QT实现截屏功能

    最近因为需要开发一个类似QQ的截屏功能，花了不少的时间，开始的时候很多也不懂，不知道如何下手，在网上找了很多的资料，现已经实现了截屏，移动截屏选区，通过拖动选区的八个控制点来改变选区的大小。

    QT实现截屏的原理是，当点击截屏按钮（菜单栏上的截屏按钮）时，调用fullScreenWidget对象getFullScreenPixmap()方法，返回当前屏幕的QPixmap图片对象。在构造调用窗体的构造函数中，关联信号与槽，使其在点击“截屏”按钮发送信息给fullScreenWidget对象对应的槽函数，以便加载当前的背景图片。

connect(newAct,SIGNAL(triggered()),this,SLOT(screenshot()));

connect(this,SIGNAL(setPixmap(QPixmap)),fullWidget,SLOT(loadBackgroundPixmap(QPixmap)));

    在fullScreenWidget类中，主要是根据当前截屏的状态来实时的判断如果截取屏幕。我在类中定义了shotState枚举类型，用来判断当前截屏的状态。定义了QPoint beginPoint,endPoint,moveBeginPoint,moveEndPoint;四个对象主要用来记录开始，结束的截屏坐标。移动的开始，结束坐标。根据不同的截屏状态和这4个坐标点的值来计算截屏的区域。我的表达能力不太好，先把核心代码上面来。fullScreenWidget.h头文件代码如下：

#ifndef FULLSCREENWIDGET_H
#define FULLSCREENWIDGET_H

#include <QWidget>
#include <QPixmap>
#include <QPoint>
#include <QtGui>
#include <QPainter>
#include <QBrush>

class fullScreenWidget : public QWidget{

  Q_OBJECT

  public:
  fullScreenWidget(); //构造函数
  enum shotState{initShot,beginShot,finishShot,endShot,beginMoveShot,finishMoveShot,beginControl,finishControl}; //进行截屏的状态
  //移动选区中的8个控制点，按照顺时针方向从左上控制点到左中控制点分配编号为1～8
  enum controlPointEnum{moveControl0,moveControl1,moveControl2,moveControl3,moveControl4,moveControl5,moveControl6,moveControl7,moveControl8};
  QPixmap getFullScreenPixmap(); //获取全屏的Pixmap

  public slots:
  void loadBackgroundPixmap(const QPixmap &bgPixmap);//加载背景Pixmap槽函数
  void loadBackgroundPixmap(const QPixmap &bgPixmap, int x, int y, int width, int height); //加载背景pixmap槽函数，设置x,y,width,height
  void cancelSelectedRect(); //取消选择区域
  void savePixmap(); //保选取行为的方法

  signals:
  void finishPixmap(const QPixmap &finishPixmap); //完成切图后的图片,发送信号给连接者

  private:
  //选区框的8个点选取
  QRect tlRect; //左上点
  QRect trRect; //右上点
  QRect blRect; //左下点
  QRect brRect; //右下点
  QRect tcRect; //上中点
  QRect bcRect; //下中点
  QRect lcRect;//左中点
  QRect rcRect; //右中点

  QPainter painter;
  QPoint beginPoint,endPoint,moveBeginPoint,moveEndPoint;
  QRect selectedRect; //选择区域
  QPixmap loadPixmap,shotPixmap;
  shotState currentShotState; //当前的截屏状态
  controlPointEnum controlValue; //记录移动控制点的值
  QAction *savePixmapAction; //保存图片行为
  QAction *cancelAction; //取消选取行为
  QAction *quitAction; //退出选取行为
  QMenu *contextMenu; //选中区域右键菜单
  int screenwidth; //整个屏幕的宽度
  int screenheight; //整个屏幕的高度
  int screenx; //选区的X
  int screeny; //选区的Y
  int tipWidth,tipHeight,infoWidth,infoHeight; //加载初始框的宽度，高度；显示坐标信息的宽度，高度

  QRect getSelectedRect(); //获取选取
  QRect getRect(const QPoint &beginPoint, const QPoint &endPoint); //根据两个点获取选取坐标
  void initFullScreenWidget(); //初始化抓全屏的相关参数
  bool isInSelectedRect(const QPoint &point); //判断该点是否在选中区域
  void initSelectedMenu();//初始化右键菜单
  void drawTipsText(); //在屏幕上打印提示信息
  void drawSelectedPixmap(void); //在屏幕上画选取的屏幕
  void updateBeginEndPointValue(const QRect &rect);  //当移动选取后，对beginPoint,endPoint坐标进行重新修改
  void checkMoveEndPoint(); //对移动的选区进行判断
  void draw8ControlPoint(const QRect &rect);
  void updateMouseShape(const QPoint &point); //更新鼠标的当前状态
  void updateMoveControlMouseShape(controlPointEnum controlValue);
  controlPointEnum getMoveControlState(const QPoint &point); //获取移动控制点状态
  QRect getMoveAllSelectedRect(void); //获取移动整个选中的选区
  QRect getMoveControlSelectedRect(void);//获取移动控制点的选区
  int getMinValue(int num1, int num2);//获取两个数中的最小值
  void drawXYWHInfo(void); //打印选取的x,y,h,w值信息

  //重写基类方法
  void keyPressEvent(QKeyEvent *event);
  void paintEvent(QPaintEvent *event);
  void mousePressEvent(QMouseEvent *event);
  void mouseReleaseEvent(QMouseEvent *event);
  void mouseMoveEvent(QMouseEvent *event);
  void mouseDoubleClickEvent(QMouseEvent *event);
  void contextMenuEvent(QContextMenuEvent *event);
};

#endif

fullScreenWidget.cpp类的实现文件如下：

#include "fullScreenWidget.h"
fullScreenWidget::fullScreenWidget()
{
  setWindowState(Qt::WindowActive|Qt::WindowFullScreen);
  tipWidth = 300; //温馨提示框的宽度
  tipHeight = 100; //温馨提示框的高度
  infoWidth = 100; //坐标信息框的宽度
  infoHeight = 50; //坐标信息框的高度
  initFullScreenWidget();
}

void fullScreenWidget::initSelectedMenu()
{
  savePixmapAction = new QAction(tr("保存选区"),this);
  cancelAction = new QAction(tr("重选"),this);
  quitAction = new QAction(tr("退出"),this);
  contextMenu = new QMenu(this);

  connect(savePixmapAction,SIGNAL(triggered()),this,SLOT(savePixmap()));
  connect(cancelAction,SIGNAL(triggered()),this,SLOT(cancelSelectedRect()));
  connect(quitAction,SIGNAL(triggered()),this,SLOT(hide()));
}

void fullScreenWidget::savePixmap()
{
  QString fileName;
  fileName = QFileDialog::getSaveFileName(this,tr("保存图片"),QDir::currentPath(),tr("Images (*.jpg *.png *.bmp)"));
  if(fileName.isNull())
    return;

  shotPixmap.save(fileName);
  hide();
}

void fullScreenWidget::loadBackgroundPixmap(const QPixmap &bgPixmap)
{
  int width,height;
  width = QApplication::desktop()->size().width();
  height = QApplication::desktop()->size().height();

  loadBackgroundPixmap(bgPixmap,0,0,width,height);
}

void fullScreenWidget::loadBackgroundPixmap(const QPixmap &bgPixmap, int x, int y, int width, int height)
{
  loadPixmap = bgPixmap;
  screenx = x;
  screeny = y;
  screenwidth = width;
  screenheight = height;
  initFullScreenWidget();
}

QPixmap fullScreenWidget::getFullScreenPixmap()
{
  initFullScreenWidget();
  QPixmap result = QPixmap();
  result = QPixmap::grabWindow(QApplication::desktop()->winId()); //抓取当前屏幕的图片

  return result;
}

void fullScreenWidget::paintEvent(QPaintEvent *event)
{
  QColor shadowColor;
  shadowColor= QColor(0,0,0,100); //阴影颜色设置
  painter.begin(this); //进行重绘

  painter.setPen(QPen(Qt::blue,2,Qt::SolidLine,Qt::FlatCap));//设置画笔
  painter.drawPixmap(screenx,screeny,loadPixmap); //将背景图片画到窗体上
  painter.fillRect(screenx,screeny,screenwidth,screenheight,shadowColor); //画影罩效果

  switch(currentShotState){
    case initShot:
      drawTipsText();
      break;
    case beginShot:
    case finishShot:
      selectedRect = getRect(beginPoint,endPoint); //获取选区
      drawSelectedPixmap();
      break;
    case beginMoveShot:
    case finishMoveShot:
      selectedRect = getMoveAllSelectedRect(); //获取选区
      drawSelectedPixmap();
      break;
    case beginControl:
    case finishControl:
      selectedRect = getMoveControlSelectedRect();
      drawSelectedPixmap();
      break;
    default:
      break;
  }
  drawXYWHInfo(); //打印坐标信息
  painter.end();  //重绘结束

  if(currentShotState == finishMoveShot || currentShotState == finishControl){
    updateBeginEndPointValue(selectedRect); //当移动完选区后，更新beginPoint,endPoint;为下一次移动做准备工作
  }

}

void fullScreenWidget::keyPressEvent(QKeyEvent *event)
{
  if(event->key() == Qt::Key_Escape){
    initFullScreenWidget();
    hide();
  }
}

void fullScreenWidget::mousePressEvent(QMouseEvent *event)
{
  //当开始进行拖动进行选择区域时,确定开始选取的beginPoint坐标
  if(event->button() == Qt::LeftButton && currentShotState == initShot){
    currentShotState = beginShot; //设置当前状态为beginShot状态
    beginPoint = event->pos();
  }

  //移动选区改变选区的所在位置
  if(event->button() == Qt::LeftButton && isInSelectedRect(event->pos()) &&
     getMoveControlState(event->pos()) == moveControl0){
      currentShotState = beginMoveShot; //启用开始移动选取选项,beginMoveShot状态
      moveBeginPoint = event->pos();
  }
  //移动控制点改变选区大小
  if(event->button() == Qt::LeftButton && getMoveControlState(event->pos()) != moveControl0){
    currentShotState = beginControl; //开始移动控制点
    controlValue = getMoveControlState(event->pos());
    moveBeginPoint = event->pos();
  }
}

void fullScreenWidget::mouseReleaseEvent(QMouseEvent *event)
{
  if(event->button() == Qt::LeftButton && currentShotState == beginShot){
    currentShotState = finishShot;
    endPoint = event->pos();
    update();
  }

  if(event->button() == Qt::LeftButton && currentShotState == beginMoveShot){
    currentShotState = finishMoveShot;
    moveEndPoint = event->pos();
    update();
  }

  //当前状态为beginControl状态时，设置状态为finishControl
  if(event->button() == Qt::LeftButton && currentShotState == beginControl){
    currentShotState = finishControl;
    moveEndPoint = event->pos();
    update();
  }
}

void fullScreenWidget::mouseMoveEvent(QMouseEvent *event)
{
  //当拖动时，动态的更新所选择的区域
  if(currentShotState == beginShot){
    endPoint = event->pos();
    update();
  }

  //当确定选区后，对选区进行移动操作
  if(currentShotState == beginMoveShot || currentShotState == beginControl){
    moveEndPoint = event->pos();
    update();
  }

  updateMouseShape(event->pos()); //修改鼠标的形状
  setMouseTracking(true);
}

void fullScreenWidget::mouseDoubleClickEvent(QMouseEvent *event)
{
  if(currentShotState == finishShot || currentShotState == finishMoveShot || currentShotState == finishControl){
    emit finishPixmap(shotPixmap); //当完成时发送finishPixmap信号
    hide();
  }
}

QRect fullScreenWidget::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();

  return QRect(x,y,width,height);
}

void fullScreenWidget::initFullScreenWidget()
{
    currentShotState = initShot;
    controlValue = moveControl0;
    beginPoint =QPoint(0,0);
    endPoint = QPoint(0,0);
    moveBeginPoint = QPoint(0,0);
    moveEndPoint = QPoint(0,0);

    tlRect = QRect(0,0,0,0); //左上点
    trRect = QRect(0,0,0,0); //上右点
    blRect = QRect(0,0,0,0); //左下点
    brRect = QRect(0,0,0,0); //右下点
    tcRect = QRect(0,0,0,0); //上中点
    bcRect = QRect(0,0,0,0); //下中点
    lcRect = QRect(0,0,0,0); //左中点
    rcRect = QRect(0,0,0,0); //右中点

    setCursor(Qt::CrossCursor);
}

bool fullScreenWidget::isInSelectedRect(const QPoint &point)
{
  int x,y;
  QRect selectedRect;
  if(currentShotState == initShot || currentShotState == beginShot)
    return false;

  selectedRect = getSelectedRect();
  x = point.x();
  y = point.y();

  return selectedRect.contains(x,y);
}

void fullScreenWidget::cancelSelectedRect()
{
  initFullScreenWidget();
  update(); //进行重绘，将选取区域去掉
}

void fullScreenWidget::contextMenuEvent(QContextMenuEvent *event)
{
  initSelectedMenu();

  if(isInSelectedRect(event->pos())){
    contextMenu->addAction(savePixmapAction);
  }
  else{
    contextMenu->addAction(cancelAction);
    contextMenu->addAction(quitAction);
  }

  contextMenu->exec(event->pos());
}

void fullScreenWidget::drawTipsText()
{
  int x = (screenwidth - tipWidth)/2;
  int y = (screenheight - tipHeight)/2;
  QColor color = QColor(100,100,100,200);
  QRect rect = QRect(x,y,tipWidth,tipHeight);
  QString strTipsText = QString(tr("温馨提示\n鼠标拖动进行截屏;截屏区域内右键保存;\n截屏区域外右键取消;ESC退出;"));

  painter.fillRect(rect,color);
  painter.setPen(QPen(Qt::white));//设置画笔的颜色为白色
  painter.drawText(rect,Qt::AlignCenter,strTipsText);

}

QRect fullScreenWidget::getSelectedRect()
{
  if(currentShotState == beginMoveShot){
     return getMoveAllSelectedRect();
  }
  else if(currentShotState == beginControl){
     return getMoveControlSelectedRect();
  }
  else{
    return getRect(beginPoint,endPoint);
  }
}

void fullScreenWidget::updateBeginEndPointValue(const QRect &rect)
{
  beginPoint = rect.topLeft();
  endPoint = rect.bottomRight();

  moveBeginPoint = QPoint(0,0);
  moveEndPoint = QPoint(0,0);
}

void fullScreenWidget::checkMoveEndPoint()
{
  int x,y;
  QRect selectedRect = getRect(beginPoint, endPoint);
  QPoint bottomRightPoint = selectedRect.bottomRight();
  x = moveEndPoint.x() - moveBeginPoint.x();
  y = moveEndPoint.y() - moveBeginPoint.y();

  if(x + selectedRect.x() < 0){ //当移动后X坐标小于零时，则出现选区丢失，则计算出moveEndPoint的X最大坐标值，进行赋值
    moveEndPoint.setX(qAbs(selectedRect.x()-moveBeginPoint.x()));
  }

  if(y + selectedRect.y() < 0){ //当移动后Y坐标小于零时，则出现选区丢失，则计算出moveEndPoint的Y最大坐标值，进行赋值
    moveEndPoint.setY(qAbs(selectedRect.y() - moveBeginPoint.y()));
  }

  if(x + bottomRightPoint.x() > screenwidth){ //当移动选区后，出现超出整个屏幕的右面时，设置moveEndPoint的X的最大坐标
    moveEndPoint.setX(screenwidth - bottomRightPoint.x() + moveBeginPoint.x());
  }

  if(y + bottomRightPoint.y() > screenheight){ //当移动选区后，出现超出整个屏幕的下面时，设置moveEndPoint的Y的最大坐标值
    moveEndPoint.setY(screenheight - bottomRightPoint.y() + moveBeginPoint.y());
  }
}

void fullScreenWidget::draw8ControlPoint(const QRect &rect)
{
  int x,y;
  QColor color= QColor(0,0,255); //画点的颜色设置
  QPoint tlPoint = rect.topLeft(); //左上点
  QPoint trPoint = rect.topRight(); //右上点
  QPoint blPoint = rect.bottomLeft(); //左下点
  QPoint brPoint = rect.bottomRight(); //右下点

  x = (tlPoint.x()+trPoint.x())/2;
  y = tlPoint.y();
  QPoint tcPoint = QPoint(x,y);

  x = (blPoint.x()+brPoint.x())/2;
  y = blPoint.y();
  QPoint bcPoint = QPoint(x,y);

  x = tlPoint.x();
  y = (tlPoint.y()+blPoint.y())/2;
  QPoint lcPoint = QPoint(x,y);

  x = trPoint.x();
  y = (trPoint.y()+brPoint.y())/2;
  QPoint rcPoint = QPoint(x,y);

  tlRect = QRect(tlPoint.x()-2,tlPoint.y()-2,6,6); //左上点
  trRect = QRect(trPoint.x()-2,trPoint.y()-2,6,6); //右上点
  blRect = QRect(blPoint.x()-2,blPoint.y()-2,6,6); //左下点
  brRect = QRect(brPoint.x()-2,brPoint.y()-2,6,6); //右下点
  tcRect = QRect(tcPoint.x()-2,tcPoint.y()-2,6,6); //上中点
  bcRect = QRect(bcPoint.x()-2,bcPoint.y()-2,6,6); //下中点
  lcRect = QRect(lcPoint.x()-2,lcPoint.y()-2,6,6);//左中点
  rcRect = QRect(rcPoint.x()-2,rcPoint.y()-2,6,6); //右中点

  painter.fillRect(tlRect,color);
  painter.fillRect(trRect,color);
  painter.fillRect(blRect,color);
  painter.fillRect(brRect,color);
  painter.fillRect(tcRect,color);
  painter.fillRect(bcRect,color);
  painter.fillRect(lcRect,color);
  painter.fillRect(rcRect,color);
}

void fullScreenWidget::updateMouseShape(const QPoint &point)
{
  switch(currentShotState){
    case initShot:
    case beginShot:
      setCursor(Qt::CrossCursor);
      break;
    case beginMoveShot:
      setCursor(Qt::OpenHandCursor);
      break;
    case finishShot:
    case finishMoveShot:
    case finishControl:
      if(getSelectedRect().contains(point))
        setCursor(Qt::OpenHandCursor);
      else
        updateMoveControlMouseShape(getMoveControlState(point));
      break;
    case beginControl:
      updateMoveControlMouseShape(controlValue); //调用函数对移动8个控制点进行鼠标状态的改变
      break;
    default:
      setCursor(Qt::ArrowCursor);
      break;
  }
}

void fullScreenWidget::updateMoveControlMouseShape(controlPointEnum controlValue){
  switch(controlValue){
    case moveControl1:
    case moveControl5:
      setCursor(Qt::SizeFDiagCursor);
      break;
    case moveControl2:
    case moveControl6:
      setCursor(Qt::SizeVerCursor);
      break;
    case moveControl3:
    case moveControl7:
      setCursor(Qt::SizeBDiagCursor);
      break;
    case moveControl4:
    case moveControl8:
      setCursor(Qt::SizeHorCursor);
      break;
    default:
      setCursor(Qt::ArrowCursor);
      break;
  }
}

fullScreenWidget::controlPointEnum fullScreenWidget::getMoveControlState(const QPoint &point)
{
  fullScreenWidget::controlPointEnum result = moveControl0;
  if(currentShotState == initShot || currentShotState == beginShot)  {
    result = moveControl0;
  }
  else if(tlRect.contains(point)){
    result = moveControl1;
  }
  else if(tcRect.contains(point)){
    result = moveControl2;
  }
  else if(trRect.contains(point)){
    result = moveControl3;
  }
  else if(rcRect.contains(point)){
    result = moveControl4;
  }
  else if(brRect.contains(point)){
    result = moveControl5;
  }
  else if(bcRect.contains(point)){
    result = moveControl6;
  }
  else if(blRect.contains(point)){
    result = moveControl7;
  }
  else if(lcRect.contains(point)){
    result = moveControl8;
  }
  else{
    result = moveControl0;
  }

  return result;
}

QRect fullScreenWidget::getMoveAllSelectedRect(void)
{
  QRect result;
  QPoint tmpBeginPoint,tmpEndPoint;
  int moveX,moveY;
  checkMoveEndPoint(); //对移动选区进行判断，当移动的选区超出边界，则停止移动
  moveX = moveEndPoint.x() - moveBeginPoint.x();
  moveY = moveEndPoint.y() - moveBeginPoint.y();
  tmpBeginPoint.setX(beginPoint.x() + moveX);
  tmpBeginPoint.setY(beginPoint.y() + moveY);
  tmpEndPoint.setX(endPoint.x() + moveX);
  tmpEndPoint.setY(endPoint.y() + moveY);

  result = getRect(tmpBeginPoint, tmpEndPoint);
  return result;
}

QRect fullScreenWidget::getMoveControlSelectedRect(void)
{
  int x,y,w,h;
  QRect rect = getRect(beginPoint,endPoint);
  QRect result;
  switch(controlValue){
    case moveControl1:
      result = getRect(rect.bottomRight(),moveEndPoint);
      return result;
      break;
    case moveControl2:
      x = rect.x();
      y = getMinValue(moveEndPoint.y(),rect.bottomLeft().y());
      w = rect.width();
      h = qAbs(moveEndPoint.y() - rect.bottomRight().y());
      break;
    case moveControl3:
      result = getRect(rect.bottomLeft(),moveEndPoint);
      return result;
      break;
    case moveControl4:
      x = getMinValue(rect.x(),moveEndPoint.x());
      y = rect.y();
      w = qAbs(rect.bottomLeft().x() - moveEndPoint.x());
      h = rect.height();
      break;
    case moveControl5:
      result = getRect(rect.topLeft(),moveEndPoint);
      return result;
      break;
    case moveControl6:
      x = rect.x();
      y = getMinValue(rect.y(),moveEndPoint.y());
      w = rect.width();
      h = qAbs(moveEndPoint.y() - rect.topLeft().y());
      break;
    case moveControl7:
      result = getRect(moveEndPoint,rect.topRight());
      return result;
      break;
    case moveControl8:
      x = getMinValue(moveEndPoint.x(),rect.bottomRight().x());
      y = rect.y();
      w = qAbs(rect.bottomRight().x() - moveEndPoint.x());
      h = rect.height();
      break;
    default:
      result = getRect(beginPoint,endPoint);
      return result;
      break;
  }

  return QRect(x,y,w,h); //获取选区
}

int fullScreenWidget::getMinValue(int num1, int num2)
{
  return num1<num2?num1:num2;
}

void fullScreenWidget::drawSelectedPixmap(void)
{
  painter.drawRect(selectedRect); //画选中的矩形框
  shotPixmap = loadPixmap.copy(selectedRect);  //更新选区的Pixmap
  if(selectedRect.width() > 0 && selectedRect.height()){
    painter.drawPixmap(selectedRect.topLeft(),shotPixmap); //画选中区域的图片
  }
  draw8ControlPoint(selectedRect); //画出选区的8个控制点
}

void fullScreenWidget::drawXYWHInfo(void)
{
  int x,y;
  QColor color = QColor(239,234,228,200);
  QRect rect;
  QString strTipsText;
  switch(currentShotState){
    case beginShot:
    case finishShot:
    case beginMoveShot:
    case finishMoveShot:
    case beginControl:
    case finishControl:
      x = selectedRect.x() + 5;
      y = selectedRect.y() > infoHeight ? selectedRect.y()-infoHeight:selectedRect.y();
      rect = QRect(x,y,infoWidth,infoHeight);
      strTipsText = QString(tr(" 坐标信息\n x:%1 y:%2\n w:%3 h:%4")).arg(selectedRect.x(),4).arg(selectedRect.y(),4)
                      .arg(selectedRect.width(),4).arg(selectedRect.height(),4);
    painter.fillRect(rect,color);
    painter.setPen(QPen(Qt::black));//设置画笔的颜色为黑色
    painter.drawText(rect,Qt::AlignLeft|Qt::AlignVCenter,strTipsText);
    break;
    default:
    break;
  }
}

 screenshot.zip   

    您可以下载下来，进行测试使用。解压文件后，使用qtcreator工具进行加载screenshot.pro文件。执行qmake,build,run。即可。

    注：因我提供的源代码在ubuntu操作系统上编写，如果您使用的是windows操作系统，可能需要qtcreator修改字符集为uft-8即可。本代码使用的是qt4.6.2进行编译，使用emacs编辑器进行编写。