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, 4): 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 = 0);
    ~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 = 0; i < POINTSNUM; ++i)
        {
            if (i % 2)
                vecData.append(rand() % 50 - 10);
            else
                vecData.append(rand() % 50 + 10);
        }
        double maxElement = *(std::max_element(vecData.begin(), vecData.end()));
        double minElement = *(std::min_element(vecData.begin(), vecData.end()));
        if (maxElement < 0)
        {
            maxScale = maxElement * LowerFactor;
            minScale = minElement * UpperFactor;
        }
        else if (0 == maxElement)
        {
            maxScale = 2;
            minScale = minElement * UpperFactor;
        }
        else if (maxElement > 0 && minElement < 0)
        {
            maxScale = maxElement * UpperFactor;
            minScale = minElement * UpperFactor;
        }
        else if (minElement > 0)
        {
            maxScale = maxElement * UpperFactor;
            minScale = minElement * LowerFactor;
        }

        scaleRange = maxScale - minScale;
    }
    void print()
    {
        for (int i = 0; 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(1000, 730); // 窗体大小 宽度1000 高度730

    m_image = QImage(990, 710, QImage::Format_RGB32);  // 画布的初始化大小设为，使用32位颜色
    QColor backColor = qRgb(255, 255, 255);    // 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(10, 10, 980 - 10, 700 - 10, Qt::white);
    Paint();
    update();
}

void MainWindow::Paint()
{
    // 确定坐标轴起点坐标
    int pointx = 80, pointy = 650;

    // 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 = 980 - pointx - 70;  // 宽度 = 画布宽度 - 坐标起点x - 右端间隙
    int height = 700 - 2 * 50;      // 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(20, 30, 980 - 10, 700 - 20);

    // 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(5);

    penPointY2.setColor(Qt::red);
    penPointY2.setWidth(5);

    for (int i = 0; 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(2);
    m_painter->setPen(penDegree);

    // x轴刻度线和值
    // x轴 第一个刻度值
    m_painter->drawText(pointx + 3, pointy + 12, QString::number(vectorX.minScale, 'f', 3));
    for (int i = 0; i < POINTSNUM - 1; ++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 + 12, // 值的位置信息
                         QString::number(vectorX.minScale + (i+1) * (vectorX.scaleRange/POINTSNUM), 'f', 3));
    }
    // x轴 最后一个刻度值
    m_painter->drawText(pointx + (POINTSNUM - 1 + 0.8) * width / POINTSNUM, pointy + 12,
                     QString::number(vectorX.maxScale, 'f', 3));

    xStartPoint.setX(pointx);
    xStartPoint.setY(pointy + 20);
    xEndPoint.setX(pointx + width);
    xEndPoint.setY(pointy + 20);
    m_painter->drawLine(xStartPoint, xEndPoint);

    m_painter->drawText(pointx + width/2, pointy + 35, QString("X"));

    // y1轴刻度线和值
    // y1轴 第一个刻度值
    m_painter->drawText(pointx - 25, pointy - 3, QString::number(vectorY1.minScale, 'f', 3));
    for (int i = 0; i < POINTSNUM - 1; ++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 - 25, pointy - (i+0.85) * height/POINTSNUM,
                         QString::number(vectorY1.minScale + (i+1) * (vectorY1.scaleRange/POINTSNUM), 'f', 3));
    }
    // y1轴 最后一个刻度值
    m_painter->drawText(pointx - 25, pointy - (POINTSNUM - 1 + 0.85) * height/POINTSNUM,
                     QString::number(vectorY1.maxScale, 'f', 3));

    y1StartPoint.setX(pointx - 35);
    y1StartPoint.setY(pointy - height);

    y1EndPoint.setX(pointx - 35);
    y1EndPoint.setY(pointy);
    m_painter->drawLine(y1StartPoint, y1EndPoint);

    m_painter->drawText(pointx - 55, pointy - height/2, QString("Y1"));

    // y2轴刻度线和值
    // y2轴 第一个刻度值
    m_painter->drawText(pointx + width + 10, pointy - 3, QString::number(vectorY2.minScale, 'f', 3));
    for (int i = 0; i < POINTSNUM - 1; ++i)
    {
//        m_painter->drawLine(pointx + width, pointy-(i+1)*height/10,
//                         pointx + width + 4, pointy-(i+1)*height/10);

        m_painter->drawText(pointx + width + 10, pointy - (i+0.85)*height/POINTSNUM,
                         QString::number((vectorY2.minScale + (i+1)*(vectorY2.scaleRange/POINTSNUM)), 'f' , 3));
    }
    // Y2轴 最后一个刻度值
    m_painter->drawText(pointx + width + 10, pointy - (POINTSNUM - 1 + 0.85)*height/POINTSNUM,
                     QString::number(vectorY2.maxScale, 'f', 3));

    y2StartPoint.setX(pointx + width + 40);
    y2StartPoint.setY(pointy - height);

    y2EndPoint.setX(pointx + width + 40);
    y2EndPoint.setY(pointy);
    m_painter->drawLine(y2StartPoint, y2EndPoint);

    m_painter->drawText(pointx + width + 50, pointy - height/2, QString("Y2"));

    // （5）绘制网格
    QPen penDotLine;
    penDotLine.setStyle(Qt::DotLine);
    m_painter->setPen(penDotLine);
    for (int i = 0; i < POINTSNUM; ++i)
    {
        // 垂直线
        m_painter->drawLine(pointx + (i+1)* width/POINTSNUM, pointy,
                         pointx + (i+1)* width/POINTSNUM, pointy - height);
        // 水平线
        m_painter->drawLine(pointx, pointy-(i+1)*height/POINTSNUM,
                         pointx + width, pointy-(i+1)*height/POINTSNUM);
    }
}

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

void MainWindow::paintEvent(QPaintEvent *)
{
    QPainter painter(this);
    painter.drawImage(0, 0, 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