#include <QPainter>
#include <QWidget>
#include <QApplication>
class Thermometer : public QWidget {
public:
    Thermometer(QWidget *parent = 0);
protected:
    void paintEvent(QPaintEvent *event);
private:
    int value;
};
Thermometer::Thermometer(QWidget *parent)
    : QWidget(parent), value(50) {}
void Thermometer::paintEvent(QPaintEvent * /* event */) {
    QPainter painter(this);
    painter.setRenderHint(QPainter::Antialiasing);
    painter.setPen(Qt::NoPen);
    // 繪制溫度計(jì)背景
    painter.setBrush(QColor("#f0f0f0"));
    painter.drawRect(0, 0, width(), height());
    // 繪制溫度計(jì)外框
    painter.setBrush(QColor("#f5f5f5"));
    painter.drawRect(20, 20, width() - 40, height() - 40);
    // 繪制溫度計(jì)刻度線
    painter.setPen(QColor("#999999"));
    for (int i = 0; i <= 100; i += 10) {
        painter.drawLine(40, height() - 40 - (i * (height() - 80) / 100),
                         60, height() - 40 - (i * (height() - 80) / 100));
    }
    // 繪制溫度計(jì)當(dāng)前溫度
    painter.setPen(QColor("#ff0000"));
    painter.setFont(QFont("Arial", 14));
    painter.drawText(80, height() , QString::number(value) + ".");
    // 繪制溫度計(jì)水銀柱
    painter.setBrush(QColor("#ff0000"));
    painter.drawRect(30, height() - 40 - (value * (height() - 80) / 100),
                     width() - 60, value * (height() - 80) / 100);
}
int main(int argc, char *argv[]) {
    QApplication app(argc, argv);
    Thermometer thermometer;
    thermometer.setWindowTitle("thermometer");
    thermometer.resize(200, 400);
    thermometer.show();
    return app.exec();
}

QLabel *tempLabel = new QLabel(this);
tempLabel->setText("Temp: 0℃");
tempLabel->setGeometry(20, 20, 100, 20);

QGraphicsView *view = new QGraphicsView(this);
view->setGeometry(20, 50, 200, 200);

QGraphicsScene *scene = new QGraphicsScene(this);
view->setScene(scene);

QGraphicsRectItem *frame = new QGraphicsRectItem(0, 0, 200, 200);
frame->setPen(QPen(Qt::black));
frame->setBrush(QBrush(Qt::white));
scene->addItem(frame);

QGraphicsEllipseItem *center = new QGraphicsEllipseItem(90, 90, 20, 20);
center->setPen(QPen(Qt::black));
center->setBrush(QBrush(Qt::black));
scene->addItem(center);

for (int i = -45; i <= 225; i += 45) {
    QLineF line(100 + 80 * cos(i * M_PI / 180),
                100 - 80 * sin(i * M_PI / 180),
                100 + 100 * cos(i * M_PI / 180),
                100 - 100 * sin(i * M_PI / 180));
    QGraphicsLineItem *tick = new QGraphicsLineItem(line);
    tick->setPen(QPen(Qt::black));
    scene->addItem(tick);
}

QPointF points[3] = { QPointF(100, 100),
                      QPointF(95, 90),
                      QPointF(105, 90) };
QGraphicsPolygonItem *pointer = new QGraphicsPolygonItem(QPolygonF(points, 3));
pointer->setPen(QPen(Qt::black));
pointer->setBrush(QBrush(Qt::red));
pointer->setTransformOriginPoint(100, 100);
scene->addItem(pointer);

QGraphicsTransform *pointerTransform;

pointerTransform = new QGraphicsTransform(pointer);
pointer->setTransform(pointerTransform);

void MainWindow::updateTemp(int temp) {
    ui->tempLabel->setText(QString("Temp: %1℃").arg(temp));
    pointerTransform->setRotation(-45 + temp * 270 / 100);
}

signals:
    void tempChanged(int temp);

connect(this, SIGNAL(tempChanged(int)), this, SLOT(updateTemp(int)));

void MainWindow::on_tempSlider_valueChanged(int value)
{
    emit tempChanged(value);
}

connect(ui->tempSlider, SIGNAL(valueChanged(int)), this, SLOT(on_tempSlider_valueChanged(int)));