一、简述
之前用Qt实现了类似于QQ的截图功能，由于代码太多，一下子不一定明白，今天就用一个简单的小例子来看一看如何用Qt实现一个简单的截图功能。此篇文章中代码很简单，功能也比较简单，在后续的文章中将会逐步完善。先看来一下简单的效果图。
效果图
正向截取
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反向截取
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上图是通过点击截图按钮，然后选择区域，按下Enter键进行截图并显示到主窗口中。
其实实现截图的原理很简单，就是事先截取整个屏幕，然后根据鼠标选择区域进行截取，主要难点在于获取选中的区域，此篇中获取选中区域代码较为简单，存在一定的问题，后续会详细讲解，并加以完善。
下面是目前已经实现的效果。
已完成效果
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二、代码之路
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);private:bool m_isMousePress;QPixmap m_loadPixmap, m_capturePixmap;int m_screenwidth;int m_screenheight;QPoint m_beginPoint, m_endPoint;QPainter m_painter;
};
capturescreen.cpp
#include "capturescreen.h"
#include <QApplication>
#include <QDesktopWidget>
#include <QMouseEvent>CaptureScreen::CaptureScreen(QWidget *parent): QWidget(parent), m_isMousePress(false)
{initWindow();loadBackgroundPixmap();
}CaptureScreen::~CaptureScreen()
{}void CaptureScreen::initWindow()
{this->setMouseTracking(true);this->setWindowFlags(Qt::FramelessWindowHint);setWindowState(Qt::WindowActive | Qt::WindowFullScreen);
}void CaptureScreen::loadBackgroundPixmap()
{m_loadPixmap = QPixmap::grabWindow(QApplication::desktop()->winId()); //抓取当前屏幕的图片;m_screenwidth = m_loadPixmap.width();m_screenheight = m_loadPixmap.height();
}void CaptureScreen::mousePressEvent(QMouseEvent *event)
{if (event->button() == Qt::LeftButton){m_isMousePress = true;m_beginPoint = event->pos();}return QWidget::mousePressEvent(event);
}void CaptureScreen::mouseMoveEvent(QMouseEvent* event)
{if (m_isMousePress){m_endPoint = event->pos();update();}return QWidget::mouseMoveEvent(event);
}void CaptureScreen::mouseReleaseEvent(QMouseEvent *event)
{m_endPoint = event->pos();m_isMousePress = false;return QWidget::mouseReleaseEvent(event);
}void CaptureScreen::paintEvent(QPaintEvent *event)
{m_painter.begin(this); //进行重绘;QColor shadowColor = QColor(0, 0, 0, 100); //阴影颜色设置;m_painter.setPen(QPen(Qt::blue, 1, Qt::SolidLine, Qt::FlatCap)); //设置画笔;m_painter.drawPixmap(0, 0, m_loadPixmap); //将背景图片画到窗体上;m_painter.fillRect(m_loadPixmap.rect(), shadowColor); //画影罩效果;if (m_isMousePress){QRect selectedRect = getRect(m_beginPoint, m_endPoint);m_capturePixmap = m_loadPixmap.copy(selectedRect);m_painter.drawPixmap(selectedRect.topLeft(), m_capturePixmap);m_painter.drawRect(selectedRect);}m_painter.end(); //重绘结束;
}void CaptureScreen::keyPressEvent(QKeyEvent *event)
{// Esc 键退出截图;if (event->key() == Qt::Key_Escape){close();}// Eeter键完成截图;if (event->key() == Qt::Key_Return || event->key() == Qt::Key_Enter){signalCompleteCature(m_capturePixmap);close();}
}QRect CaptureScreen::getRect(const QPoint &beginPoint, const QPoint &endPoint)
{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();QRect selectedRect = QRect(x, y, width, height);// 避免宽或高为零时拷贝截图有误;// 可以看QQ截图，当选取截图宽或高为零时默认为2;if (selectedRect.width() == 0){selectedRect.setWidth(1);}if (selectedRect.height() == 0){selectedRect.setHeight(1);}return selectedRect;
}
测试代码
void TestWindow::onCatureImage()
{// 点击截图按钮开始截图;CaptureScreen* captureHelper = new CaptureScreen();connect(captureHelper, SIGNAL(signalCompleteCature(QPixmap)), this, SLOT(onCompleteCature(QPixmap)));captureHelper->show();
}void TestWindow::onCompleteCature(QPixmap captureImage)
{ui.label->setPixmap(captureImage);
}
尾
以上代码实现了一个简单的截图功能，后续会完善并增加更多的功能，争取能够实现QQ截图的效果 ，敬请期待 O(∩_∩)O！
Good Night ！！！
代码下载
Qt 之 实现简单截图功能（一）
