QT绘画

QT绘画 QPainter

• 重载 paintEvent

  1. 准备画笔

      QPainter p(this);
     
          p.setPen(QPen(Qt::red, 2, Qt::DashLine));
          p.setBrush(Qt::yellow); //  背景颜色
          p.setFont(QFont("aaa", 40, 700, true)); //italic

  2. 绘制形状

      p.drawLine(QPoint(0,0), QPoint(100,100));
      p.drawRect(QRect(40,60,100,50));
      p.drawText(QPoint(300, 50), "Hellow");
      p.drawPixmap(QPoint(40,40), QPixmap("../aaa.png"));

  3. 图形变换

      {
          QTransform transfrom;       //  可将复杂的功能组合
          transfrom.rotate(30);
          transfrom.scale(.5,.5);     //  缩放
          p.setTransform(transfrom);  //  旋转
      }
     
      p.translate(100,100);   //  变换原点坐标单独

  4. 消除锯齿

      p.setRenderHint(QPainter::Antialiasing);    //  消除锯齿    

  5. *可以先画好图片放入pixmap中，再在窗口绘制

      QPixmap pixmap(size());
      QPainter p(&pixmap);
     
      QTransform transform;
      transform.translate(50,50);
      transform.rotate(30);
      p.setTransform(transform);
     
      p.drawxxx    ... ... 
      P.end();
     
      p.begin(this);
      p.drawPixmap(0,0,pixmap);

示例1（画板实现）

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// MyWidget.h 

#include<QVector>
#include <QDebug>
    class MyWidget : public QWidget
{
    Q_OBJECT
public:
    explicit MyWidget(QWidget *parent = nullptr);

    MyButton * button;


    void paintEvent(QPaintEvent *);
    void mousePressEvent(QMouseEvent *);
    void mouseReleaseEvent(QMouseEvent *);
    void mouseMoveEvent(QMouseEvent *);

    QVector<QPoint> _pos;

    QVector< QVector<QPoint> > _lines;

signals:

};

---

---

//MyWidget.cpp

void MyWidget::paintEvent(QPaintEvent *event)
{
    QPainter p(this);
    for(int i = 0; i < _lines.size();++i)
    {
        const QVector<QPoint> & line = _lines.at(i);
        {
            for(int j = 0; j < line.size()-1; ++j)
            {
                p.drawLine(line.at(j),line.at(j+1));
            }
        }
    }
}

void MyWidget::mouseMoveEvent(QMouseEvent *event)
{

    if(_lines.size() == 0)
    {
        QVector<QPoint> line;
        _lines.append(line);
    }

    QVector<QPoint>& lastline = _lines.last();
    lastline.append(event->pos());
//    _pos.append(event->pos());
    update();
}

void MyWidget::mouseReleaseEvent(QMouseEvent *event)
{
    QVector<QPoint>& lastline = _lines.last();
    lastline.append(event->pos());

//    _pos.append(event->pos());
}

void MyWidget::mousePressEvent(QMouseEvent *event)
{
    QVector<QPoint> line;   //  一条线
    _lines.append(line);     // 一条线放入很多条线 的向量里


    QVector<QPoint>& lastline = _lines.last();
    lastline.append(event->pos());

//    _pos.append(event->pos());
}

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示例2 按钮变色

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//  MyButton.h
#ifndef MYBUTTON_H
#define MYBUTTON_H

#include <QWidget>
#include <QMouseEvent>

class MyButton : public QWidget
{
    Q_OBJECT
public:
    explicit MyButton(QWidget *parent = nullptr);

    MyButton(const QString &text, QWidget* parent = 0);
    QRect _rect;    //  按钮大小
    QString _text;  //  按钮显示文字

    bool _pressed;  //  按压判断

    void paintEvent(QPaintEvent *event);

    void mousePressEvent(QMouseEvent *event);
    void mouseReleaseEvent(QMouseEvent *event);


signals:

    void clicked();

};

#endif // MYBUTTON_H

---

---

//  MuButton.cpp

#include "MyButton.h"
#include <QPainter>

MyButton::MyButton(QWidget *parent) :
    QWidget(parent), _rect(0,0,100,30)
{
    _pressed = false;   //  初始时 按压设置为否
    this->setGeometry(_rect);

}

MyButton::MyButton(const QString &text, QWidget *parent):
                        QWidget(parent), _text(text), _rect(0,0,100,30)
{
    _pressed = false;
    this->setGeometry(_rect);
}

void MyButton::paintEvent(QPaintEvent *event)
{
    QPainter p(this);
    if( _pressed == true )
    {
        p.setBrush(Qt::yellow); //  设置背景为黄色
    }
    else
        p.setBrush(Qt::darkGray);   //  设置背景为灰色
    p.drawRect(_rect);  //  画按钮框
    p.drawText(_rect, _text, QTextOption(Qt::AlignCenter)); //  画文字
}

void MyButton::mousePressEvent(QMouseEvent *event)
{
    //  按下时 按钮状态为 true 更新颜色
    _pressed = true;
    update();
}

void MyButton::mouseReleaseEvent(QMouseEvent *event)
{
    //  释放时 按钮状态为 false 更新颜色
    _pressed = false;
    update();

    //  在设定框框的容器范围内才发送信号
    if(_rect.contains(event->pos()))
    {
    emit clicked();
    }
//    emit clicked();
}

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