QT 使用QPainter 绘制图形 和 世界变换 world transform

1. 绘制椭圆  饼状型 贝塞尔曲线

绘制图像重写方法 void paintEvent(QPaintEvent *event)即可。

void Widget::paintEvent(QPaintEvent *event)
{
    QPainter painter1(this);  //新建画笔
    painter1.setRenderHint(QPainter::Antialiasing, true);  //设置 反走样
    painter1.setPen(QPen(Qt::black, 8, Qt::DashDotLine, Qt::RoundCap));  //设置线条 颜色， 大小，线型风格，拐点风格
    painter1.setBrush(QBrush(Qt::green, Qt::SolidPattern));  //设置画刷 颜色 和 风格
    painter1.drawEllipse(10, 10, 160, 80);   //画椭圆

    QPainter painter2(this);
    painter2.setRenderHint(QPainter::Antialiasing, true);
    painter2.setPen(QPen(Qt::black, 8, Qt::DashDotLine, Qt::RoundCap));
    painter2.setBrush(QBrush(Qt::blue, Qt::DiagCrossPattern));
    painter2.drawPie(10, 150, 200, 120, 60*16, 270*16);

    QPainter painter3(this);
    painter3.setRenderHint(QPainter::Antialiasing, true);
    QPainterPath path;    //轨迹
    path.moveTo(200, 150);   //先移到这个点
    path.cubicTo(250, 80, 320, 80, 400, 150); //x1 x2 和 andpoint 确定弧形
    painter3.setPen(QPen(Qt::black, 8));
    painter3.setBrush(QBrush(Qt::green, Qt::DiagCrossPattern));

    QTransform transform;      //世界变换
    transform.translate(0, 0);  //以00为中心 选装30°
    transform.rotate(+30.0);
    painter3.setWorldTransform(transform);   //添加世界变换
    painter3.drawPath(path);
}

2. 仪表盘

oventimer.h

#ifndef OVENTIMER_H
#define OVENTIMER_H

#include <QWidget>
#include <QtGui>

class OvenTimer : public QWidget
{
    Q_OBJECT

public:
    OvenTimer(QWidget *parent = 0);

    void setDuration(int secs);
    int duration() const;
    void draw(QPainter *painter);

signals:
    void timeout();

protected:
    void paintEvent(QPaintEvent *event);
    void mousePressEvent(QMouseEvent *event);

private:
    QDateTime finishTime;
    QTimer *updateTimer;
    QTimer *finishTimer;
};

#endif // OVENTIMER_H

oventimer.cpp

#include "oventimer.h"
#include <QtGui>
#include <QtCore>
#include <math.h>

const double DegreesPerMinute = 7.0;
const double DegressPerSecond = DegreesPerMinute/60;
const int MaxMinutes = 45;
const int MaxSeconds = MaxMinutes*60;
const int UpdateInterval = 5;

OvenTimer::OvenTimer(QWidget *parent)
    : QWidget(parent)
{
    finishTime = QDateTime::currentDateTime();
    updateTimer = new QTimer(this);
    connect(updateTimer, SIGNAL(timeout()), this, SLOT(update()));

    finishTimer = new QTimer(this);
    finishTimer->setSingleShot(true);
    connect(finishTimer, SIGNAL(timeout()), this, SIGNAL(stop()));
    connect(finishTimer, SIGNAL(timeout()), updateTimer, SLOT(stop()));

    QFont font;
    font.setPointSize(8);
    setFont(font);
}

void OvenTimer::setDuration(int secs)
{
    secs = qBound(0, secs, MaxSeconds);
    finishTime = QDateTime::currentDateTime().addSecs(secs);
    if( secs > 0 )
    {
        updateTimer->start(UpdateInterval*1000);
        finishTimer->start(secs*1000);
    }
    else
    {
        updateTimer->stop();
        finishTimer->stop();
    }
    update();
}

int OvenTimer::duration() const
{
    int secs = QDateTime::currentDateTime().secsTo(finishTime);
    if( secs < 0 )
        secs = 0;
    return secs;
}

void OvenTimer::mousePressEvent(QMouseEvent *event)
{
    QPointF point = event->pos() - rect().center();
    double theta = atan2(-point.x(), -point.y())*180.0/M_PI;
    setDuration(duration() + int(theta / DegressPerSecond));
    update();
}

void OvenTimer::paintEvent(QPaintEvent *event)
{
    QPainter painter(this);
    painter.setRenderHint(QPainter::Antialiasing, true);
    int side = qMin(width(), height());
    painter.setViewport( (width()-side)/2, (height()-side)/2, side, side );
    painter.setWindow(-50, -50, 100, 100);
    draw(&painter);
}

void OvenTimer::draw(QPainter *painter)
{
    static const int triangle[3][2]={ {-2,-49}, {+2,-49}, {0,-47} };
    QPen thickPen(palette().foreground(), 1.5);
    QPen thinPen(palette().foreground(), 0.5);
    QColor niceBlue(150, 150, 200);

    painter->setPen(thinPen);
    painter->setBrush(palette().foreground());
    painter->drawPolygon( QPolygon(3, &triangle[0][0]) );

    QConicalGradient coneGradient(0,0,-90.0);
    coneGradient.setColorAt(0.0, Qt::darkGray);
    coneGradient.setColorAt(0.2, niceBlue);
    coneGradient.setColorAt(0.5, Qt::white);
    coneGradient.setColorAt(1.0, Qt::darkGray);
    painter->setBrush(coneGradient);
    painter->drawEllipse(-46, -46, 92, 92);

    QRadialGradient haloGradient(0,0,20,0,0);
    haloGradient.setColorAt(0.0, Qt::lightGray);
    haloGradient.setColorAt(0.8, Qt::darkGray);
    haloGradient.setColorAt(0.9, Qt::white);
    haloGradient.setColorAt(1.0, Qt::black);
    painter->setPen(Qt::NoPen);
    painter->setBrush(haloGradient);
    painter->drawEllipse(-20, -20, 40, 40);

    QLinearGradient knobGradient(-7, -25, 7, -25);
    knobGradient.setColorAt(0.0, Qt::black);
    knobGradient.setColorAt(0.2, niceBlue);
    knobGradient.setColorAt(0.3, Qt::lightGray);
    knobGradient.setColorAt(0.8, Qt::white);
    knobGradient.setColorAt(1.0, Qt::black);

    painter->rotate(duration() * DegressPerSecond);
    painter->setBrush(knobGradient);
    painter->setPen(thinPen);
    painter->drawRoundedRect(-7, -25, 14, 50, 99, 49);

    for( int i=0; i<=MaxMinutes; i++ )
    {
        if(i%5==0)
        {
            painter->setPen(thickPen);
            painter->drawLine(0, -41, 0, -44);
            painter->drawText(-15, -41, 30, 30,
                              Qt::AlignHCenter | Qt::AlignTop,QString::number(i));
        }
        else
        {
            painter->setPen(thinPen);
            painter->drawLine(0, -42, 0, -44);
        }
        painter->rotate(-DegreesPerMinute);
    }

}