用Qt实现2D绘图

•  新建Gui应用程序，基类选择QWidget

•  widget.h代码：   

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>

namespace Ui {
class Widget;
}

class Widget : public QWidget
{
    Q_OBJECT
    
public:
    explicit Widget(QWidget *parent = 0);
    ~Widget();
    
private:
    Ui::Widget *ui;
protected:
    void paintEvent(QPaintEvent *event);
};

#endif // WIDGET_H linux

• widget.cpp代码

#include "widget.h"
#include "ui_widget.h"
#include <QPainter>
Widget::Widget(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::Widget)
{
    ui->setupUi(this);
}
void Widget::paintEvent(QPaintEvent *event)
{
    QPainter painter(this);
    painter.drawLine(QPoint(0,0),QPoint(100,100));
    //建立画笔
    QPen pen(Qt::green,5,Qt::DotLine,Qt::RoundCap,Qt::RoundJoin);
    painter.setPen(pen);
    QRectF rectangle(70.0,40.0,80.0,60.0);
    int startAngle=30*16;
    int spanAngle=120*16;
    painter.drawArc(rectangle,startAngle,spanAngle);
    pen.setWidth(1);
    pen.setStyle(Qt::SolidLine);
    painter.setPen(pen);
    //绘制一个矩形
    painter.drawRect(160,20,50,40);
    //建立画刷
    QBrush brush(QColor(0,0,255),Qt::Dense4Pattern);
    //使用画刷
    painter.setBrush(brush);
    //绘制画刷
    painter.drawEllipse(220,20,50,50);
    //设置纹理
    brush.setTexture(QPixmap("yafeilinux.png"));
    //从新使用画刷
    painter.setBrush(brush);
    //定义四个点
    static const QPointF points[4]={
        QPointF(270.0,80.0),
        QPointF(290.0,10),
        QPointF(350.0,30),
        QPointF(390.0,50)


    };
    painter.drawPolygon(points,4);
    painter.fillRect(QRect(10,100,150,20),QBrush(Qt::darkYellow));
    painter.eraseRect(QRect(50,0,50,120));
    //线性渐变
    QLinearGradient linearGradient(QPointF(40,190),QPointF(70,190));

    //插入颜色
    linearGradient.setColorAt(0,Qt::yellow);
    linearGradient.setColorAt(0.5,Qt::red);
    linearGradient.setColorAt(1.0,Qt::green);

    //指定渐变区域之外的区域的扩散方式
    linearGradient.setSpread(QGradient::RepeatSpread);
    //使用渐变做为画刷
    painter.setBrush(linearGradient);
    painter.drawRect(10,170,90,40);
    //辐射渐变
    QRadialGradient radialGradient(QPointF(200,190),50,QPointF(275,200));
    radialGradient.setColorAt(0,QColor(255,255,100,150));
    radialGradient.setColorAt(1,QColor(0,0,0,50));
    painter.setBrush(radialGradient);
    painter.drawEllipse(QPointF(200,190),50,50);

    //锥形渐变
    QConicalGradient conicalGradient(QPointF(350,190),60);
    conicalGradient.setColorAt(0.2,Qt::cyan);
    conicalGradient.setColorAt(0.9,Qt::black);
    painter.setBrush(conicalGradient);
    painter.drawEllipse(QPointF(350,190),50,50);
    //画笔使用线性渐变来绘制直线和文字
    painter.setPen(QPen(linearGradient,2));
    painter.drawLine(0,280,100,280);
    painter.drawText(150,280,tr("helloQt"));
}
Widget::~Widget()
{
    delete ui;
}

• 运行结果：