter->fillRect(, ,  - ,  - , Qt::white);
     Paint();
     update();
 }
 
 void MainWindow::Paint()
 {
     // 确定坐标轴起点坐标
     int pointx = , pointy = ;
 
     // 确定坐标轴宽度和高度，上文已定义画布大小，宽高依此而定。
     int width =  - pointx - ;  // 宽度 = 画布宽度 - 坐标起点x - 右端间隙
     int height =  -  * ;      // 高度 = 画布高度 - 上下端的间隙高度
 
     // 绘制视图区域
     // 即外围的矩形（由左上角与右下角的两个点确定一个矩形）
     m_painter->drawRect(, ,  - ,  - );
 
     // 绘制X、Y1、Y2轴
     QPointF xStartPoint(pointx, pointy);
     QPointF xEndPoint(width + pointx, pointy);
     m_painter->drawLine(xStartPoint, xEndPoint); // 坐标轴x宽度为width
 
     QPointF y1StartPoint(pointx, pointy - height);
     QPointF y1EndPoint(pointx, pointy);
     m_painter->drawLine(y1StartPoint, y1EndPoint); // 坐标轴y1高度为height
 
     QPointF y2StartPoint(pointx + width, pointy - height);
     QPointF y2EndPoint(pointx + width, pointy);
     m_painter->drawLine(y2StartPoint, y2EndPoint); // 坐标轴y2高度为height
 
     // （2）获得数据并分析最大值与最小值
     DataInfo vectorX, vectorY1, vectorY2; // 数据储存在容器中，大小为POINTSNUM]
     // 模拟随机数据
     srand((int)time(NULL));
     vectorX.init();
     vectorY1.init();
     vectorY2.init();
 
     vectorX.print();
     vectorY1.print();
     vectorY2.print();
 
     double kx = (double)(width / vectorX.scaleRange); // x轴的系数
     double ky1 = (double)(height / vectorY1.scaleRange);  // y1方向的比例系数
     double ky2 = (double)(height / vectorY2.scaleRange);  // y2方向的比例系数
 
     // （3）绘制点
     QPen penPointY1, penPointY2;
     penPointY1.setColor(Qt::blue);
     penPointY1.setWidth();
 
     penPointY2.setColor(Qt::red);
     penPointY2.setWidth();
 
     for (int i = ; i < POINTSNUM; ++i)
     {
         double dXStart = pointx + kx * (vectorX.vecData[i] - vectorX.minScale);
         m_painter->setPen(penPointY1); // 蓝色的笔，用于标记Y1各个点
         m_painter->drawPoint(dXStart, pointy - (vectorY1.vecData[i] - vectorY1.minScale) * ky1);
 
         m_painter->setPen(penPointY2); // 红色的笔，用于标记Y2各个点
         m_painter->drawPoint(dXStart, pointy - (vectorY2.vecData[i] - vectorY2.minScale) * ky2);
     }
 
     // （4） 绘制刻度线
     QPen penDegree;
     penDegree.setColor(Qt::black);
     penDegree.setWidth();
     m_painter->setPen(penDegree);
 
     // x轴刻度线和值
     // x轴 第一个刻度值
     m_painter->drawText(pointx + , pointy + , QString::number(vectorX.minScale, 'f', ));
     for (int i = ; i < POINTSNUM - ; ++i) // 分成10份
     {
 //        // 选取合适的坐标，绘制一段长度为4的直线，用于表示刻度
 //        m_painter->drawLine(pointx + (i + 1) * width/10, pointy,
 //                         pointx + (i+1)*width/10, pointy + 4);
 
         m_painter->drawText(pointx + (i+0.9) * width / POINTSNUM, pointy + , // 值的位置信息
                          QString::number(vectorX.minScale + (i+) * (vectorX.scaleRange/POINTSNUM), 'f', ));
     }
     // x轴 最后一个刻度值
     m_painter->drawText(pointx + (POINTSNUM -  + 0.8) * width / POINTSNUM, pointy + ,
                      QString::number(vectorX.maxScale, 'f', ));
 
     xStartPoint.setX(pointx);
     xStartPoint.setY(pointy + );
     xEndPoint.setX(pointx + width);
     xEndPoint.setY(pointy + );
     m_painter->drawLine(xStartPoint, xEndPoint);
 
     m_painter->drawText(pointx + width/, pointy + , QString("X"));
 
     // y1轴刻度线和值
     // y1轴 第一个刻度值
     m_painter->drawText(pointx - , pointy - , QString::number(vectorY1.minScale, 'f', ));
     for (int i = ; i < POINTSNUM - ; ++i)
     {
         // 代码较长，但是掌握基本原理即可。
         // 主要就是确定一个位置，然后画一条短短的直线表示刻度。
 
 //        m_painter->drawLine(pointx, pointy-(i+1)*height/10,
 //                         pointx-4, pointy-(i+1)*height/10);
 
         m_painter->drawText(pointx - , pointy - (i+0.85) * height/POINTSNUM,
                          QString::number(vectorY1.minScale + (i+) * (vectorY1.scaleRange/POINTSNUM), 'f', ));
     }
     // y1轴 最后一个刻度值
     m_painter->drawText(pointx - , pointy - (POINTSNUM -  + 0.85) * height/POINTSNUM,
                      QString::number(vectorY1.maxScale, 'f', ));
 
     y1StartPoint.setX(pointx - );
     y1StartPoint.setY(pointy - height);
 
     y1EndPoint.setX(pointx - );
     y1EndPoint.setY(pointy);
     m_painter->drawLine(y1StartPoint, y1EndPoint);
 
     m_painter->drawText(pointx - , pointy - height/, QString("Y1"));
 
     // y2轴刻度线和值
     // y2轴 第一个刻度值
     m_painter->drawText(pointx + width + , pointy - , QString::number(vectorY2.minScale, 'f', ));
     for (int i = ; i < POINTSNUM - ; ++i)
     {
 //        m_painter->drawLine(pointx + width, pointy-(i+1)*height/10,
 //                         pointx + width + 4, pointy-(i+1)*height/10);
 
         m_painter->drawText(pointx + width + , pointy - (i+0.85)*height/POINTSNUM,
                          QString::number((vectorY2.minScale + (i+)*(vectorY2.scaleRange/POINTSNUM)), 'f' , ));
     }
     // Y2轴 最后一个刻度值
     m_painter->drawText(pointx + width + , pointy - (POINTSNUM -  + 0.85)*height/POINTSNUM,
                      QString::number(vectorY2.maxScale, 'f', ));
 
     y2StartPoint.setX(pointx + width + );
     y2StartPoint.setY(pointy - height);
 
     y2EndPoint.setX(pointx + width + );
     y2EndPoint.setY(pointy);
     m_painter->drawLine(y2StartPoint, y2EndPoint);
 
     m_painter->drawText(pointx + width + , pointy - height/, QString("Y2"));
 
     // （5）绘制网格
     QPen penDotLine;
     penDotLine.setStyle(Qt::DotLine);
     m_painter->setPen(penDotLine);
     for (int i = ; i < POINTSNUM; ++i)
     {
         // 垂直线
         m_painter->drawLine(pointx + (i+)* width/POINTSNUM, pointy,
                          pointx + (i+)* width/POINTSNUM, pointy - height);
         // 水平线
         m_painter->drawLine(pointx, pointy-(i+)*height/POINTSNUM,
                          pointx + width, pointy-(i+)*height/POINTSNUM);
     }
 }
 
 MainWindow::~MainWindow()
 {
     delete ui;
     delete m_painter;
 }
 
 void MainWindow::paintEvent(QPaintEvent *)
 {
     QPainter painter(this);
     painter.drawImage(, , m_image);
 }

（5）main文件

 #include "mainwindow.h"
 #include <QApplication>
 
 int main(int argc, char *argv[])
 {
     QApplication a(argc, argv);
     MainWindow w;
     w.show();
 
     return a.exec();
 }

【2】效果图

运行结果图如下：

Good Good Study, Day Day Up.

顺序 选择 循环 总结