网站建设的费用市场推广策略 包括哪些
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
双缓冲和单缓冲效果对比
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_NAMESPACEclass 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;
};