截图程序，支持多屏幕时跨屏幕截图。截图使用setMask达到镂空效果，截图后会有预览和保存功能。截图时按下Esc可退出。

mainwindow.ui

mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QDebug>
#include <QFileDialog>
#include <QPushButton>
#include <QPixmap>MainWindow::MainWindow(QWidget *parent): QMainWindow(parent), ui(new Ui::MainWindow)
{ui->setupUi(this);this->setWindowTitle(QString(tr("截图")));ui->centralwidget->setMouseTracking(true);ui->comboBox->addItem(QString(tr(".")));ui->comboBox->addItem(QString(tr("Select Folder")));connect(ui->comboBox, SIGNAL(activated(int)), this, SLOT(SelectFolder(int)));connect(ui->button_reset, SIGNAL(clicked(bool)), this, SLOT(ResetSnap(bool)));connect(ui->button_save, SIGNAL(clicked(bool)), this, SLOT(SavePicture(bool)));
}MainWindow::~MainWindow()
{delete ui;
}void MainWindow::mouseMoveEvent(QMouseEvent *event)
{qDebug()<<this->geometry();QMainWindow::mouseMoveEvent(event);
}void MainWindow::SetImage(QPixmap &pixmap)
{const double defultWidth = 400.0;const double defaultHeight = 160.0;ui->label->setPixmap(pixmap);double pixscale = 1.0 * pixmap.width()/pixmap.height();double initscale = defultWidth/defaultHeight;if (pixscale > initscale){ui->label->setFixedWidth(defultWidth);ui->label->setFixedHeight(defultWidth / pixscale);}else{ui->label->setFixedHeight(defaultHeight);ui->label->setFixedWidth(defaultHeight * pixscale);}
}void MainWindow::SelectFolder(int index)
{if (index == 1){qDebug()<<ui->comboBox->itemText(index);QString directory = QFileDialog::getExistingDirectory(this,tr("QFileDialog::getExistingDirectory()"),".");if (!directory.isEmpty()){qDebug()<<directory;ui->comboBox->addItem(directory);ui->comboBox->setCurrentText(directory);}else{ui->comboBox->setCurrentIndex(0);}}
}void MainWindow::ResetSnap(bool)
{this->hide();emit resetSnap();
}void MainWindow::SavePicture(bool)
{if (ui->lineEdit->text().trimmed() == QString("")){ui->lineEdit->setFocus();return;}if (ui->comboBox->currentText() != "."){ui->label->pixmap()->save(ui->comboBox->currentText() + "/" + ui->lineEdit->text(), "PNG");}else{ui->label->pixmap()->save(ui->lineEdit->text(), "PNG");}
}

maskwidget.cpp

#include "maskwidget.h"
#include "ui_maskwidget.h"
#include <QMouseEvent>
#include <QRegion>
#include <QScreen>
#include <QPainter>
#include <QGuiApplication>
#include <QPixmap>
#include <QDebug>
#include <QtMath>MaskWidget::MaskWidget(QWidget *parent) :QWidget(parent),ui(new Ui::MaskWidget)
{ui->setupUi(this);setMouseTracking(true);setWindowFlags(Qt::FramelessWindowHint);setWindowOpacity(0.8);QList<QScreen*> screens = QGuiApplication::screens();int width = 0;int height = 0;for (QScreen *screen : screens){width += screen->geometry().width();if (height < screen->geometry().height()){height = screen->geometry().height();}qDebug()<<screen->geometry();}this->setFixedSize(width, height);m.hide();connect(&m, SIGNAL(resetSnap()), this, SLOT(ResetSnap()));
}MaskWidget::~MaskWidget()
{delete ui;
}void MaskWidget::mousePressEvent(QMouseEvent *event)
{if (event->button() == Qt::LeftButton){m_pressPos = event->pos();isPressed = true;update();}QWidget::mousePressEvent(event);
}void MaskWidget::mouseReleaseEvent(QMouseEvent *event)
{if (isPressed){isPressed = false;QRegion all(0, 0, width(), height());QRegion sub(m_maskRect);setMask(all.subtracted(sub));QPixmap combined(this->width(), this->height());combined.fill(Qt::transparent);QPainter painter(&combined);QList<QScreen*> screens = QGuiApplication::screens();for (QScreen *screen : screens){m_image = screen->grabWindow(0);painter.drawPixmap(screen->geometry().x(), 0, screen->geometry().width(), screen->geometry().height(), m_image);}auto gpos = mapToGlobal(event->pos());auto gposStart = mapToGlobal(m_pressPos);qDebug()<<gpos<<gposStart;m_image = combined.copy(qMin(gpos.x(), gposStart.x()), qMin(gpos.y(), gposStart.y()),qFabs(gpos.x() - gposStart.x()), qFabs(gpos.y() - gposStart.y()));this->hide();m.SetImage(m_image);update();m.show();}return QWidget::mouseReleaseEvent(event);
}void MaskWidget::mouseMoveEvent(QMouseEvent* event)
{if (isPressed){m_newPos = event->pos();QRegion all(0, 0, width(), height());m_maskRect = QRect(qMin(m_pressPos.x(), m_newPos.x()),qMin(m_pressPos.y(), m_newPos.y()),qFabs(m_newPos.x() - m_pressPos.x()),qFabs(m_newPos.y() - m_pressPos.y()));QRegion sub(m_maskRect);setMask(all.subtracted(sub));update();}return QWidget::mouseMoveEvent(event);
}void MaskWidget::paintEvent(QPaintEvent *event)
{QPainter painter(this);painter.setPen(Qt::red);painter.drawRect(m_maskRect.x()-1, m_maskRect.y()-1, m_maskRect.width()+2, m_maskRect.height() + 2);}void MaskWidget::keyPressEvent(QKeyEvent *event)
{if (event->key() == Qt::Key_Escape){close();}QWidget::keyPressEvent(event);
}void MaskWidget::showEvent(QShowEvent *event)
{QWidget::showEvent(event);
}void MaskWidget::ResetSnap()
{QRegion all(0, 0, width(), height());setMask(all);m_maskRect.setRect(0,0,0,0);this->show();
}

main.cpp

#include "mainwindow.h"
#include "maskwidget.h"
#include <QApplication>int main(int argc, char *argv[])
{QApplication a(argc, argv);MaskWidget m;m.move(0, 0);m.show();return a.exec();
}

多个屏幕时，默认设置位置和大小总是在一个屏，需要用move()将它移动到(0, 0)位置。多屏幕跨屏幕截图时，先分别截取每个屏幕的图，然后把他们拼起来。

代码