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_OBJECT

public:
	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）