Qt简单截屏

#ifndef GRABWIDGET_H
#define GRABWIDGET_H

#include <QWidget>
#include <QMouseEvent>

class GrabWidget : public QWidget
{
    Q_OBJECT
public:
    explicit GrabWidget(QWidget *parent = 0);

signals:

public slots:

public:
    void savePixmap();

protected:
    void mouseMoveEvent(QMouseEvent *ev);
    void paintEvent(QPaintEvent *);
    void mousePressEvent(QMouseEvent *ev);
    void mouseReleaseEvent(QMouseEvent *ev);

private:
    QPoint ptCur_;
    QPoint ptStart_;
    QPoint ptEnd_;
    bool isDrawing_;
};

#endif // GRABWIDGET_H

#include "grabwidget.h"
#include <QApplication>
#include <QtGui>
#include <QDesktopWidget>

GrabWidget::GrabWidget(QWidget *parent) :
    QWidget(parent)
{
    setWindowFlags(Qt::Widget | Qt::FramelessWindowHint);
    setWindowOpacity(0.1);
    resize(QApplication::desktop()->width(), QApplication::desktop()->height());
    setCursor(Qt::CrossCursor);
    isDrawing_ = false;
}

void GrabWidget::savePixmap()
{

}

void GrabWidget::mouseMoveEvent(QMouseEvent *ev)
{
    ptCur_.setX(ev->x());
    ptCur_.setY(ev->y());
    update();
}

void GrabWidget::paintEvent(QPaintEvent *e)
{
    QWidget::paintEvent(e);

    int width, height;
    QPainter painter(this);
    painter.setPen(Qt::red);
    if (isDrawing_) {
        width = ptCur_.x() - ptStart_.x();
        height = ptCur_.y() - ptStart_.y();
        painter.drawRect(ptStart_.x(), ptStart_.y(), width, height);
    } else {
        if (ptEnd_ != ptStart_) {
            width = ptEnd_.x() - ptStart_.x();
            height = ptEnd_.y() - ptStart_.y();
            painter.drawRect(ptStart_.x(), ptStart_.y(), width, height);
        }
    }
}

void GrabWidget::mousePressEvent(QMouseEvent *ev)
{
    if (ev->button() == Qt::MiddleButton) {
        hide();
        int width = ptEnd_.x() - ptStart_.x();
        int height = ptEnd_.y() - ptStart_.y();
        QPixmap tmpPixmap = QPixmap::grabWindow(QApplication::desktop()->winId(),
                                                ptStart_.x(), ptStart_.y(), width, height);
        QDateTime dt = QDateTime::currentDateTime();
        QString filename = dt.toString("yyyyMMddhhmmss") + ".jpg";
        tmpPixmap.save(filename, 0, 100);
        exit(1);
    } else if (ev->button() == Qt::RightButton) {
        exit(1);
    } else if (ev->button() == Qt::LeftButton) {
        ptStart_ = ev->pos();
        isDrawing_ = true;
    }
    update();
}

void GrabWidget::mouseReleaseEvent(QMouseEvent *ev)
{
    if (ev->button() == Qt::LeftButton) {
        ptEnd_ = ev->pos();
        isDrawing_ = false;
    }
}

#include <QApplication>
#include "grabwidget.h"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    GrabWidget grabWidget;
    grabWidget.setMouseTracking(true);
    grabWidget.show();

    return a.exec();
}