详解Qt中的双缓冲机制与实例应用

#ifndef PAINTAREA_H
#define PAINTAREA_H
 
#include <QWidget>
#include <QPen>
#include <QBrush>
#include <QMouseEvent>
#include <QPainter>
 
// 绘图区域
class PaintArea : public QWidget
{
    Q_OBJECT
public:
    enum Shape{Dot, Line, Rectangle, RoundRect, Ellipse, Polygon, Polyline, Points, Arc, Path, Text, Pixmap};
    explicit PaintArea(QWidget *parent = nullptr);
    void setShape(Shape shape); // 设置形状
    void setPen(QPen pen); // 设置画笔
    void setBrush(QBrush brush); // 设置画刷
    void clear(); // 清除绘图区域
 
protected:
    void mousePressEvent(QMouseEvent *event); // 鼠标点击事件
    void mouseMoveEvent(QMouseEvent *event); // 鼠标移动事件
    void paintEvent(QPaintEvent *event); // 绘图事件
 
private:
    Shape m_shape; // 形状
    QPen m_pen; // 画笔
    QBrush m_brush; // 画刷
 
    QPixmap *m_pix; // 画布
    QPoint m_posStart; // 鼠标移动绘图的开始坐标
    QPoint m_posEnd; // 鼠标移动绘图的结束坐标
};
 
#endif // PAINTAREA_H

#include "PaintArea.h"
 
PaintArea::PaintArea(QWidget *parent) :
    QWidget(parent)
{
    // 设置尺寸
    this->setMinimumSize(600, 300);
 
    // 用调色板设置背景色
    this->setPalette(QPalette(Qt::white));
    this->setAutoFillBackground(true);
 
    // 初始化画布
    m_pix = new QPixmap(size()); // 此QPixmap对象用来准备随时接收绘制的内容
    m_pix->fill(Qt::white); // 填充背景色为白色
}
 
// 鼠标点击事件
void PaintArea::mousePressEvent(QMouseEvent *event)
{
    m_posStart = event->pos();
}
 
// 鼠标移动事件
void PaintArea::mouseMoveEvent(QMouseEvent *event)
{
    QPainter *painter = new QPainter;
 
    // 鼠标移动绘图在画布pix上
    painter->begin(m_pix);
    painter->setPen(m_pen);
 
    if(m_shape == Dot)
        painter->drawLine(m_posStart, event->pos());
    else if(m_shape == Line)
        painter->drawLine(m_posStart, event->pos());
 
    painter->end();
 
    // 形状为Dot时，也就是自由绘图模式时，才时刻更新开始点击坐标
    if(m_shape == Dot)
        m_posStart = event->pos();
 
    this->update();
}
 
// 绘图事件
void PaintArea::paintEvent(QPaintEvent *)
{
    QPainter painter(this);
    painter.drawPixmap(QPoint(0,0),*m_pix);
}
 
// 设置形状
void PaintArea::setShape(Shape shape)
{
    m_shape = shape;
}
 
// 设置画笔
void PaintArea::setPen(QPen pen)
{
    m_pen = pen;
}
 
// 设置画刷
void PaintArea::setBrush(QBrush brush)
{
    m_brush = brush;
}
 
// 清除绘图区域
void PaintArea::clear()
{
    QPixmap *clearPix  =new QPixmap(size());
    clearPix->fill(Qt::white);
    m_pix = clearPix;
    this->update();
}

PaintArea::PaintArea(QWidget *parent) :
    QWidget(parent)
{
    // 设置尺寸
    this->setMinimumSize(600, 300);
 
    // 用调色板设置背景色
    this->setPalette(QPalette(Qt::white));
    this->setAutoFillBackground(true);
 
    // 初始化画布
    m_pix = new QPixmap(size()); // 此QPixmap对象用来准备随时接收绘制的内容
    m_pix->fill(Qt::white); // 填充背景色为白色
}
 
// 鼠标移动事件
void PaintArea::mouseMoveEvent(QMouseEvent *event)
{
    QPainter *painter = new QPainter;
 
    // 鼠标移动绘图在画布pix上
    painter->begin(m_pix);
    painter->setPen(m_pen);
 
    if(m_shape == Dot)
        painter->drawLine(m_posStart, event->pos());
    else if(m_shape == Line)
        painter->drawLine(m_posStart, event->pos());
 
    painter->end();
 
    // 形状为Dot时，也就是自由绘图模式时，才时刻更新开始点击坐标
    if(m_shape == Dot)
        m_posStart = event->pos();
 
    this->update();
}
 
// 绘图事件
void PaintArea::paintEvent(QPaintEvent *)
{
    QPainter painter(this);
    painter.drawPixmap(QPoint(0,0), *m_pix);
}