#ifndef SPEEDMETERWIDGET_H#define SPEEDMETERWIDGET_H#include<QWidget>#include<QPainter>#include<QRadialGradient>#include<QFont>#include<QFontDatabase>#include<QPointF>#include<QRectF>class SpeedMeterWidget : public QWidget{    Q_OBJECTpublic:    explicitSpeedMeterWidget(QWidget *parent = nullptr);    voidsetCurrentValue(int val);protected:    voidpaintEvent(QPaintEvent *event)override;private:    int m_maxValue = 260;    int m_minValue = 0;    int m_currentValue = 130;    int m_redValue = 200;    QColor m_bgColor;    QFont m_digitFont;};#endif// SPEEDMETERWIDGET_H

#include "SpeedMeterWidget.h"#include <cmath>#include <QFontMetricsF>SpeedMeterWidget::SpeedMeterWidget(QWidget *parent)    : QWidget(parent),    m_bgColor(QColor("#00020414")){    // 加载外部数字字体 Digitall.ttf，资源文件里注册    int fontId = QFontDatabase::addApplicationFont(":/font/image/Digitall.ttf");    if(fontId != -1)    {        QString family = QFontDatabase::applicationFontFamilies(fontId).first();        m_digitFont = QFont(family);    }    else    {        // 兜底字体        m_digitFont = QFont("Arial", 40);    }}void SpeedMeterWidget::setCurrentValue(int val){    m_currentValue = val;    update(); // 触发重绘}void SpeedMeterWidget::paintEvent(QPaintEvent *event){    QWidget::paintEvent(event);    QPainter painter(this);    painter.setRenderHint(QPainter::Antialiasing);    int w = width();    int h = height();    qreal centerX = w / 2.0;    qreal centerY = h / 2.0;    qreal radius = qMin(w, h) / 2.0 * 0.9;    // 1. 背景填充    painter.fillRect(0, 0, w, h, m_bgColor);    // 2. 内层红色径向渐变圆环    QRadialGradient radialGrad(centerX, centerY, radius * 0.6);    QColor colCenter("#E43223");    QColor colEdge("#00E43223");    radialGrad.setColorAt(0, colCenter);    radialGrad.setColorAt(1, colEdge);    painter.setBrush(radialGrad);    painter.setPen(Qt::NoPen);    painter.drawEllipse(QPointF(centerX, centerY), radius * 0.6, radius * 0.6);    // 3. 中间黑色内圆    painter.setBrush(Qt::black);    painter.drawEllipse(QPointF(centerX, centerY), radius * 0.5, radius * 0.5);    // ====================== 绘制刻度线 ======================    painter.save();    const int startAngle = 45;    qreal r = radius;    const int totalSteps = 130;    qreal rotateStep = (360.0 - startAngle * 2) / totalSteps;    painter.translate(centerX, centerY);    painter.rotate(startAngle);    for(int i = 0; i <= totalSteps; ++i)    {        int val = i * 2;        QColor bigColor, smallColor;        if(val >= m_redValue)        {            bigColor = Qt::red;            smallColor = Qt::red;        }        else        {            bigColor = QColor("#B6C6D6");            smallColor = QColor("#525B62");        }        QPen pen;        pen.setCapStyle(Qt::RoundCap);        if(i % 10 == 0)        {            pen.setColor(bigColor);            pen.setWidth(9);            painter.setPen(pen);            painter.drawLine(QPointF(0, r), QPointF(0, r / 1.1));        }        else if (i % 5 == 0)        {            pen.setColor(smallColor);            pen.setWidth(8);            painter.setPen(pen);            painter.drawLine(QPointF(0, r), QPointF(0, r / 1.08));        }        else        {            pen.setColor(smallColor);            pen.setWidth(6);            painter.setPen(pen);            painter.drawLine(QPointF(0, r), QPointF(0, r / 1.05));        }        painter.rotate(rotateStep);    }    painter.restore();    // ====================== 外圈刻度数字 ======================    painter.save();    qreal numR = radius * 0.75;    qreal numGapAngle = (360.0 - startAngle * 2) / 13.0;    qreal valStep = (m_maxValue - m_minValue) / 13.0;    qreal currentDrawVal = m_minValue;    int startDeg = startAngle;    QFont numFont = m_digitFont;    numFont.setPointSizeF(w * 0.04);    painter.setFont(numFont);    QFontMetricsF fm(numFont);    for(int i = 0; i < 14; ++i)    {        if(currentDrawVal >= m_redValue)            painter.setPen(Qt::red);        else            painter.setPen(Qt::white);        qreal angleDeg = -90.0 + startDeg + numGapAngle * i;        qreal rad = qDegreesToRadians(angleDeg);        qreal x = -numR * cos(rad);        qreal y = -numR * sin(rad);        painter.save();        painter.translate(centerX + x, centerY + y);        QString text = QString::number(qRound(currentDrawVal));        qreal textW = fm.horizontalAdvance(text);        qreal textH = w * 0.06;        qreal offsetY = textH / 4.0;        painter.drawText(QPointF(-textW / 2.0, offsetY), text);        painter.restore();        currentDrawVal += valStep;    }    painter.restore();    // ====================== 指针绘制 ======================    painter.save();    qreal degRotate = (270.0 / (m_maxValue - m_minValue)) * (m_currentValue - m_minValue) + 135.0;    painter.translate(centerX, centerY);    painter.rotate(degRotate);    QPen pen;    pen.setColor(Qt::white);    pen.setWidth(8);    pen.setCapStyle(Qt::RoundCap);    painter.setPen(pen);    painter.drawLine(QPointF(radius * 0.5, 0), QPointF(radius * 0.9, 0));    painter.restore();    // ====================== 中心三位数字 + KM/h ======================    painter.save();    painter.setPen(Qt::white);    // 大数字字体    qreal numFontSize = w * 0.12;    QFont bigFont = m_digitFont;    bigFont.setPointSizeF(numFontSize);    painter.setFont(bigFont);    QFontMetricsF fmBig(bigFont);    int val = m_currentValue;    int hundred = val / 100;    int ten = (val / 10) % 10;    int unit = val % 10;    qreal singleW = fmBig.horizontalAdvance("0");    qreal gap = singleW * 0.001;    qreal totalWidth = singleW * 3 + gap * 2;    qreal startX = centerX - totalWidth / 2.0;    // 百位    if(hundred == 0)        painter.setPen(QColor("#666666"));    else        painter.setPen(Qt::white);    painter.drawText(QPointF(startX, centerY), QString::number(hundred));    // 十位    qreal tenX = startX + singleW + gap;    if(ten == 0 && hundred == 0)        painter.setPen(QColor("#666666"));    else        painter.setPen(Qt::white);    painter.drawText(QPointF(tenX, centerY), QString::number(ten));    // 个位    qreal unitX = tenX + singleW + gap;    if(unit == 0 && hundred == 0 && ten == 0)        painter.setPen(QColor("#666666"));    else        painter.setPen(Qt::white);    painter.drawText(QPointF(unitX, centerY), QString::number(unit));    // KM/h 下方文字    QFont unitFont = m_digitFont;    unitFont.setPointSizeF(w * 0.05);    painter.setFont(unitFont);    QRectF rectUnit(0, centerY + 50, w, h);    painter.drawText(rectUnit, Qt::AlignHCenter, "KM/h");    painter.restore();}

#include"mainwindow.h"#include<QDebug>#include<QWidget>#include<QVBoxLayout>#include<QSlider>#include"speedmeterwidget.h"MainWindow::MainWindow(QWidget *parent)    : QMainWindow(parent){    this->resize(800, 800);    QWidget *central = new QWidget(this);    central->setStyleSheet("background-color: #020414;");    this->setCentralWidget(central);    QVBoxLayout *lay = new QVBoxLayout(central);    lay->setContentsMargins(0, 0, 0, 20);    SpeedMeterWidget *meter = new SpeedMeterWidget();    lay->addWidget(meter);    QSlider *slider = new QSlider(Qt::Horizontal);    slider->setRange(0, 260);    slider->setValue(130);    lay->addWidget(slider);    // 滑块联动更新数值    QObject::connect(slider, &QSlider::valueChanged, meter, &SpeedMeterWidget::setCurrentValue);}MainWindow::~MainWindow(){}

https://download.csdn.net/download/qq_15181569/93203495

// 创建 QPainter 对象QPainter painter(this);  // 在 QWidget 上绘图painter.setRenderHint(QPainter::Antialiasing);  // 开启抗锯齿

// 坐标变换painter.translate(100, 100);    // 平移坐标系painter.rotate(45);             // 旋转坐标系painter.scale(2.0, 2.0);        // 缩放坐标系painter.shear(0.5, 0);          // 错切变换

// 绘制线条painter.drawLine(QPointF(0, 0), QPointF(100, 100));// 绘制矩形painter.drawRect(QRectF(10, 10, 100, 50));// 绘制椭圆/圆形painter.drawEllipse(QPointF(50, 50), 30, 30);// 绘制多边形QPolygonF polygon;polygon << QPointF(0, 0) << QPointF(50, 0) << QPointF(25, 50);painter.drawPolygon(polygon);

// 设置字体QFont font("Arial", 12, QFont::Bold);painter.setFont(font);// 绘制文本painter.drawText(QPointF(10, 30), "Hello Qt6!");painter.drawText(QRectF(10, 50, 200, 50), Qt::AlignCenter, "居中文本");

QPixmap pixmap(":/images/logo.png");painter.drawPixmap(10, 10, pixmap);

QPen pen;pen.setColor(Qt::red);           // 设置颜色pen.setWidth(3);                 // 设置线宽pen.setStyle(Qt::DashLine);      // 设置线型pen.setCapStyle(Qt::RoundCap);   // 设置端点样式pen.setJoinStyle(Qt::RoundJoin); // 设置连接样式painter.setPen(pen);

QBrush brush;brush.setColor(Qt::blue);                // 纯色填充brush.setStyle(Qt::SolidPattern);        // 填充样式// 渐变填充QLinearGradient gradient(0, 0, 100, 100);gradient.setColorAt(0, Qt::white);gradient.setColorAt(1, Qt::black);brush = QBrush(gradient);painter.setBrush(brush);

painter.setRenderHint(QPainter::Antialiasing);        // 开启抗锯齿painter.setRenderHint(QPainter::TextAntialiasing);    // 文本抗锯齿painter.setRenderHint(QPainter::SmoothPixmapTransform); // 平滑图像变换

// 设置合成模式painter.setCompositionMode(QPainter::CompositionMode_SourceOver);  // 默认：源覆盖目标painter.setCompositionMode(QPainter::CompositionMode_SourceIn);    // 源在目标内部painter.setCompositionMode(QPainter::CompositionMode_Xor);         // 异或模式

// 设置裁剪区域QPainterPath clipPath;clipPath.addEllipse(50, 50, 100, 100);painter.setClipPath(clipPath);// 恢复裁剪painter.setClipping(false);

// 保存当前绘图状态painter.save();// 平移坐标系到圆心painter.translate(centerX, centerY);// 旋转坐标系绘制刻度线painter.rotate(startAngle);for (int i = 0; i <= totalSteps; ++i) {    painter.drawLine(...);    painter.rotate(rotateStep);}// 恢复绘图状态painter.restore();

// 创建径向渐变QRadialGradient radialGrad(centerX, centerY, radius * 0.6);radialGrad.setColorAt(0, QColor("#E43223"));  // 中心颜色radialGrad.setColorAt(1, QColor("#00E43223")); // 边缘颜色（透明）painter.setBrush(radialGrad);painter.drawEllipse(QPointF(centerX, centerY), radius * 0.6, radius * 0.6);

// 计算文本宽度进行居中QFontMetricsF fm(numFont);QString text = QString::number(qRound(currentDrawVal));qreal textW = fm.horizontalAdvance(text);painter.drawText(QPointF(-textW / 2.0, offsetY), text);