qt学习：截图+键盘事件

效果

• 生成一个透明无边框全屏的窗口，然后按ctrl+b键就可以选择区域进行截图保存

步骤

• 新建一个项目
• 新建一个ctrlb类继承QMainWindow
• 新建一个CaptureScreen类继承QWidget
• 在main中启动ctrlb类

代码

ctrlb类.cpp

#include "ctrlb.h"
#include "capturescreen.h"
#include <QKeyEvent>
#include <QPixmap>
#include <QFileDialog>
#include <QProcess>
#include <QDebug>
#include <QFile>
#include <QTextStream>ctrlb::ctrlb(QWidget *parent): QMainWindow(parent) {}// 按键事件
void ctrlb::keyPressEvent(QKeyEvent *event) {if (event->key() == Qt::Key_B && event->modifiers() == Qt::ControlModifier) {triggerScreenshot();}
}
// 截图操作
void ctrlb::triggerScreenshot() {// 定义截图对象CaptureScreen *capture = new CaptureScreen();// 调用 close() 函数或用户点击关闭按钮时，窗口对象会被自动销毁capture->setAttribute(Qt::WA_DeleteOnClose); // 当完成截图操作后，会发送信号触发保存图片connect(capture, &CaptureScreen::signalCompleteCature, this, &ctrlb::handleScreenshot);// 显示截图窗口capture->show(); 
}
// 保存图片，参数是屏幕的截图
void ctrlb::handleScreenshot(const QPixmap &screenshot) {// 判断参数是否为空if (!screenshot.isNull()) {QString savePath =  "check.jpg";if (!savePath.isEmpty()) {// 保存为用户指定的文件screenshot.save(savePath, "JPG"); }}}

ctrlb类.h

#ifndef CTRLB_H
#define CTRLB_H#include <QMainWindow>class ctrlb : public QMainWindow
{Q_OBJECT
public:explicit ctrlb(QWidget *parent = nullptr);protected:void keyPressEvent(QKeyEvent *event) override;private:void triggerScreenshot();private slots:// 保存图片槽函数void handleScreenshot(const QPixmap &screenshot); 
};#endif // CTRLB_H

CaptureScreen类.cpp

#include "capturescreen.h"
#include <QApplication>
#include <QMouseEvent>
#include <QPixmap>
#include <QScreen>CaptureScreen::CaptureScreen(QWidget *parent): QWidget(parent), m_isMousePress(false)
{// 初始化窗口initWindow();//loadBackgroundPixmap();
}CaptureScreen::~CaptureScreen()
{}void CaptureScreen::initWindow()
{// 启用鼠标跟踪，移动的时候也会触发事件this->setMouseTracking(true);// 设置窗口为无边框模式this->setWindowFlags(Qt::FramelessWindowHint);// 设置窗口全屏显示setWindowState(Qt::WindowActive | Qt::WindowFullScreen);
}
// 抓取当前桌面内容作为背景快照
void CaptureScreen::loadBackgroundPixmap()
{// 获取当前主屏幕的 QScreen 对象QScreen *screen = QGuiApplication::primaryScreen();if (screen) {// 获取现在的整个屏幕m_loadPixmap = screen->grabWindow(0);}// 获取屏幕宽高m_screenwidth = m_loadPixmap.width();m_screenheight = m_loadPixmap.height();
}// 处理鼠标左键按下，记录起点位置
void CaptureScreen::mousePressEvent(QMouseEvent *event)
{// 判断是不是左键if (event->button() == Qt::LeftButton){// 画图标志m_isMousePress = true;// 记录起始位置m_beginPoint = event->pos();}return QWidget::mousePressEvent(event);
}// 处理鼠标移动，记录终点位置
void CaptureScreen::mouseMoveEvent(QMouseEvent* event)
{// 判断是否画图if (m_isMousePress){// 记录移动位置m_endPoint = event->pos();// 画矩形update();}return QWidget::mouseMoveEvent(event);
}// 处理鼠标松开，记录终点位置
void CaptureScreen::mouseReleaseEvent(QMouseEvent *event)
{// 记录结束位置m_endPoint = event->pos();// 结束画矩形m_isMousePress = false;return QWidget::mouseReleaseEvent(event);
}// 绘制事件
void CaptureScreen::paintEvent(QPaintEvent *event)
{// 初始化 QPainter 对象 m_painterm_painter.begin(this);// 半透明的黑色阴影，用于覆盖整个屏幕QColor shadowColor = QColor(0, 0, 0, 100);// 设置画笔m_painter.setPen(QPen(Qt::blue, 1, Qt::SolidLine, Qt::FlatCap));// 将获取到的屏幕放到窗口上m_painter.drawPixmap(0, 0, m_loadPixmap);// 绘制一个半透明的黑色矩形m_painter.fillRect(m_loadPixmap.rect(), shadowColor);// 如果鼠标正在移动，会绘制选中的矩形区域if (m_isMousePress){// 计算选区矩形QRect selectedRect = getRect(m_beginPoint, m_endPoint);// 保存选区内容m_capturePixmap = m_loadPixmap.copy(selectedRect);// 将选区内容绘制到窗口m_painter.drawPixmap(selectedRect.topLeft(), m_capturePixmap);// 绘制选区边框m_painter.drawRect(selectedRect);}// 释放对象m_painter.end();  //重绘结束;
}// 键盘事件
void CaptureScreen::keyPressEvent(QKeyEvent *event)
{// Esc 键退出截图;if (event->key() == Qt::Key_Escape){close();}// Enter键完成截图;if (event->key() == Qt::Key_Return || event->key() == Qt::Key_Enter){// 保存截图为 JPG 格式QString savePath = "screenshot.jpg";if (!m_capturePixmap.isNull()) {// 保存为 JPG 格式m_capturePixmap.save(savePath, "JPG");}// 发送截图完成信号emit signalCompleteCature(m_capturePixmap);close();}
}// 计算一个矩形区域并返回
QRect CaptureScreen::getRect(const QPoint &beginPoint, const QPoint &endPoint)
{// 矩形的左上角坐标、宽度和高度int x, y, width, height;width = qAbs(beginPoint.x() - endPoint.x());height = qAbs(beginPoint.y() - endPoint.y());x = beginPoint.x() < endPoint.x() ? beginPoint.x() : endPoint.x();y = beginPoint.y() < endPoint.y() ? beginPoint.y() : endPoint.y();//  创建矩形对象QRect selectedRect = QRect(x, y, width, height);// 避免宽或高为零时拷贝截图有误，设置最小为1if (selectedRect.width() == 0){selectedRect.setWidth(1);}if (selectedRect.height() == 0){selectedRect.setHeight(1);}// 返回矩形对象return selectedRect;
}

CaptureScreen类.h

#ifndef CAPTURESCREEN_H
#define CAPTURESCREEN_H#include <QWidget>
#include <QPainter>class CaptureScreen : public QWidget
{Q_OBJECTpublic:CaptureScreen(QWidget *parent = 0);~CaptureScreen();Q_SIGNALS:void signalCompleteCature(QPixmap catureImage);private:void initWindow();void loadBackgroundPixmap();void mousePressEvent(QMouseEvent *event);void mouseMoveEvent(QMouseEvent* event);void mouseReleaseEvent(QMouseEvent *event);void keyPressEvent(QKeyEvent *event);void paintEvent(QPaintEvent *event);QRect getRect(const QPoint &beginPoint, const QPoint &endPoint);private:bool m_isMousePress;// 判断鼠标是否移动和是否画矩形QPixmap m_loadPixmap;// 整个屏幕的图像QPixmap m_capturePixmap;// 框选的屏幕图像int m_screenwidth;// 屏幕的宽int m_screenheight;// 屏幕的高QPoint m_beginPoint, m_endPoint;// 起点和结束点坐标QPainter m_painter;// 画图对象
};#endif // CAPTURESCREEN_H

main

#include "mainwindow.h"#include <QApplication>
#include "ctrlb.h"
#include <QDebug>
#include <QWidget>int main(int argc, char *argv[])
{QApplication a(argc, argv);qDebug()<<"init";ctrlb w;// 设置无边框窗口w.setWindowFlags(Qt::FramelessWindowHint); // 全屏w.showFullScreen();// 背景透明w.setAttribute(Qt::WA_TranslucentBackground);// 设置透明度w.setWindowOpacity(1); w.show();return a.exec();
}