Qt 之 简单截图功能（二）实现可移动选中区域

一、简述

在 Qt 之 简单截图功能（一）实现鼠标选中区域截图 中我们简单介绍了截图，也实现了简单截图，但是截完图片后不可以继续移动选中区域，这一篇中将讲述在选取完截图区域后可再次用鼠标拖动移动选中区域。

效果图：

二、代码之路

—— 完整代码请见文章结尾下载链接。

capturescreen.cpp

#include "capturescreen.h"
#include <QApplication>
#include <QDesktopWidget>
#include <QMouseEvent>

CaptureScreen::CaptureScreen(QWidget *parent)
	: QWidget(parent)
	, m_currentCaptureState(initCapture)
{
	initWindow();
	loadBackgroundPixmap();
}

CaptureScreen::~CaptureScreen()
{

}

void CaptureScreen::initWindow()
{
	this->setMouseTracking(true);
	// 由于存在类似QQ这样界面始终显示在最顶层，设置属性 Qt::WindowStaysOnTopHint;
	this->setWindowFlags(Qt::FramelessWindowHint | Qt::WindowStaysOnTopHint);
	setWindowState(Qt::WindowActive | Qt::WindowFullScreen);
	this->setMouseTracking(true);
}

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_currentCaptureState == initCapture)
	{
		m_currentCaptureState = beginCaptureImage;
		m_beginPoint = event->pos();
	}
	else if (event->button() == Qt::LeftButton && isPressPointInSelectRect(event->pos()))
	{
		m_currentCaptureState = beginMoveCaptureArea;
		setCursor(Qt::SizeAllCursor);
		m_beginMovePoint = event->pos();
	}

	return QWidget::mousePressEvent(event);
}

void CaptureScreen::mouseMoveEvent(QMouseEvent* event)
{
	if (m_currentCaptureState == beginCaptureImage)
	{
		m_endPoint = event->pos();
		update();
	}
	else if (m_currentCaptureState == beginMoveCaptureArea)
	{
		m_endMovePoint = event->pos();
		update();
	}

	// 根据鼠标是否在选中区域内设置鼠标样式;
	if (isPressPointInSelectRect(event->pos()))
	{
		setCursor(Qt::SizeAllCursor);
	}
	else if (!isPressPointInSelectRect(event->pos()) && m_currentCaptureState != beginMoveCaptureArea)
	{
		setCursor(Qt::ArrowCursor);
	}
	
	return QWidget::mouseMoveEvent(event);
}

void CaptureScreen::mouseReleaseEvent(QMouseEvent *event)
{
	if (m_currentCaptureState == beginCaptureImage)
	{
		m_currentCaptureState = finishCaptureImage;
		m_endPoint = event->pos();
		update();
	}
	else if (m_currentCaptureState == beginMoveCaptureArea)
	{
		m_currentCaptureState = finishMoveCaptureArea;
		m_endMovePoint = event->pos();
		update();
	}
	return QWidget::mouseReleaseEvent(event);
}

// 当前鼠标坐标是否在选取的矩形区域内;
bool CaptureScreen::isPressPointInSelectRect(QPoint mousePressPoint)
{
	QRect selectRect = getRect(m_beginPoint, m_endPoint);
	if (selectRect.contains(mousePressPoint))
	{
		return true;
	}

	return false;
}

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;

	switch (m_currentCaptureState)
	{
	case initCapture:
		break;
	case beginCaptureImage:
	case finishCaptureImage:
	case beginMoveCaptureArea:
	case finishMoveCaptureArea:
		m_currentSelectRect = getSelectRect();
		drawCaptureImage();
	default:
		break;
	}

	m_painter.end();  //重绘结束;
}

// 根据当前截取状态获取当前选中的截图区域;
QRect CaptureScreen::getSelectRect()
{
	if (m_currentCaptureState == beginCaptureImage || m_currentCaptureState == finishCaptureImage)
	{
		return getRect(m_beginPoint, m_endPoint);
	}
	else if (m_currentCaptureState == beginMoveCaptureArea || m_currentCaptureState == finishMoveCaptureArea)
	{
		return getMoveRect();
	}

	return QRect(0, 0, 0, 0);
}

// 绘制当前选中的截图区域;
void CaptureScreen::drawCaptureImage()
{
	m_capturePixmap = m_loadPixmap.copy(m_currentSelectRect);
	m_painter.drawPixmap(m_currentSelectRect.topLeft(), m_capturePixmap);
	m_painter.drawRect(m_currentSelectRect);
}

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();
	}
}

// 根据beginPoint , endPoint 获取当前选中的矩形
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;
}

// 获取移动后,当前选中的矩形;
QRect CaptureScreen::getMoveRect()
{
	// 通过getMovePoint方法先检查当前是否移动超出屏幕;
	QPoint movePoint = getMovePoint();
	QPoint beginPoint = m_beginPoint + movePoint;
	QPoint endPoint = m_endPoint + movePoint;
	// 结束移动选区时更新当前m_beginPoint , m_endPoint,防止下一次操作时截取的图片有问题;
	if (m_currentCaptureState == finishMoveCaptureArea)
	{
		m_beginPoint = beginPoint;
		m_endPoint = endPoint;
		m_beginMovePoint = QPoint(0, 0);
		m_endMovePoint = QPoint(0, 0);
	}
	return getRect(beginPoint, endPoint);
}

QPoint CaptureScreen::getMovePoint()
{
	QPoint movePoint = m_endMovePoint - m_beginMovePoint;
	QRect currentRect = getRect(m_beginPoint, m_endPoint);
	// 检查当前是否移动超出屏幕;

	//移动选区是否超出屏幕左边界;
	if (currentRect.topLeft().x() + movePoint.x() < 0)
	{
		movePoint.setX(0 - currentRect.topLeft().x());
	}
	//移动选区是否超出屏幕上边界;
	if (currentRect.topLeft().y() + movePoint.y() < 0)
	{
		movePoint.setY(0 - currentRect.topLeft().y());
	}
	//移动选区是否超出屏幕右边界;
	if (currentRect.bottomRight().x() + movePoint.x() > m_screenwidth)
	{
		movePoint.setX(m_screenwidth - currentRect.bottomRight().x());
	}
	//移动选区是否超出屏幕下边界;
	if (currentRect.bottomRight().y() + movePoint.y() > m_screenheight)
	{
		movePoint.setY(m_screenheight - currentRect.bottomRight().y());
	}

	return movePoint;
}

---

尾

以上在 Qt 之 实现简单截图功能（一） 的基础之上完成了 在选取完截图区域后，能够拖动截图区域选择新的区域，下一篇中将完成可以用鼠标拖动截图区域的各个顶点改变截图区域大小的功能，详情见下图。

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代码下载

Qt 之 实现简单截图功能（二）