双缓冲

1.双缓冲原理

单缓冲：在paintEvent中直接绘制到屏幕，绘制过程被用户看到
双缓冲：先在redrawBuffer绘制到缓冲区，然后一次性显示完整结果
代码结构
单缓冲：所有绘制逻辑在paintEvent中
双缓冲：绘制逻辑分离到redrawBuffer，paintEvent仅负责显示缓冲区
性能影响
单缓冲：每次更新需要重复计算和绘制
双缓冲：可以优化为只在必要时重绘缓冲区（如数据变化时）

减少的时间是重绘的那部分时间，单缓冲是逐个绘制，双缓冲是整体绘制。

测试案例

1.Qt 实现绘制 5000 个小球移动，单缓冲和双缓冲效果对比

2.代码

关键代码对比:
单缓冲绘制: paintEvent 中通过 painter 绘制每一个 circle，一次 paintEvent 绘制 5000 次
双缓冲绘制: paintEvent 中直接绘制提前赋好像素值的成员变量 buffer 中的像素

doublebufferwidget.h

#include <QWidget>
#include <QPainter>
#include <QTimer>
#include <QPixmap>
#include <QPointF>
#include <QVector>
#include <cmath>
#include <QTime>
#include <QDebug>


class DoubleBufferWidget : public QWidget {
    Q_OBJECT
public:
    DoubleBufferWidget(QWidget *parent = nullptr) : QWidget(parent) {
        // 初始化缓冲区
        setWindowTitle("DoubleBuffer");
        buffer = QPixmap(size());
        buffer.fill(Qt::white);

        // 初始化动画数据
        for (int i = 0; i < 5000; ++i) {
            circles.append({
                QPointF(rand() % width(), rand() % height()),
                5.f + rand() % 10,
                QColor(rand() % 256, rand() % 256, rand() % 256),
                QPointF((rand() % 100 - 50) / 100.0, (rand() % 100 - 50) / 100.0)
            });
        }

        // 设置定时器更新动画
        QTimer *timer = new QTimer(this);
        connect(timer, &QTimer::timeout, this, &DoubleBufferWidget::updateAnimation);
        timer->start(16);
    }

    void resizeEvent(QResizeEvent *event) override {
        buffer = QPixmap(size());
        buffer.fill(Qt::white);
        QWidget::resizeEvent(event);
    }

    void paintEvent(QPaintEvent *event) override {
        QTime doublePaint;

        doublePaint.start();

        Q_UNUSED(event);
        QPainter painter(this);
        painter.drawPixmap(0, 0, buffer);

        qInfo() << "void paintEvent(QPaintEvent *event) doublePaint cost times:" << doublePaint.elapsed() << "ms";
    }

private slots:
    void updateAnimation() {
        // 更新所有圆形位置
        for (auto &circle : circles) {
            circle.pos += circle.velocity;

            if (circle.pos.x() - circle.radius < 0 || circle.pos.x() + circle.radius > width())
                circle.velocity.setX(-circle.velocity.x());
            if (circle.pos.y() - circle.radius < 0 || circle.pos.y() + circle.radius > height())
                circle.velocity.setY(-circle.velocity.y());
        }

        // 重新绘制到缓冲区
        redrawBuffer();

        update();
    }

private:
    struct Circle {
        QPointF pos;
        qreal radius;
        QColor color;
        QPointF velocity;
    };

    QPixmap buffer;
    QVector<Circle> circles;

    void redrawBuffer() {
        buffer.fill(Qt::white);
        QPainter bufferPainter(&buffer);
        bufferPainter.setRenderHint(QPainter::Antialiasing);

        // 模拟长时间绘制过程
        for (int i = 0; i < 1000; ++i) {
            double temp = std::sin(i);
            Q_UNUSED(temp);
        }

        // 绘制所有圆形
        for (const auto &circle : circles) {
            bufferPainter.setPen(Qt::NoPen);
            bufferPainter.setBrush(circle.color);
            bufferPainter.drawEllipse(circle.pos, circle.radius, circle.radius);
        }
    }
};

singlebufferwidget.h

#include <QWidget>
#include <QTime>
#include <QPainter>
#include <QTimer>
#include <math.h>
#include <qmath.h>
#include <QDebug>

QT_BEGIN_NAMESPACE
namespace Ui { class SingleBufferWidget; }
QT_END_NAMESPACE

class SingleBufferWidget : public QWidget {
    Q_OBJECT
public:
    SingleBufferWidget(QWidget *parent = nullptr) : QWidget(parent) {
        // 初始化动画数据
        for (int i = 0; i < 5000; ++i) {
            circles.append({
                QPointF(rand() % width(), rand() % height()),
                5.f + rand() % 10,
                QColor(rand() % 256, rand() % 256, rand() % 256),
                QPointF((rand() % 100 - 50) / 100.0, (rand() % 100 - 50) / 100.0)
            });
        }

        // 设置定时器更新动画
        QTimer *timer = new QTimer(this);
        connect(timer, &QTimer::timeout, this, &SingleBufferWidget::updateAnimation);
        timer->start(16);
    }

    void paintEvent(QPaintEvent *event) override {

        QTime SingpaintTimer;
        SingpaintTimer.start();

        Q_UNUSED(event);
        QPainter painter(this);
        painter.setRenderHint(QPainter::Antialiasing);

        // 模拟长时间绘制过程
        for (int i = 0; i < 1000; ++i) {
            // 这个循环会延长绘制时间，加剧闪烁现象
            double temp = std::sin(i);
            Q_UNUSED(temp);
        }

        // 绘制所有圆形
        for (const auto &circle : circles) {
            painter.setPen(Qt::NoPen);
            painter.setBrush(circle.color);
            painter.drawEllipse(circle.pos, circle.radius, circle.radius);
        }

        qInfo() << "void paintEvent(QPaintEvent *event) SingpaintTimer cost times:" << SingpaintTimer.elapsed() << "ms";
    }

private slots:
    void updateAnimation() {
        // 更新所有圆形位置
        for (auto &circle : circles) {
            circle.pos += circle.velocity;

            if (circle.pos.x() - circle.radius < 0 || circle.pos.x() + circle.radius > width())
                circle.velocity.setX(-circle.velocity.x());
            if (circle.pos.y() - circle.radius < 0 || circle.pos.y() + circle.radius > height())
                circle.velocity.setY(-circle.velocity.y());
        }

        update();
    }

private:
    struct Circle {
        QPointF pos;
        qreal radius;
        QColor color;
        QPointF velocity;
    };

    QVector<Circle> circles;
};

3.工程文件资源